Atomic Spectrometry Update. Industrial analysis: metals, chemicals and advanced materials

Contents

• 1 Metals
  • 1.1 Ferous metals and alloys
  • 1.2 Non-ferrous metals and alloys

• 2 Chemicals
  • 2.1 Petroleum and petroleum products
  • 2.2 Organic chemicals and solvents
  • 2.3. Inorganic chemicals and acids
  • 2.4. Nuclear materials

• 3 Advanced materials
  • 3.1 Polymeric materials and composites
  • 3.2 Semiconductor and conducting materials
  • 3.3 Glasses
  • 3.4 Ceramics and refractories
  • 3.5. Catalysts

• References

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Abstract

This Atomic Spectrometry Update is the latest in an annual series appearing under the title ‘Industrial Analysis’. Due to changes in the abstracting system that the ASU reviews depend upon, there has been a slight change in the quantity and quality of the abstracts that were presented to the writing team this year. For most of the review no significant changes have occurred. However, for several specialised topics such as Glasses and Catalysts the amount of information has both increased in relevance and quantity. In contrast Table 3 is reduced this year due to the abstracting changes. Hopefully, more refinements of the new system will bring in more benefits as to the quality of the review in the coming years.

New developments in solid sample introduction continue to be reported both for ferrous and non-ferrous metal analysis. The technique that has shown much promise in this area is laser induced breakdown spectrometry (LIBS) and several interesting reports were received.

In contrast to the 2000 review, where petroleum additives were a hot topic, only one paper referring to petroleum additives was received. Solid phase micro-extraction (SPME) has also been employed in conjunction with Raman spectroscopy to determine the petroleum contamination of water. The analysis of coal in this review period is split mainly into two areas: the analysis of total trace metals in the coal and the determination of elements which raise environmental concerns.

Papers detailing pre-concentration using various functionalised resins, e.g., XAD-2 and XAD-16, solid phase extraction and various organic chemicals have a large contribution to this year's review. This year there has been a more general application of analytical techniques for analysis of inorganic materials. As in previous years, solid sample analysis has been a prominent feature, with the development of a portable XRF device, several ETA-AAS studies and some interesting secondary ion mass spectrometry work being reported.

Inductively coupled plasma mass spectrometry (ICP-MS), in each of its variants, continues to be the dominant technique in the application of analytical atomic spectroscopy to the analysis of nuclear materials.

One point for avid review readers is the quantity of rare earth element papers mentioned in Table 3 this year. This may be due to either the new abstracting system or to the fact that our colleagues who publish in this area around the world are growing weary of this field of research.

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1 Metals

The analysis of ferrous, non-ferrous metals, and their alloys by analytical atomic spectrometry is covered in this section. A summary of the analytical methods reported for metals in the time period under review is given in Table 1.

Table 1 Summary of analyses of metals

Element	Matrix	Technique; atomization; analyte form^a	Sample treatment/comments	Ref.
a HG indicates hydride and S, L, G and Sl signify solid, liquid, gaseous or slurry sample introduction, respectively.
As	Brass	AF;HG;L	Sample (0.1 g) was dissolved in HNO3 (1∶1) and H2SO4 (1∶3) under heat. Upon cooling the residue was dissolved in HCl (1∶1) and treated with 10 ml of 100 g l^−1 KI and 15 ml of 100 g l^−1 ascorbic acid. After standing for 30 min, 5 ml of 50 g l^−1 thiourea and 5 ml of HCl (1∶1) were added. An aliquot (15 ml) was injected into the hydride generator with 20 g l^−1 KBH4 and 5 g l^−1 KOH. Detection limit: 0.2 ng ml^−1	27
Au	Gold alloys	AE;laser;S	None	18
Au	Gold alloys	AE;GD;S	None	20
Bi	Steel	AA;FI-ETA;L	Bi was complexed with the ammonium salt of dithiophosphoric acid OO-diethyl ester and pre-concentrated on activated carbon. Ethanol was used as an eluent	14
Cu	Aluminium alloy	AE;ICP;L	Samples were dissolved in HCl with high pressure digestion or wet acid dissolution with H2SO4	28
H	Steel	SIMS;-;S	None; qualitative analysis and distribution	4
Mo	Steel	AA;F;L	Samples (0.1 g) were dissolved in 5 ml aqua regia, 10 ml water, and 2 ml HNO3. Appropriate amounts of triethanolamine and dodecyltrimethylammonium were added so that the final concentrations were 60 and 16 g l^−1 in 100 ml with dilution with water. Interference from steel matrix components was eliminated	29
Pb	Steel	AA;FI-F;L	Samples (0.1–1 g) were dissolved in 3 ml HNO3 and 3 ml HCl, then evaporated to dryness. The residue was dissolved in 30 ml of 1 M HNO3 and passed through a flow injection column with Pb-Spec selective resin. Pb was eluted with 0.1 M ammonium oxalate through the flow injection manifold and into the FAAS. Detection limit: 0.5 µg	15
Pb	Steel	AA;FI-ETA;L	Pb was complexed with the ammonium salt of dithiophosphoric acid OO-diethyl ester and pre-concentrated on activated carbon. Ethanol was used as an eluant	14
Pd	Lead based alloy	AA;F;L	The alloy (0.5 g) was dissolved in 10 ml HNO3 (30%) and the undissolved tin and tin oxides were removed by filtration. Lead was precipitated by the addition of ammonium sulfate. The remaining filtrate was diluted to 100 ml with water. An aliquot (10 ml) was adjusted to pH 2 in 100 ml and passed through an Amberlite XAD-16 column (30 mm × 10 mm id, 0.2 g). The retained Pd was eluted by both 5 ml of 1 M KCN and 5 ml of 10% HCl. The eluates were combined and 0.5 ml of 5% Cu solution was added, then the solution analysed. Detection limit: 0.05 mg l^−1	30
Sb	Brass	AF;HG;L	Sample (0.1 g) was dissolved in HNO3 (1∶1) and H2SO4 (1∶3) under heat. Upon cooling the residue was dissolved in HCl (1∶1) and treated with 10 ml of 100 g l^−1 KI and 15 ml of 100 g l^−1 ascorbic acid. After standing for 30 min, 5 ml of 50 g l^−1 thiourea and 5 ml of HCl (1∶1) were added. An aliquot (15 ml) was injected into the hydride generator with 20 g l^−1 KBH4 and 5 g l^−1 KOH. Detection limit: 0.3 ng ml^−1	27
Se	Copper	AE;FI-HG-ICP;L	The dissolved sample was passed through a Dowex 1-X8 anion exchange microcolumn to separate Se from the matrix. Se^VI was reduced in a heated PTFE reaction coil, then the hydride was formed from an aliquot of HCl and sodium tetrahydroborate in solution. Detection limit: 0.4 µg l^−1	31
Se	Steelmaking wastes	MS;ICP;L	Different Se species were extracted in two steps: 1, Cr^VI and soluble Cr^III were leached by a solution of NaOH–Na2CO3; 2, insoluble Cr^III and Cr metal were fused with NaHSO4 and extracted with KCl. The solutions passed through anion exchange columns Dowex 1-X8 and Dowex 50W-X8, for Cr^VI and Cr^III, respectively. Determination by ICP-MS followed elution by HNO3 (Cr^VI) and HCl (Cr^III). Detection limits: 0.1 µg g^−1 for both Se species	10
Si	Aluminium alloy	AE;ICP;L	Samples were dissolved in HCl with high pressure digestion or wet acid dissolution in H2SO4. Si was lost during wet acid dissolution if HCl was used	28
Si	Aluminium alloys	XRF;-;S	Samples were chill cast prior to abrasive surface finishing	23
Te	Nickel based alloy	MS;FI-HG-ICP;L	The dissolved sample was mixed with a masking agent solution of 0.1% m/v L-cysteine and 0.5% m/v thiourea. Detection limit: 27 ng g^−1	11
Ti	Titanium coated steel and tungsten carbide	TOFMS;ICP;S	None; depth profiling	5
Zn	Aluminium alloys	AA;F;L	Zinc was adsorbed on [1-(2-pyridylazo)-2-naphthol] complex on microcrystalline naphthalene from the dissolved sample. The complex was filtered and dissolved in 5 ml of dimethylformamide prior to analysis	32
Various	Aluminium alloyed steel	SIMS;-;S	None; elemental characterization	33
Various (11)	Aluminium and gold-palladium alloy	XRF;-;L	The analytes were extracted from the dissolved sample with diethyldithiocarbamate. A pre-concentration factor of 500 was obtained	34
Various (5)	Copper, high purity	AE;FI-ICP;L	L-Cysteine was used to reduce interfences from the copper matrix. Analyte separation from the matrix is not necessary. Detection limits: 0.1, 0.3, 0.05, 0.3, and 0.6 µg g^−1 for As, Bi, Ge, Sb, and Sn, respectively	35
Various	Copper coins	XRF and PIXE;-;S	None	21
Various	Dental alloys	AE;GD;S XRF;-;S	None	22
Various (3)	Ferroalloys	MS;spark ablation ICP;S	Powdered metal samples mixed with graphite (1∶2 ratio) and pressed into pellets	7
Various	Iron	MS;LA-ICP;S	None	6
Various (7)	Iron	MS;ICP;L	Samples (1 g) were dissolved in HNO3 and HCl. Analytes were separated by solid phase extraction using bonded silica with octadecyl (C18) after the addition of tartaric acid as the masking agent and sodium diethyldithiocarbamate as the chelate. Elution was with HNO3 and H2O2	36
Various (20)	Iron	MS;ICP;L	The dissolved sample was passed through a mixture of anion and cation exchange resins packed in a single mini-column. The iron was removed with a 1 M HF solution, then the analytes were eluted by a solution of HNO3 and H2O2	37
Various (5)	Low-alloy steel	AE;HG-ICP;L	Samples (0.1 g) were dissolved in 10 ml aqua regia without heat. L-Cysteine (0.5 g) was dissolved in water, then added to sample, and water added to 800 ml. The pH was adjusted to 1.56 then brought to 1000 ml. Sodium borohydride (1.5% m/v) was used to form hydrides. Detection limits: 0.2 µg l^−1 for As, Bi, Sb, Sn and 0.1 µg l^−1 for Ge	13
Various (7)	Low alloyed steel	AE;laser;S	None	2
Various (17)	Mercury	AA;F;L	A sample (5 g) was dissolved in 4 ml HNO3. Formic acid was added until the mercury was completely reduced and filtered. The remaining filtrate was evaporated to a moist residue then taken up in 2 ml 10% HNO3 and brought to 10 ml with water. Detection limits: 1–10 ng g^−1	38
Various	Nickel alloy	PIXE;-;S	None	39
Various	Nickel based alloys	XRF;-;S	Powdered alloy samples were prepared in a dilithium tetraborate flux with addition of lithium carbonate, potassium sodium carbonate, and sodium nitrate as an oxidizing agent	24
Various (16)	Nickel alloys	XRF;-;S	Molten samples poured into 30–50 mm diameter moulds and then polished	40
Various (18)	Osmium powder	AE;ICP;L	Sample was dissolved in HNO3 then osmium was reduced and treated with NaOH for matrix removal. The residual solution was analysed. Detection limits: 0.005–0.13 µg ml^−1.	41
Various (3)	Molybdenum–silicon–boron alloy	AE;ICP;L	Samples were dissolved in 10 ml of H2SO4, 1 ml of HNO3, 2 ml of HF and 12 ml of water for major component analysis. Complete dissolution at room temperature was reported	42
Various	Gold–silver–copper alloys	AE;laser;S	None	17
Various (14)	Silver coins	XRF;-;S	None	43
Various (12)	Silver coins	XRF;-;S	None	44
Various	Silver and palladium brazing filler metals	MS;GD;S	Minimal preparation required. Precision: major elements 1% RSD and trace elements 20% RSD	45
Various (5)	Tool steel	AE;FI-ICP;L	Samples were dissolved by on-line electrolytic dissolution with 1.5 M HNO3 as a dissolving and conducting medium	12
Various	Zirconium based alloys	MS;GD;S	Disk samples were dry polished with 120 grit zirconium oxide endless paper	46

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1.1 Ferous metals and alloys

New developments in solid sample introduction continue to be reported. A high resolution echelle spectrometer was used with laser induced breakdown spectrometry (LIBS) for alloy identification.¹ Automated identification methods, such as principal component analysis and cluster analysis, demonstrated that metals could be classified into groups based on their LIBS spectra with 97% accuracy. Spectral matching of 234 individual spectra of a library of 39 average spectra gave 97.4% correct prediction of material class and 79.9% correct identification of the specific alloy. Metal samples included various steels, zirconium alloys, nickel alloys, brass, copper and aluminium. LIBS was also applied to the analysis of low alloyed steel.² The analytical sensitivity for C, S, P, Mn, Si and Cr was reported to be enhanced under the conditions described and the limit of detection to be <10 µg g⁻¹.

The determination of oxygen in steel by atomic emission spectrometry was demonstrated. The oxygen concentrations found, during the ladle refining process, correlated well with oxygen determined in rolled billet samples.³ A review was written that covered the application of secondary ionization mass spectrometry (SIMS) to the determining of the distribution of hydrogen trapping sites in steels.⁴

Laser ablation ICP-MS with time of flight mass spectrometry (LA-ICP-TOFMS) was applied to the depth profile analysis of Ti coatings on steel and tungsten carbide.⁵ A laser repetition rate of 3 Hz, 120 µm crater diameter, and 100 mJ laser output gave linear calibration that was independent of the dwell time or peak area used for calibrating the thickness of the layer. The depth resolution was reported to be 0.20 µm per laser shot.

Spatially resolved trace analysis of early medieval archaeological iron finds was accomplished by LA-ICP-MS.⁶ Conditions were set so that 100 µm diameter ablation craters were sampled. The method was validated by the analysis of steel and iron reference materials and by comparisons with electron microprobe analysis. Precision was found to be limited by the material rather than by the instrument conditions. Spark ablation ICP-MS was used for semi-quantitative determination of impurities in three types of alloys: Fe–Ti, Fe–Nb and Fe–V.⁷ Samples of alloy powder were mixed 1∶2 with graphite and pressed into pellets. This was done to reduce the amount of metal that would be ablated. More material is ablated by a spark erosion device than by a laser ablation system and this could potentially block the interface region of the ICP-MS.

Relative sensitivity factors for carbon and nitrogen in steels by glow discharge mass spectrometry (GDMS) were optimised.⁸ The ion beam ratios increased with increasing discharge voltage, with decreasing discharge current, and with increased mask size (at constant discharge conditions). Pulsed glow discharge atomic emission spectrometry was evaluated for depth profiling.⁹ It was found that an inverse relationship exists between depth resolution and both the discharge pulse width and pulse frequency. This was applied to the measurement of a thin copper coating (50 nm) on steel.

Solution analysis applications continue to be used for metal analysis. Many are noted in Table 1, however some applications are worth a mention. Chromium speciation, in steels and solid waste from steel making, was accomplished by selective retention on ion-exchange media followed by elution and determination by isotope dilution ICP-MS.¹⁰ Although sample preparation was quite involved, detection limits of 0.1 µg g⁻¹ were reported. Cr^VI and Cr^III were retained on Dowex 1-X8 and Dowex 50-X8 ion exchange resin, respectively. Elution was effected by HNO₃ (for Cr^VI) and by HCl (for Cr^III).

Flow-injection hydride generation ICP-MS was used to determine tellurium in nickel-based superalloys.¹¹L-Cysteine (0.1% m/v) and thiourea (0.5% m/m) were found to be effective masking agents. The determination was done by both the method of standard addition and isotope dilution. The method limit of detection was estimated to be 27 ng g⁻¹.

An on-line electrolytic dissolution system was used for the determination of Fe, W, Mo, V, and Cr in tool steel by a flow injection ICP-AES system.¹² A 1.5 M HNO₃ solution dissolved the sample and closed the electric contacts between the electrodes. A sample throughput of 30 solid samples per hour (150 determinations) was reported. A matrix independent method for determining hydride-forming elements in steels by hydride generation ICP-AES was reported.¹³ Dilute sample solutions (0.1 g in 1000 ml) were prepared with L-cysteine (0.5 g l⁻¹) at a pH of 1.56 and calibration standards were prepared from aqueous standards with the same concentration of L-cysteine.

Two flow-injection systems for flame atomic absorption spectrometry were reported. An automated system was used to determine Bi and Pb in steels with pre-concentration on activated carbon after complexation with the ammonium salt of dithiophosphoric acid OO-diethyl ester.¹⁴ In the other paper, Pb was retained on a lead selective resin and eluted with an ammonium oxalate solution.¹⁵

1.2 Non-ferrous metals and alloys

As was noted in the previous section, solid sample analysis continues to be a major focus in the literature. LIBS was applied to the in situ analysis of molten zinc and aluminum alloys.¹⁶ Satisfactory results were reported after method optimization and implementation with customized software. LIBS was reported to be successfully used for the determination of gold and silver in Ag–Au–Cu alloys with a partial least square regression algorithm.¹⁷ This was proposed as a simple, rapid, and low cost method for the analysis of jewellery pieces. Another LIBS method was reported to be effective in determining precious metal alloy components down to the trace level (1 µg g⁻¹) without calibration.¹⁸ The accuracy of the method was not affected by the matrix nor the object shape. Nano- and femtosecond laser pulses were compared in LIBS analysis of brass samples.¹⁹ Linear calibration curves were obtained with the internal standardization of Zn to Cu.

Gold was determined in alloys by glow discharge atomic emission spectrometry.²⁰ Whenever possible copper and silver were used as an internal standard. Precision was greater than 1 part per thousand, which is poorer than the precision from standard methods.

Proton-induced X-ray emission (PIXE) and X-ray fluorescence (XRF) spectrometry were compared through the analysis of old Japanese copper coins.²¹ PIXE required selective filtering for analysis whereas XRF was more practical for the analysis. The relative levels of low concentration elements were found to identify the origin of the coins.

The analysis of dental alloys was investigated by energy dispersive XRF (EDXRF) and glow discharge atomic emission spectrometry (GD-AES). Determinations by EDXRF were reported to be in agreement with those from GD-AES.²² A chill casting method for aluminium alloys prior to abrasive surface finishing was proposed for XRF determination of silicon in the alloys.²³ This was reported to remove the positive bias due to “smearing” of silicon during abrasion without chill casting and was confirmed by atomic emission spectrometry. A fusion method for refractory nickel based alloy powders for XRF analysis was proposed.²⁴ A dilithium tetraborate flux with addition of lithium carbonate, potassium sodium carbonate and sodium nitrate as an oxidizing agent was effective in making stable glass fusion discs for samples and synthetic standards.

The local structure of phosphorus atoms in a nickel–phosphorous alloy was studied by X-ray absorption fine structure (XAFS) spectrometry and X-ray diffraction spectrometry.²⁵ Although, this is not a quantitative technique, it is useful in determining near neighbour elements and potential intermetallic bonds that can occur within an alloy.

A review of gold analysis was written that covered classical and spectrometric methods for both geological and metallurgical samples.²⁶ The review emphasized verification of results through quality control data.

2 Chemicals

2.1 Petroleum and petroleum products

2.1.1 Petroleum products. In contrast to the 2000 review, where petroleum additives were a hot topic, only one paper⁴⁷ referring to petroleum additives was received. This paper describes the determination of methylcyclopentadienylmanganese tricarbonyl (MMT) (as Mn) by solid-phase microextraction (SPME)-direct thermal desorption-quartz furnace AAS. Working MMT solutions were prepared in 40 ml amber vials and sampling was performed by exposing the SPME fibre to the headspace over vigorously stirred samples for 15 min. The analytical performance of the system was as follows: detection limit for MMT was 0.71 ng ml⁻¹ (as Mn) with a RSD of 4%.

Solid-phase microextraction (SPME) was also employed in conjunction with Raman spectroscopy to determine the petroleum contamination of water. The solid phase consisted of a small volume of poly(dimethylsiloxane) that had an optical window of 830–1600 cm⁻¹ in the Raman shift region. This region is suitable for determining both aromatic and aliphatic fuel components. Several sample types were analysed e.g., Jet A1, aviation gasoline, unleaded gasoline, and these were detected without any problem. The results attained for this approach compared favourably with the standard methods of purge and trap gas chromatography and liquid–liquid extraction followed by IR.⁴⁸

The sulfur content in petroleum products is on an ever-downward trend: it is therefore important that refineries have the capability to determine sulfur at the lower levels. There are a few techniques that are capable of determining sulfur at the required low (ppm) levels; here a GC-AED method is reported for low level determination of sulfur and nitrogen.⁴⁹ The optimisation of parameters such as element wavelength, detector gas flow rates and chromatographic conditions has improved the selectivity of nitrogen and sulfur in the presence of hydrocarbons; the detection improvement is a 10-fold increase for sulfur and >100-fold for nitrogen.

Organic and inorganic arsenic compounds in thermally cracked gasoline are known to be catalyst poisons in the aromatisation process. Nakamoto et al. have developed a simple and rapid method for such determinations.⁵⁰ By the addition of nickel nitrate as a matrix modifier a simple and rapid method was established. A detection limit of 10 ng g⁻¹ was achieved with a RSD of 3.1%; the variation in gasoline type and presence of other metals did not affect the results attained. Similarly the determination of mercury in light hydrocarbon fractions and natural gas condensates is an important issue in the petroleum industry because of catalytic poisoning. Ceccarelli and Picon developed two fast reliable methods namely atomic fluorescence spectroscopy with thermal desorption (AFS-TD) and atomic absorption spectroscopy with electrothermal atomisation (AAS-ETA). Statistical analysis showed both techniques were statistically equivalent.⁵¹ Equally it is at times useful to be able to analyse for mercury in the field, a new technique based on traditional concepts has been developed for rapid on-site analysis of mercury in environmental media. In the method mercury is analysed by integration of thermal decomposition, amalgamation and atomic absorption spectrometry (TDA-AAS). Sample preparation and analysis are essentially integrated into a single instrumental system. The system has been fully validated and had been used in a series of field studies in conjunction with remediation of mercury-contaminated soil at natural gas utility sites (solids can be analysed directly without chemical pre-treatments). Reasonable agreement has been demonstrated between TDA-AAS on-site results and laboratory results using traditional mercury analysis. As a result the TDA-AAS demonstrates lab-quality results on site; this has been developed as a method for the United States Environmental Protection Agency (US EPA), Method 7473.⁵² A method for the determination of total mercury in natural gas liquid and condensate is described,⁵³ the trace amount of mercury being concentrated by adsorption onto activated carbon powder. The activated carbon was isolated and subsequently analysed using slurry sampling ETV-AAS. Triton X-100 at 5000 µg ml⁻¹ was necessary to disperse the adsorbed carbon powder into a homogenous slurry. Palladium was used as a chemical modifier, to stabilize the mercury and enhance sensitivity. A detection limit of 2 ng ml⁻¹ with a RSD of 8.4% resulted.

2.1.2 Fuels. The analysis of coal in this review period is split mainly into two areas: the analysis of total trace metals in the coal and the determination of elements which raise environmental concerns.

Various techniques have been employed to determine the trace elemental composition of coal, which include ICP-MS, FAAS and radioisotope X-ray fluorescence. Richaud et al.⁵⁴ report on the analysis of coal gasification plant samples (chars and fines) by ICP-MS and subsequent validation via the comparison of results from two laboratories. Several sample digestion methods have been compared: peroxide fusion (sodium peroxide and sodium carbonate) and microwave digestion (laboratory 1); wet ashing (open acid) and microwave digestion (laboratory 2). The samples were obtained from a pilot-plant scale coal gasification rig. The digestions were carried out using a range of sample masses, as small as 10 mg. In general the elemental concentrations (1–150 mg kg⁻¹) were in good agreement. However, all digestion techniques appeared to lose mercury and alternative methodology was used. Limitations of the various digestion routes and methodology are discussed in detail.

ICP-MS has also been used as a reference technique for the comparison of two semi-quantitative atomic emission spectroscopic methods and a quantitative method in which the coal ash was vaporized in an arc of constant current and pure coal power with Pd as an internal standard. Comparable results were obtained for Ga, Ge, Sn, Ni and Co by the three methods but the Ba, Sr, Si, Y, Yb and La were lower when determined in the ash than in coal. The ICP-MS was then used for the determination of REE in HCl extracts from coal and gave results in good agreement with determinations by the other methods directly on coal. The ICP-MS results indicated that the REE in the coals occur in easily dissolved compounds and that the method is reliable for semi-quantitative determination of REE directly in coals.⁵⁵ As a matter of interest the REE contents in some coals exceeded those in REE ore deposits and thus coal beds may be economically feasible sources of REE. This was also noted in last year's review, in relation to Ge in coal ash.

A new instrument variation on laser induced breakdown spectroscopy (LIBS) that allows simultaneous determination of all detectable elements is reported. It uses a multiple spectrograph and a synchronous multiple charge coupled device spectral acquisition system. The system is particularly suited to the analysis of heterogeneous materials such as coal and mineral ores. Key inorganic components of coal, namely Al, Si, etc., in addition to C and H are detected. Detection limits are typically 0.01% for as received moist materials, measurement repeatability and accuracy being within ±10% absolute, which is similar to standard analysis procedures for heterogeneous materials. Beta versions are currently being used routinely in two commercial coal fired power stations. Perhaps we will hear more information on its performance in the field in the next review period.⁵⁶

An EDXRF system has been evaluated for the major, minor and trace elements in coal, using a radioisotope source in preference to an X-ray tube. It is concluded that the performance of the instrument can be considered adequate for a quick indicative analysis. The lifetime of neither the source nor the disposal route is indicated.⁵⁷

Coal with low ash content is important in the coal and steel industry for obvious reasons. The conventional method used is to burn the coal, remove the carbon and determine the remaining ash via weighing. A new method has been developed at the Nuclear Research Centre of Iran, working on the basis of the absorption of the dual energy gamma-ray by coal. The paper presents comparative data from conventional methods and the new method. They also report that for SiO₂, Al₂O₃, TiO₂, Na₂O and K₂O there is a linear relationship between these oxides and the ash content but not for Fe₂O₃, CaO, SO₃ and MgO, so one cannot predict ash by determining the metal oxides.⁵⁸

In the USA alone, 52 tons of mercury per year are released into the atmosphere from coal-fired power stations. In an attempt to control the release, coal fired power stations (over 420 MW) have to monitor their mercury levels in coal on a regular basis. A fully automated system, based on continuous flow vapour generation AFS, is described⁵⁹ detailing digestion procedures and results for coal and coal ash certified materials.

In the last review period there was a noted push to analyse coal directly, with minimum sample preparation: this is not so evident within this review period. One paper reports the use of slurry ETV-ICP-MS for the analysis of As, Pb, Mn and Se in coal.⁶⁰ The slurry is prepared by mixing the powdered coal (<45 µm) with aqueous 5% v/v nitric acid solution in an ultrasonic bath. An ultrasonic probe is used to homogenize the slurry in the auto-sampler just before its introduction into the graphite tube. By introducing 10 µl of the 4.0 mg l⁻¹ coal slurry, using 3 µg of Pd as matrix modifier and a pyrolysis temperature of 600 °C, samples of reference coals were analysed and were in good agreement with reference values. No carrier had to be added in addition to the Pd modifier.

Microwave digestion techniques have been explored and contrasted in the digestion of residual fuel oil samples. In one paper⁶¹ an open and two closed microwave systems are compared. The three systems were evaluated in terms of accuracy and precision, reagents and time saving, total organic carbon content and limits of detection, i.e., a thorough evaluation. The total organic carbon content in both closed systems was much higher than the open vessel system, but one can hardly say that this was very surprising. Various elements had problems in the different systems, e.g., Co was lower (<80% recovery) when using the closed system and the open vessel system often had low recovery on many elements. For the majority of elements the RSDs were <5% in the closed system and >10% for the open system: comparison of the data with that attained via traditional methods may have been useful.

A detailed study of microwave conditions required to carry out a digestion procedure on residual fuel oil has been reported.⁶² The influence of sample size, reagent composition and volume, microwave power and duration of heating on the digestion procedure were all studied. A nine step heating programme, 36 min, with microwave power not exceeding 450 W in the pulse mode was found most suitable for the digestion of 250 mg of fuel oil with a mixture of nitric acid (5 ml) and hydrogen peroxide (2 ml). Various other parameters were varied when problems occurred with the recovery of some elements. The reviewer’s main concern about this work is that the whole process was fine tuned using only one sample (NIST SRM 1634b): it would have been useful to compare the results with previously analysed samples. A third paper⁶³ compares and contrasts closed vessel microwave with wet oxidation at 150 °C with overnight ashing at 520 °C of heavy fuel oil. The microwave procedure took 30 min, comparative data was good and detection limits of 0.1 µg g⁻¹ were achieved using ICP-MS

The determination of sulfur by solution nebulization ICP-MS is difficult because of the interference of the oxygen dimer ¹⁶O₂ on the most abundant isotope of sulfur, ³²S. This is particularly difficult if water is the solvent. High accuracy isotope dilution mass spectrometric (IDMS) determination of sulfur requires the ratio of ³²S∶³⁴S to be measured. In this reported work⁶⁴ electrothermal vaporization was used to generate a water free aerosol of the sample. Further reduction of the oxygen dimer was achieved using nitrogen as an oxygen scavenger in the argon plasma. Once all the necessary changes had been introduced the system worked very well and a detection limit of 4 ng g⁻¹ was achieved. Two fossil fuel reference materials were in good agreement with those obtained by thermal ionisation mass spectrometry (TIMS).

2.1.3 Oils. This review period has seen a concentration of determining one or two elements in oil products rather than the normal suite of additive and trace metals. This is borne out by 3 papers detailed below where ETV-AAS is used as the technique of choice and we see a decrease in this review period in the use of ICP-AES.

The quantitative determination of wear metals in used lubricating oil has been an application of great interest for several years. The analysis has been used as an indicator of wear in metallic components of engines and turbines. Usually this analysis monitors elements such as Cr, Cu, Fe, Ni, Zn, etc. Querioz Auccelio et al.⁶⁵ suggest the determination of Sn and Sb are indicative of specific bearing wear and have developed an ETV-AAS method for the sequential determination of Sn and Sb in used lubricating oil. The graphite tube is treated with ruthenium as a permanent matrix modifier, which aids the pyrolysis of the oil matrix at high temperature without significant loss of the elements of interest. The lubricating oil was introduced into the furnace as an oil-in-water microemulsion: this made calibration by direct comparison with aqueous standards possible. The determination was performed sequentially using a multi-element routine. Good spike recoveries were recorded and sub µg l⁻¹ limits of detection were estimated for both elements.

Similarly a comparative study of ETVAAS methods for the determination of silver in used lubricating oils was carried out.⁶⁶ Three methods were developed and evaluated. The first method involved direct sampling into the furnace (using either platform or filter furnace technique) after dilution with an organic solvent mixture. In the second method, silver was determined after microwave digestion. The final method involved introducing the samples as an oil-in-water micro-emulsion. The three methods had similar detection limits, the advantage of the emulsification procedure being the higher sample throughput and the use of aqueous standards.

An increase in automation is the next step taken in this series of papers. On-line emulsification of lubricating oils in a flow injection system for chromium determination by EVAAS is the subject. A 1 ml plug of sample solution was injected into the carrier stream, hexane, and was subsequently mixed with streams of 3.8% (m/v) NaCl, 5% (v/v) Na dodecylsulfate and 5% (v/v) of sec-butanol. The sonification of the flowing solution improved the stability of the emulsion and provided quantitative recoveries. The method is linear for Cr from 7–50 µg l⁻¹ with a detection limit of 4 µg l⁻¹. Good agreement between the certified and found results for two NIST certified materials was attained.⁶⁷

The determination of mercury raises its head in most products associated with the oil industry, in this case crude oil. Liang et al. have built a simple system based on thermal decomposition for a one-step determination.⁶⁸ Samples of crude oil and related products were directly introduced into the system without the use of chemicals and digestion procedures. After 4 min, matrices and mercury compounds were decomposed, elemental mercury was collected on a gold sand trap and detected by AFS. In principle, any sample can be analysed by this method providing the sample can be introduced into the system quantitatively. The detection limit was approximately 0.2 ng g⁻¹ for crude oil, and the results were independent of mercury species and sample types.

The behaviour of a single-bore high-pressure pneumatic nebulizer system (SBHPPN) was put through its paces with the analysis of lubricating oil by FAAS. The effects of sample oil content (from 70–100% (w/w) oil in 4-methylpentan-2-one (IBMK)), the carrier nature (IBMK and methanol) on the characteristics of the aerosols generated, on the analyte transport efficiency and on the analytical results, were investigated. A pneumatic concentric nebulizer (PCN) was used for comparison. High oil content with the PCN gives rise to coarser aerosols, making it impossible to nebulize samples with an oil content of >70% (w/w). With the SBHPPN the viscosity of the sample hardly affects the characteristics of the primary aerosol, and in return it provides higher sensitivities and lower detection limits.

Two papers concern themselves with the characteristics of crude oil, one a spectral characterisation and the other identification of different crude oil sources by carbon isotopic composition. Time resolved laser induced fluorescence (TRF) was used to attain spectral characteristics of 4 different crude oils. TRF spectra were excited by pulsed laser radiation at 250 nm, being measured along the trailing edge of the pulse laser at regulated time intervals. Contour diagrams of equal fluorescence intensities were then constructed to serve as a unique fingerprint of the crude oils.⁶⁹ Biodegraded oils are widely distributed in the Liaohe Basin, China. In order to develop effective oil source correlation tools specifically for the biodegraded oils, carbon isotopic compositions of individual n-alkanes from crude oils and their ashphaltene pyrolysates have been determined by gas chromatography isotope mass spectrometry. The author concludes comparison of the n-alkane isotopic compositions of the crude oils with those of their ashphaltene pyrolysates is a viable method for the differentiation of organic facies variation and post generation alterations.⁷⁰ Both these techniques could be used for remote characterization of crude oils.

2.2 Organic chemicals and solvents

2.2.1 Chemicals. Papers detailing pre-concentration using various functionalised resins, e.g., XAD-2, XAD-16, solid phase extraction and various organic chemicals have made a large contribution to this year's review. The dominance of ETV-AAS has not continued into this review period, possibly because the pre-concentration steps enable the use of other techniques, e.g. FAAS, to attain better detection limits without having to use ETVAAS.

The use of resins in pre-concentration invariably means the resin is functionalised prior to use. Thiosalicylic acid (TSA) modified Amberlite XAD-2 (AXAD-2) was synthesized by coupling TSA with the support matrix AXAD-2 through an azo spacer. This newly designed resin quantitatively absorbs Cd^II, Co^II, Cu^II, Fe^II, Ni^II and Zn^II at pH 3.5–7.0. HCl or HNO₃ (2 M) instantaneously elutes all the metal ions. The pre-concentration factor was between 180–400, the detection limits using FAAS achieved were 0.2–4 µg l⁻¹. The system was used to analyse river and tap water and multivitamin tablets.⁷¹

An on-line cadmium pre-concentration method uses, for the retention of Cd, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) Amberlite XAD-16 at pH 9.5. The cadmium was removed from the micro-column in counter-current with HNO₃. An enrichment factor of 60 was obtained with respect to ICP-AES, with a detection limit of 0.04 µg l⁻¹ being attained.⁷² XAD-16 resin was also employed to pre-concentrate silver from thiocyanate solution. Here the XAD-16 was not functionalised. A concentration factor of 75 was realized.⁷³

Solid phase extraction (SPE) has been used in various studies reported in this review period as a means of performing pre-concentration. In its simplest guise, trace metals were pre-concentrated in high purity iron by SPE coupled to ICP-MS. The solid phase was bonded silica with octadecyl (C₁₈) as the sorbent. The sample (1 g) was dissolved in nitric acid–hydrochloric acid, subsequently adding tartaric acid as the masking agent. The analytes were separated by sodium diethyldithiocarbamate (DDTC) as a chelate from the matrix by SPE after adjustment of the pH and addition of DDTC. Excellent detection limits were achieved for various elements.³⁶

Microcrystalline naphthalene as the solid phase was used to pre-concentrate bismuth and copper in large volumes of water prior to analysis by differential-pulse polarography. The microcrystalline naphthalene alone absorbs bismuth and copper as 1-(2-thiazolyazo)-2-naphthol complexes in the pH range 7.2–9.0 and 4.0–7.8, respectively. The detection limits reported are 55 ng l⁻¹ for Bi and 91 ng l⁻¹ for Cu.⁷⁴ Microcrystalline naphthalene as the solid phase was also used to separate trace indium in geological samples, a detection limit of 12 ng g⁻¹ being attained using ICP-AES.⁷⁵ SPE has also been exploited as an aid to understanding of the isomers generated in biodesulfurization against methylated dibenzothiophenes, i.e., asymmetrically methylated dibenzothiophenes (mDBTs), e.g., 1-, 2-, 3- and 4-methyldibenzothiophenes present in fossil fuel. It is reported that these mDBTs are efficiently degraded by the bacterial strain Rhodococcus erythopolis KA2-5-1. Separation and concentration of the microbial desufurization products from each of the mDBTs could be carried out with high efficiency and reproducibility by the SPE procedure. Identification of the products was via the use of GC, GC-AED, GC-MS and ¹H NMR. The analytical data obtained suggested that the desufurization reactions against mDBTs by this bacterial strain might occur through specific carbon–sulfur bond-targeted cleavages that can be affected by the positions of the methyl groups.

The use of 18-crown-6 is reported in two papers.⁷⁶ The first reports of a new method for the separation of La^III and Ba^III as their thenoyltrifluoroacetone (TTA) complexes with dibenzo-18-crown-6 (DB18C6) in o-dichlorobenzene. This is achieved by means of synergistic extraction and back extraction combined with ICP-AES.

Chemicals with complexing characteristics are also heavily used in the field of pre-concentration; dimethylglyoxime was used for the determination of nickel after on-line sorbent pre-concentration by FI-FAAS.⁷⁷ Similarly, 1-nitroso-2-naphthol was used as the complexing agent for the determination of copper after FI on-line sorbent pre-concentration by FI-AAS:⁷⁸ these procedures are reported by the same author. The absorbent properties of 1,5-diphenylcarbazone–naphthalene with palladium enabled the development of a selective, sensitive, rapid and simple AAS method for the determination of palladium in water.⁷⁹ Zendelovska et al.⁸⁰ have carried out a detailed study on the applicability of tetramethylenedithiocarbamate (TMDTC⁻) and hexamethylenedithiocarbamate (HMDTC⁻) for colloid flotation separation of manganese in traces from fresh (spring, well and tap) water. They found that a higher enrichment of manganese was achieved when a larger amount of HMDTC⁻ was used. Applying iron(III) hexamethylenedithiocarbamate, Fe(HMDTC⁻) as a precipitate collector, manganese was determined at µg l⁻¹ levels.

Chinese Medicines (TCMs) and associated materials did not have such a high profile as last year; there was, however, still a fair representation. Three papers^81–83 detailed the determination of trace elements in TCMs and heroin and sample preparation routes included the use of microwave digestion and open vessel digestion. As with many other sample sectors there is a need to not only study the benefits of some of the trace metals but also to ensure that the toxicity of certain metals is understood. Wu et al.⁸⁴ investigated the amount of heavy metals (As, Hg, Pb) leachable from several Chinese mineral medicines (Realgar, Cinnabaris, Calomelasin, etc.) under conditions simulating those in the stomach upon digestion. Hg and Pb were determined by ICP-MS and a hyphenated technique combining hydride generation with atomic fluorescence spectrometry was used for trace As. Cold vapour (CV)-AAS was used to determine mercury in Chinese medicines after closed vessel microwave digestion in a different study.⁸⁵

Tetramethylammonium hydroxide solution is often used as a chemical modifier to suppress the loss of the volatile elements during electrothermal vaporization. A procedure for the determination of fluoride ion in aqueous solutions has been developed. The use of a tungsten boat furnace (TBF) vaporization system coupled to ICP-AES has been validated. A micro-volume of aqueous sample solution and the addition of tetramethylammonium hydroxide as a chemical modifier to suppress the loss of fluoride enabled the successful determination of fluoride in aqueous solutions. This procedure was successfully used to analyze several leachings from rubber samples made of fluorocarbon polymer.⁸⁶ Tetramethylammonium hydroxide (TMAH) was also used in the determination of volatile elements (Ag, Cd, Hg, Pb and Tl) in biological materials by isotopic dilution electrothermal-ICP-MS.⁸⁷ The samples were simply dissolved in TMAH and then underwent on-line pre-concentration based on the analyte complexation with ammonium diethyldithiophosphate and sorption of the complexes on C₁₈ bonded silica gel, prior to determination by isotope dilution ETV-ICP-MS. This analytical route was compared with that of acid digestion and both were accurate methods the simplicity of straight dissolution in TMAH is attractive.

A new approach to matrix modification in which polyhydroxy compounds (polyols) were used as complexing agents has been evaluated for the determination of trace elements (B, As, Se, Sb, Cr and Mo) by ETV-ICP-MS by Wei et al.⁸⁸ Of the eight polyhydroxy compounds studied the addition of mannitol and sorbitol had the best effect for sensitivity enhancement. The sensitivity enhancement is attributed to the fact that the polyhydroxy compounds form volatile complexes and assist in transporting the elements from the ETV to the ICP-MS.

2.2.2. Solvents. Solvent extraction continues to be of dominance in this area, it has also aided in some speciation studies. Several authors also report the effect of organic solvents on the characteristics of ICP.

Solvent extraction with N-benzoyl-N-phenylhydroxylamine has enabled the selective determination of antimony(V) by ICP-MS. The concentration of Sb^III was calculated as the difference between the total Sb content and the Sb^V content. The detection limit achieved was 0.7 ng l⁻¹.⁸⁹ The extraction of chromium(VI) from aqueous saline solutions using trioctylamine solution in toluene was studied. Quantitative recovery of Cr^VI was attained after extraction with 0.1 M extractant solution (pH 1.5) for 15 min followed by back extracting with 4 M HNO₃ and analysis by FAAS (Cr^III was not extracted under these conditions).⁹⁰ In contrast, Cr^III was determined in food via determination by FAAS after a fast oxidation of Cr^III with KMnO₄ and pre-concentration of Cr^VI in IBMK as chromium oxychloride (CrO₂Cl₂).⁹¹ Arsenic as an impurity in high-purity sulfur was determined via solvent extraction: the sample was dissolved in HNO₃ in an autoclave, and the arsenic impurity was extracted with toluene and back extracted with de-ionized water. Arsenic was determined using ETV-AAS.⁹²

The use of solvent extraction to support the development of a lead-selective electrode based on a quinaldic acid derivative has been reported by Casado et al.⁹³ Solvent extraction studies showed that the derivative of quinaldic acid 8-(dodecyloxy)quinoline-2-carboxylic acid was selective for lead(II) and copper(II) over a range of divalent and monovalent metals.

Membrane filters, in conjunction with solvent dissolution, offer another means of pre-concentration. Taguchi et al.⁹⁴ review novel techniques of membrane filtration for the enrichment and determination of trace components in water from an aspect of downsizing in analytical chemistry. One method is based on the conversion of a component in water to a hydrophobic species by chemical reaction and its retention on a membrane material. The species retained are eluted or dissolved in a small volume of a solvent. More than a 100-fold enrichment has been easily attainable by this method. Other methods, including ion-pair solid phase extraction were reviewed and the effects of functional groups in the ions and solid phase materials, the structure of the ions and the organic solvent added to the aqueous phase on the extraction behaviour are described.

Matrix effects of organic solvents in ICP-MS, ICP-AES and FAAS are reported in three papers.^95–97 The studies cover a wide variety of organic solvents e.g., acetone, methanol, ethanol, propanol, formic acid, acetic acid, propionic acid, CHCl₃, IBMK, ethylenediamine, triethanolamine, and their effects on the sensitivities on various elements are reported.

Microwave-assisted extraction (MAE) is a process of using microwave energy to heat solvents in contact with a sample in order to partition analytes from the sample matrix into the solvent. A review of this technique gives the basic principles of using microwave energy for extraction as well as some basic theory.⁹⁸ It describes the main advantage of the technique as being the ability to rapidly heat the sample solvent and, by using closed vessels, the extraction can be performed at elevated temperature, thus accelerating the mass transfer of target compounds from the sample matrix. A typical extraction procedure takes about 15–39 min and uses small solvent volumes, typically 10 times smaller than volumes used by conventional extraction techniques. The paper attempts to summarize all studies performed on closed-vessel MAE until now. The influences of parameters such as solvent choice, solvent volume, temperature, time and matrix characteristics (including water content) are discussed; all in all a very comprehensive review of MAE.

2.3. Inorganic chemicals and acids

This year there has been a more general application of analytical techniques for analysis of inorganic materials. As in previous years, solid sample analysis has been a prominent feature, with the development of a portable XRF device, several ETA-AAS studies and some interesting secondary ion mass spectrometry work being reported. ICP-MS has featured as the detection system in as many citations as ETA-AAS, ICP-OES and flame AAS, illustrating that this technique is now an integral part of today's analytical laboratory. For less-well-equipped laboratories, some novel methods have been reported for indirect analyte measurement, based on complexation or reaction of the target species with another element that can be readily detected using a lower cost analyser.

New developments in electrothermal vaporisation AAS have continued to be reported in the literature this year. A fundamental study into the comparative efficiency of pre-reduced Pd, Rh and Ru modifiers for the determination of As, Se and In in sodium sulfate has been reported.⁹⁹ Significant differences in the performance of each modifier were found, with Ru and Rh suffering signal suppression in the presence of as little as a 0.1–1 mg quantity of sulfate ion. Generally, Ru and Rh were found to be ineffective for As and In determination in sodium sulfate, whereas using a pre-reduced Pd modifier allowed As and In to be determined virtually interference free in the presence of up to 40 mg sulfate (up to 20 mg for Se). The authors suggested that the differences in efficiency were due to differences in the interaction of the modifier metals with the sulfate matrix and hypothesised that these differences would also be important for determining other analytes in sulfate media. This study highlighted the difficulties inherent in ensuring accurate analyte measurement in complex sample matrices using electrothermal vaporisation AAS.

An interesting study into the use of ETA-AAS for trace analyte measurement in a high-purity As matrix has been reported.¹⁰⁰ The relatively high volatility of the As matrix enables this matrix to be evaporated leaving the trace analytes of interest on the surface of the graphite furnace. Using this procedure, accurate measurement, free from matrix interference, could be achieved for samples containing up to 20 mg ml⁻¹ As, without the need for prior matrix separation.

An interesting method for measuring total Se in foodstuffs and biological samples, using electrothermal vaporisation AAS, has been reported.¹⁰¹ Samples were prepared by a mixed acid digestion method, followed by dilution with 20 ml of 10 M HCl. Selenium was extracted from the digests, or from standard solutions prepared in a HCl matrix, into benzene after adding HCl and KI to the sample. The benzene fraction was decanted and Co^III oxide powder was added to collect the extracted Se. Finally, the Co^III oxide powder was separated from the benzene by vacuum filtration, and the powder slurried in 1 ml of water. A portion of this slurry was introduced into the ETA-AAS, equipped with a tungsten furnace. With this procedure, quantitative interference-free measurement of Se was achieved.

A procedure for indirectly measuring I (as iodide) in iodised table salt samples, using the reducing properties of this species to reduce Cr^VI to Cr^III, in a continuous flow system, using flame AAS detection, has been reported.¹⁰² The procedure was basically a reverse flow injection method, where the dissolved sample was pumped as the carrier stream and an aliquot of Cr^VI in acidic solution was injected into it, before passing the flowing stream through a column containing a poly(aminophosphonic acid) chelating resin (selective for Cr^III). The injected Cr^VI was reduced to Cr^III in proportion to the iodide in the carrier stream and the Cr^III formed was quantitatively retained on the resin. The iodide concentration in the samples was measured via the difference in Cr^VI concentration before and after reaction with the sample. This procedure illustrates how a simple chemical reaction procedure can enhance the detection of an element and can also render this element quantifiable.

Following the theme of indirect analyte determination, a procedure has been reported for the measurement of carbon in disulfide waste water, using flame AAS.¹⁰³ In this work, samples were shaken with a diethylamine–ammonia mixture for 15 min, before addition of silver nitrate, sodium acetate buffer (pH 5.9) and chloroform. This mixture was shaken for a further 5 min during which time silver diethyldithiocarbamate formed and was extracted into the chloroform phase. This phase was back extracted with dilute nitric acid and Ag measured by flame AAS in the aqueous phase. The Ag concentration was used to determine the corresponding disulfide concentration. The results of this method compared well with those obtained using diethylamine spectrophotometry. By using a more sensitive detection system such as ICP-MS, this method could be enhanced to offer significantly improved detection limits for disulfide compared with the 1 ppm detection limit reported in this work.

An interesting application of HPLC with high temperature hydraulic, high pressure nebulisation (HT-HHPN) for matrix separation from concentrated sodium chloride solutions using flame AAS detection has been reported.¹⁰⁴ Matrix separation was achieved by complexing metal ions in the samples with trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, then trapping the complexes on a reversed phase C₁₈ HPLC column. The retained complexes were eluted into the AAS via the HT-HHPN device. This procedure was reported to be rapid (taking less than 1 min per sample) and to provide detection limits one order of magnitude better than could be achieved using a conventional nebuliser.

Several analytical procedures and studies based on ICP-AES detection have been reported this year. A method for the on-line monitoring of boron in dichlorosilane gas using ICP-AES detection has been described.¹⁰⁵ A customised sampling and gas introduction system was developed to allow direct measurements to be made from the sample gas stream. Calibration was achieved using standard additions of gaseous diborane–argon and in dichlorosilane. Using this procedure, a detection limit for B of 0.6 µg g⁻¹ of dichlorosilane was achieved.

A study into matrix effects for Zn analysis in sodium chloride using a direct sample insertion-ICP-AES technique has been reported.¹⁰⁶ In this work, the effect of the NaCl matrix on Zn vaporisation and atomisation/ionisation in the ICP was studied, under different plasma conditions and for different speeds of insertion of the sample probe. As may be expected, vaporisation losses were observed, particularly at slow sample probe insertion speed. The authors noted that introduction of a large amount of NaCl into the plasma had little effect on the ICP excitation conditions although a cooling of the plasma was observed as a result of heat loss to the sample probe.

A procedure for the determination of fluoride in aqueous samples using ICP-AES with a tungsten boat furnace vaporiser has been developed.⁸⁶ In this method, micro volumes of sample were placed inside the furnace and vaporised into atomic/molecular vapour which was subsequently transported to the plasma. Loss of fluorine, which would occur during the sample drying stage, was suppressed by adding tetramethylammonium hydroxide into the furnace vaporiser as a chemical modifier prior to analysis. A detection limit (3σ) of 6.3 µg of fluoride was achieved, using a non-resonant fluorine emission line (at 685.602 nm), rather than using resonant lines (which lie at wavelengths less than 100 nm). The method was successfully applied to leachings from fluorocarbon polymer samples.

The adsorption behaviour of heavy metal ions on nanometer sized TiO₂ particles has been studied, with a view to using this medium as a multi-element solid phase extractant, using ICP-AES as the detection system.¹⁰⁷ The elements Cu, Cr, Mn and Ni were selected as test elements and their adsorption pH curves, adsorption isotherms and adsorption capacities were studied. Adsorption rates of >90% were obtained for all the elements studied, at pH 8–9. Quantitative elution of the analytes from the material was achieved using 2 mol dm⁻³ HCl. It was found that the nanometer TiO₂ substance had a higher adsorption capacity than the more commonly used SiO₂ substrate, for the elements studied. The method was successfully applied to trace element separation from environmental samples.

The application of multi-collector ICP-MS, as an alternative to the more labour intensive TIMS technique, has continued to increase this year. The technique has been applied to the measurement of Os isotope ratios and for Os–Re isotope dilution studies down to the picogram level.¹⁰⁸ Os in the samples was first equilibrated with ¹⁹⁰Os enriched tracer in a medium that converted the Os present to OsBr₆²⁻. This was dissolved in H₂SO₄, and the solution transferred to an apparatus for evaporative introduction of OsO₄ into the plasma, using an Ar carrier stream. Measurements made using the Faraday detectors of the instrument yielded precision values of <0.02% RSD and were in good agreement with those of a negative TIMS measurement. Measurements made using the ion multiplier detectors of the instrument agreed well with those made on the Faraday detectors. Re measurements were performed using ¹⁸⁵Re as the tracer isotope and Ir for in-run mass fractionation correction. For this part of the work, the Re isotope pair were measured on ion multipliers, while the Ir isotope pair were simultaneously measured on Faraday cups. Re could be detected down to 0.2 pg with a measurement precision of better than 1% RSD.

Selenium speciation has been studied in enriched and natural samples, using both HPLC-ICP-MS and HPLC-ESI-MS.¹⁰⁹ The samples were first subjected to hot water and enzymic (protease) extractions, before being introduced onto a reversed phase HPLC column. A mobile phase containing trifluoroacetic acid or heptafluorobutanoic acid was used. The method was applied to various Se-enriched plants, including yeast, onion, garlic and hyperaccumulative phytoremediation plants and the results compared with those of natural samples. Methods of this kind can be expected to increase in future as further research into the use of plants as a means of decontaminating land is carried out.

The technique of fast atom bombardment mass spectrometry continues to find new applications, and in a publication this year, the technique has been used (in negative ion mode) to characterise the large number of silica complexes formed when silica is dissolved in sodium chloride solution.¹¹⁰ The method was sufficiently sensitive to detect less than 0.6 mM of silica, and so could be applied to silica speciation in natural waters. This approach, although based on a measurement technique that is not the most user friendly, illustrates that there are other methods that have the potential for elemental speciation, and may prove useful in future studies.

An interesting approach to measuring ⁷Li/⁶Li ratios in aqueous samples using resonant Doppler-free two-photon diode laser AAS in a low-pressure graphite furnace has been reported.¹¹¹ By using the difference in the resonant absorption energies of the two Li isotopes, ratios could be measured that agreed within the measurement uncertainty with the results obtained using a wavelength modulation diode laser AAS method. Detection of Li to levels below 1 pg could be achieved for both isotopes. This method, as with a similar method described in this review last year, offers a cheaper, mass discrimination-free alternative to mass spectrometric isotope ratio methods, but is limited to isotopes systems that have a large relative mass difference as only these possess a currently detectable difference in resonant absorption energies.

The techniques of secondary ionisation mass spectrometry (SIMS) and synchrotron XRF have been compared for measuring Au in sulfide materials in a publication this year.¹¹² The two methods were evaluated in terms of the instrumental requirements, analysis time, sample size and detection limit. Since the samples were inhomogeneous with respect to their Au distribution, making a direct comparison of the two methods was difficult. However, analysis of the same grains of an arsenopyrite sample showed reasonable agreement. The work highlighted the surface imaging and sub-ppm detection capabilities of SIMS, but also illustrated the difficulties in making accurate quantitative measurements with this technique. Synchrotron XRF, on the other hand, offered relatively simple results spectra and less matrix dependent quantitation compared to SIMS, although the detection limit was restricted to around 50 ppm because of the background signal from the As Kα emission. However, the authors stated that use of a more intense synchrotron source would decrease the detection limit to around 15 ppm.

The development of a portable XRF instrument, incorporating an ²⁴¹Am X-ray source and a Peltier cooled Si-PIN photodiode X-ray detector, has been reported this year.¹¹³ The instrument was used to non-destructively analyse the composition of a blue inorganic colorant in a 17th century Japanese votive picture. The device identified Ca, Fe, Co, Ni and As as the major elements in the colorant, which could subsequently be identified as a material called ‘smalt’. With continuing reduction in the size and weight of such instruments and enhancement in their analytical capabilities, it can be expected that portable XRF instruments will find increasing applications for samples which are either difficult to dissolve or for which non-destructive analysis is required. The technique of sonoluminescence has been applied for the determination of Na, Ca and Mg in table salt and NaCl solutions.¹¹⁴ Sonoluminescence is the emission of light by imploding bubbles formed in a liquid excited by sound of ultrasonic frequency. Ultrasound can produce temperatures of several thousand degrees or more and pressures of several atmospheres as the tiny bubbles implode. The technique has been used for accelerating chemical reactions for several years and more recently for measuring element concentrations on the basis of the intensity of the emitted light. The performance of this novel technique is improved over that of other techniques such as flame AAS because, unlike these methods, substantial sample dilution is not required. Measurement of Ca and Mg at concentrations exceeding 10 g L⁻¹ in these samples could be achieved.

Other methods of analysis of inorganic analysis have also received some attention this year. Differential-pulse anodic stripping voltammetry (DPASV) using a hanging mercury drop electrode has been used for the determination of trace Mn²⁺ in non-buffered chloride solutions, using cyanide as a masking agent. Determination of Mn²⁺ using DPASV is severely interfered with by intermetallic compound formation with Ni²⁺, Co²⁺, Cr³⁺, Zn²⁺ and Cu²⁺, but by addition of cyanide (to preferentially form cyanide complexes), interference from these elements if they are present below 20 ppb (75 ppb for Cu and Zn) can be avoided. The method was successfully applied to the measurement of Mn in tap water samples and good agreement with the results using flame AAS was obtained.

Differential-pulse polarography has been used for the simultaneous determination of Zn and Mn in commercial sodium salts, mineral waters, human hair and environmental liquid and solid waste samples, following preconcentration of their 2-(2-pyridylazo)-5-diethylaminophenol chelates using ammonium tetraphenylborate naphthalene adsorbent.¹¹⁵ Samples were dissolved or digested as required, complexed with the chelating reagent, then separated from the sample matrix and preconcentrated by passing through a plastic, syringe-type cartridge containing the adsorbent. The analytes of interest could be rapidly and quantitatively preconcentrated, at pH values between 7.5 and 11.0, by a factor of up to 75 at sample flow rates through the adsorbent of up to 10 ml min⁻¹. Detection limits in the final analytical solution eluted from the adsorbent were 30 ppb and 50 ppb for Zn and Mn, respectively. The procedure was validated by measuring NIES certified reference hair, chlorella and tea leaf materials. Electrochemical methods such as this offer the potential for rapid, selective and inexpensive analyte measurement, but are limited by serious matrix effects and poor detection limits.

2.4. Nuclear materials

Inductively coupled plasma mass spectrometry, in each of its variants, is the dominant technique in the application of analytical atomic spectroscopy to the analysis of nuclear materials. Accelerator mass spectrometry also features strongly this year due to the publishing of the proceedings of the 8th International Conference on Accelerator Mass Spectrometry, Vienna (1999).

The measurement of Pu and U at background environmental levels has been reported using multi-collector ICP-MS,¹¹⁶ double-sector ICP-MS¹¹⁷ and quadrupole ICP-MS with a collision cell.¹¹⁸ These measurements, whether for identification of the isotopic composition or as part of an isotope dilution scheme, require ‘high precision’ isotope ratios. These reports provide a good indication of the current state of the art in isotope ratio measurements by ICP-MS of nuclides present at the femtogram to attogram level.

Plutonium isotope ratios were determined across four orders of magnitude (100–600 fg cm⁻³ total Pu) using a multi-collector ICP-MS.¹¹⁶ To obtain a precision of better than 1% at these low concentrations, a double-spike technique was used. This was based upon an equal-atom ²³⁶U∶²³³U spike. This spike was used as a dual-purpose internal standard, i.e., to correct for drift in signal intensity and for changes in the mass bias of the instrument. A low-uptake nebulizer was used to enable a complete analysis on ca. 1 cm³ of sample solution. The precision obtained for ²⁴⁰Pu∶²³⁹Pu ratios of ca. 0.18 were better than 1.4% and 0.3% (2 s) at 100 fg cm⁻³ Pu (²³⁹Pu = 80 fg cm⁻³) and 3000 fg cm⁻³ Pu, respectively.

Isotope dilution and sector field ICP-MS was applied to the determination of Pu at environmental levels.¹¹⁷ A chemical separation of Pu from U, using extraction chromatography (75% yield), was required to reduce the interference of ²³⁸UH⁺ on ²³⁹Pu⁺. Sample consumption was <1 cm³ and limits of detection for ²³⁹Pu of 16 fg cm⁻³ (37 µBq cm⁻³) were reported for a real sample solution. The concentration of ²³⁹Pu in the local atmosphere was determined to be 50 ± 30 ag m⁻³ (115 nBq m⁻³).

Uranium isotope ratios, and specifically the ²³⁶U∶²³⁸U ratio, were determined in soil samples from the Chernobyl region. This ratio is indicative of irradiated uranium as ²³⁶U, formed in reactors by neutron capture from ²³⁵U, is present normally only at very low relative abundance’s in natural uranium. A quadrupole ICP-MS, a collision cell (He collision gas), shielded torch and either an ultrasonic or a concentric nebulizer were used for these measurements. Sensitivities of up to 27 GHz ppm⁻¹ were obtained for ²³⁸U⁺, UH⁺∶U⁺ ratios of 2 × 10⁻⁶ and limits of detection of 3 fg cm⁻³ of ²³⁶U in 10 ng cm⁻³ of U, corresponding to a ²³⁶U∶²³⁸U ratio of 3 × 10⁻⁷. The precision of ²³⁵U∶²³⁸U and ²³⁵U∶²³⁸ isotope ratios in a 10 ng cm⁻³ U standard were, respectively, RSD = 0.13 and 0.33% (concentric nebulizer) and RSD = 0.45% and 0.88% (USN). The isotopic composition of all investigated Chernobyl soil samples differed from natural uranium, suggesting the presence of irradiated uranium, e.g., ²³⁶U∶²³⁸U = 10⁻³ − 10⁻⁵. Results from quadrupole ICP-MS with collision cell and those obtained from a sector field ICP-MS agreed within experimental uncertainty.

Deep repositories have been proposed for the management of spent fuel. These facilities may, in the future, become exposed to groundwaters. It has been suggested that the generation of oxidizing species, by radiolysis at the near surface of the fuel, could enhance dissolution rates of UO₂. The radiolysis is generated by alpha-decay of long-lived actinides. This behaviour was studied by doping UO₂ pellets with a short-lived alpha-emitter (²³⁸Pu) and leaching of these pellets with distilled water.¹¹⁹ The leachates were analysed by standard radiometric techniques and by coupled HPLC-ICP-MS. For short lived isotopes, the limits of detection were up to 2 orders of magnitude lower for the radiometric measurements when compared with HPLC-ICP-MS. However, the sample preparation and count times were reduced for HPLC-ICP-MS and did not require multiple methods to determine the desired suite of isotopes. A similar approach, based upon coupled HPLC-ICP-MS, was used as a means of controlling spectral and non-spectral interferences for the determination of U and Th isotopes in industrial ores.¹²⁰ Quantification was obtained by external calibration and post-column internal standardization. Validation of the method was achieved by comparison with an isotope dilution scheme.

Accelerator mass spectrometry was applied to the measurement of ¹⁴C and ¹²⁹I in a number of environmental materials. Sample preparation procedures for the determination of ¹²⁹I in environmental samples and associated quality control issues were discussed.¹²¹ These were applied to the analysis of pre-nuclear soils, thyroid glands and natural waters in Lower Saxony (Germany). Although very low abundances of ¹²⁹I were observed in the thyroid glands, these were higher than the pre-nuclear equilibrium ratios in the marine hydrosphere. This suggested contamination of the samples had occurred. The data from soils and in precipitation were used to estimate pre-nuclear and modern ¹²⁹I deposition rates. A related paper, from the same group, compared the determination of ¹²⁹I by AMS and RNAA with emphasis on quality control and detection capabilities in environmental materials.¹²² The levels of ¹⁴C and ¹²⁹I in sea-water samples (500 cm³) from dump sites in the NE Atlantic, Arctic and NW Pacific were also measured by AMS.¹²³

The status of plutonium measurements by AMS at Lawrence Livermore National Laboratory (LLNL) was discussed.¹²⁴ Current backgrounds, using standard radiochemical protocols for the preparation of the targets, were estimated at 2 × 10⁷ atoms with the anticipation that on-going upgrades would reduce this to <10⁶ atoms. Recent measurements of ²³⁹Pu + ²⁴⁰Pu, ²⁴¹Pu and ²⁴⁰Pu∶²³⁹Pu ratios agreed with IAEA reference values, alpha-spectrometry and recent ICP-MS results. The application of AMS to the determination of actinides, and specifically ²³⁶U in sea-waters containing 3 ng cm⁻³ total U was reported.¹²⁵ This isotope is characteristic of irradiated uranium and could therefore be used for non-proliferation studies.

Technetium measurements using AMS were reported by the groups at ANU¹²⁶ and LLNL.¹²⁷ Similar issues were raised by both groups, i.e., the lack of a stable isobar, interference from the ⁹⁹Ru isobar and the subsequent demands on purification. Suggested solutions to these problems included: the use of a rhodium-103 tracer and a mathematical correction for the contribution of ⁹⁹Ru based upon measurement of ¹⁰¹Ru.¹²⁶ Current backgrounds are ca. 10 µBq (10⁸ atoms), mainly limited by the ⁹⁹Ru blank, although this was sufficient to allow the determination of ⁹⁹Tc in environmental samples and IAEA-381 ‘Irish Sea Water’.¹²⁷

Laser ablation ICP-MS was used to determine long-lived radionuclides in a variety of materials, e.g, geological, concrete and reactor graphite.¹²⁸ Synthetic laboratory standards were prepared for graphite and concrete whilst CRMs were available for geological materials. A number of calibration protocols were adopted, e.g., relative sensitivity factors, direct calibration and solution standards introduced via a dual sample introduction system (LA/USN). Limits of detection in a concrete matrix were ca. 50 pg g⁻¹ (²³⁷Np) using quadrupole mass spectrometry and 1 pg g⁻¹ (²³³U) using sector mass spectrometry. The precision of isotope ratio measurements were not degraded significantly when compared to solution nebulization, e.g., ²³⁴U∶²³⁸U in reactor graphite, RSD = 1.1%.

Table 2 Summary of analyses of chemicals

Element	Matrix	Technique; atomization; analyte form^a	Sample treatment/comments	Ref.
a Hy indicates hydride and S, L, G and Sl signify solid, liquid, gaseous or slurry sample introduction, respectively.
Petroleum and petroleum products—
As	Thermally cracked gasoline	AA;ETA;L	The addition of nickel nitrate as a matrix modifier enabled the determination of As in thermally cracked gasoline in a simple and rapid manner. LOD of 10 ng g^−1 was achieved	50
Hg	Natural gas liquid condensate	AA;ETA;L	Carbon adsorption is used to pre-concentrate the Hg and the sample is introduced into the graphite tube as a slurry	53
Hg	Naphtha	AA;ETA;L AFS;TD;L	The paper reports the study conducted to assess the AFS and AAS as analysis tools for the determination of Hg in naphtha. It concludes that both techniques are statistically equivalent	51
N, S	Refinery liquids	AE;GC;L	The paper details the optimization of the GC-AES system which makes 10–100 fold improvements in sensitivity	49
Mn	Gasoline	AA;QF;L	Methylcyclopentadienylmanganese tricarbonyl (MMT) has been determined by a pre-concentration system based on SPME and detection by quartz furnace AAS after thermal desorption from a micro-extraction fibre	47
Various	Diesel oil	AE;GC;L	The simulated distillation for C, H, S, N and Cl in petroleum fractions by capillary GC-AES was studied to assess the effects of split stream sampling detection	129
Oils, fuels and crude oil fractions—
Ag	Used lubricating oils	AA;ET;L	Three methods for the determination of trace amounts of silver in used lubricating oils are discussed. All procedures had similar detection limits but the emulsification method allowed a higher throughput. All experimental details and comparative results are given	66
Ba, Ca	Lubricating oil additives	AA;AF;L	Reports the use of emulsion sampling for the analysis	130
C (isotopes)	Asphaltene pyrolysates extracted from biodegraded crude oils	MS;GC;L	Carbon isotope determination has been used as a tool to develop effective oil-source tools specifically for the biodegraded oils from the Liaohe Basin, China. Details given	70
Cr	Lubricating oils	AA;ETA;L	The sample is emulsified on-line and introduced into the ETAAS system by flow injection. Experimental details are given. LOD of 6 ng g^−1 was achieved	67
Hg	Crude oil	AF;-;G	A simple lab based system based on thermal decomposition for the one-step determination of mercury is reported. The analysis requires no sample pre-treatment with chemicals or digestion procedures	68
Ni, V	Crude oil	AA;ETA;L	The direct determination of Ni and V in crude oil is explored	131
S	Fossil fuel	MS;ETV-ICP;L	ETV was used to generate a water free aerosol to minimize the ^16O^2+ ion interference on ^32S and nitrogen was used as an oxygen scavenger in the argon plasma to further minimize non solvent oxygen sources. These steps enabled the accurate determination of S in fossil fuels using isotope dilution	64
Sb, Sn	Used lubricating oils	AA;ETA;L	A graphite tube treated with Ru as a permanent modifier was used in this analysis. The samples were introduced as micro-emulsions and aqueous standards were used for calibration. Sub µg l^−1 detection limits for each element were estimated	65
Various	Biomass fuel	MS;ICP;L	Two digestion routes using mg sample sizes are compared. 17 elements were determined, the results are detailed	63
Various	Residual fuel oil	MS;ICP;L	The paper describes the developmental use of microwave digestion (closed system) to facilitate routine analysis and reproducible results	62
Various	Graphite	AE;ICP;L	The impurities and the content of the most important elements in the matrix graphite and its raw materials in spherical fuel element of 10 MW HTR were studied by ICP-AES	132
Various	Industrial waste oils	AA;ETA;L	Gaseous and liquid fractions were obtained from pyrolysis. The liquid fractions were analyzed for metals after digestion. Levels of some metals were reduced in the liquid fraction (cf., the original material)	133
Various	Lubricating oils	AA;F;L	This paper describes the behavior of a single bore high-pressure nebulizer as a tool for the analysis of lubricating oils by AAS	134
Various	Residual fuel oil	MS;ICP;L	This paper compares closed pressurized and open reflux vessel digestion systems for trace elements in residual fuel oil. The comparative results are discussed in detail	61
Coal—
As, Mn, Pb and Se	Coal	MS;ETV-ICP;L	The coal was prepared as a slurry prior to injection into the graphite tube. 10 µl of a 4.0 mg local slurry using 3 µg of Pd as a modifier was injected and the slurry was maintained using an ultrasonic probe into the sample cup just before injection. The paper reports no carrier has to be added other than the Pd	60
As, Cr and Ni	Coal, fly ash	AE;ICP;L	The concentrations of As, Cr and Ni and their speciation were discovered by chemical fractionation using a sequential leaching procedure; details given	135
C	Coal, ash	XRF;-;S	A rhodium side-window tube was used for C Kα excitation and a synthetic multiplayer crystal. The samples were presented as pressed pellets	136
Hg	Coal	AF;VG;G	The paper details descriptions of a fully automated system for the determination of Hg based on continuous flow vapour generation AFS, including sample preparation details	59
Si	Coal, siliceous materials	AA;F;L	The fusion technique was used as the sample preparation for the samples prior to analysis. Sample size versus Si content was studied as well as with and without ashing prior to fusion	137
Various	Coal	MS;ICP;L	Two semi-quantitative methods are compared to one fully quantitative method for the analysis of the rare earths. The results are in good agreement	55
Various	Coal	MS;ICP;L AES;ICP;L	Various sample digestion techniques and the impact of varying sample size has been investigated and reported, using both ICP-MS and ICP-AES	54
Various	Coal	XRF;-;S	An EDXRF instrument which has radioisotope sources instead of an X-ray tube has been evaluated. It reports a better precision for the new system	57
Various	Coal	LIBS;-;S	A new instrument variation on laser induced breakdown spectroscopy is evaluated in the paper	56
Various	Coal	XRF;-;S	XRF was used as a reference technique to use in establishing the application of dual energy gamma-ray methods to predict ash content	58
Organic chemicals—
Ag	Standard alloy	AA;F;L	Amberlite XAD-16 resin was used to pre-concentrate Ag from a thiocyanate complex of silver. A pre-concentration factor of up to 75 was achieved	73
As, Hg, Pb	Chinese mineral medicine	AE;ICP;L	Total leachable As, Hg and Pb were determined after mimicking the stomach conditions, i.e., various HCl strengths and temperatures	138
Au, Pd, Pt	Anti-cancer drugs, catalysts	AE;ICP;L	Quinine loaded resin was used to study the adsorption behavior of Au, Pd and Pt. Conditions are detailed, and the method was successfully applied to anti-cancer drugs and catalysts	139
B	Tablets	AE;ICP;L	The indirect determination of benzhexol in tablets is achieved via its precipitation with excess of sodium tetraphenylborate, and the subsequent determination of boron in the filtrate	140
Ba, La	Aqueous solution	AE;ICP;L	A new method for the separation of lanthanum(II) and barium(III) as their thenoyltrifluoracetone (TTA) complexes with dibenzo-18-6 (DB18C6) in o-dichlorobenzene has been established	76
Cd, Se, Zn	Anti-dandruff shampoo	AA;F;L AE;ICP;L	The samples were digested with HNO3 in a closed microwave digestion vessel which was irradiated at 800 W for a few minutes. The results obtained compared favourably with traditional sample preparation methods	141
Cd	Drinking water	FI-AE;ICP;L	For the retention of Cd, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) and Amberlite XAD 16 were used at pH 9.5	72
Cu	Standard steels, mussels	FI-AA;F;L	The process of on-line sorbent pre-concentration using 1-nitroso-2-naphthol as a complex agent for the determination of Cu is reported	78
F	Fluorocarbon polymer, aqueous solutions	AE;TBF;G	A tungsten boat furnace (TBF) vaporizer system coupled to an ICP-AES was used for the determination of fluorine. Tetramethylammonium hydroxide solution was added in the TBF as a chemical modifier to prevent fluoride loss. The wavelength used was 685.602 nm and the experience of others enabled successful determinations to be made	86
Fe	Activated charcoal	AA;F;L	The study characterized the adsorptive capacity of activated charcoal for ferrous sulfate at 3 pH environments	142
Hg	Chinese herbal medicine	AE;ICP;L	Powered samples (1 g) were evaporated until fuming with HClO4	81
Hg	Chinese medicine	AA;CV;L	Powdered samples (0.1–0.5 g) were digested using microwave digestion and HNO3	85
Mn	Spring, well and tap water	AA;ETA;L	The applicability of hydrated iron(III) and dithiocarbamates as colloid collectors for flotation pre-concentration of Mn is discussed fully in the paper. A detection limit of 0.025 µg l^−1 was achieved	80
Ni	Standard steels, mussels	FI-AA;F;L	The process of on-line sorbent pre-concentration using dimethylgloxime as a complexing agent for the determination of Ni is reported	77
Pd	Synthetic and real samples	AA;F;L	Pd is absorbed onto 1,5-diphenylcarbazone (DPCO) from a large volume of its aqueous solution, improving the achievable detection limits	79
Rb	Chinese medicine	AA;CV;L	Samples (0.2 g) were decomposed with HNO3, HCl, HF and H2SO4	143
Se	Selenium nutritional supplements	MS;ICP;L	A HPLC column with a chiral crown ether stationary phase and a mobile phase of 0.10 M HCLO4 was used to separate selenoamino acids prior to determination by ICP-MS	144
SO4	Sodium dimethyl-1,3-phthalate-5-sulfonate	AA;F;L	An indirect method of determining SO4via the addition of various chemicals which results in a Cu complex is reported	145
Various	16 Chinese medicines	AA;F;L	Powered samples (2 g) were digested with HNO3–HClO4	82
Various	Heroin	AE;ICP;L	The samples were microwave digested with HNO3. The samples were introduced into the ICP using an ultrasonic nebuliser	83
Various	Various water samples	MS;ETV-ICP;L	An investigation into the effect on sensitivity enhancement of eight polyhydroxy (polyols) compounds is reported. The study included an examination of interferences arising from Ca, Mg, K and Na from the water	88
Various	Thiosalicylic acid immobilized Amberlite XAD-2	AA;F;L	The metal sorption behaviour and applications in estimation of metal ions of thiosalicylic acid immobilized Amberlite XAD-2 using AAS are detailed	71
Various	Coal	XRF;-;S	An EDXRF instrument which has radioisotope sources instead of an X-ray tube has been evaluated. It reports a better precision for the new system	57
Various	High purity iron	MS;ICP;L	Impurities were extracted by the use of SFE, using bonded silica with octadecyl (C18) as the solid phase sorbent	36
Zn	Biological materials, pharmaceutical formulations	AA;F;L	A spectrometric method based upon the reaction of Zn^II with 2,2′-dipyridyl-2-pyridylhydrazone (DPPH) giving rise to a yellow coloured complex, was developed as a rapid, simple, low cost method. The results compared well with those attained by FAAS	146
Solvents—
As	High purity sulfur	AA;ETA;L	The As impurity was extracted by firstly dissolving the high purity sulfur in nitric acid, and extracting the As in toluene, then back extracting into water prior to analysis	92
Au	Waste water	AE;ICP;L	A solvent sublation study for the determination of trace Au^III, Pt^VI and Pd^II in waste waters is described in detail	147
Cr^VI	Soil	AA;F;L	The solvent extraction of Cr^VI in soil using trioctylamine solution in toluene is reported	90
Cr	Foods	AA;F;L	Cr^III was determined after fast oxidation with KMnO4 and pre-concentration of Cr^VI in IBMK as chromium oxychloride	91
Hg	Organic solvent	AA;THFA;L	The use of the transverse-heated filter atomizer (THFA) is described in detail for the analysis of Hg in both organic solvents (IBMK) and aqueous solutions	148
Hg	Biological samples	MS;ICP;L	The matrix effects of organic solvents, e.g., ethanol, propanol, glycerol, etc., on the signal intensity in ICP-MS has been studied and reported	95
Ir^IV	Hydrochloric acid media	AE;ICP;L	Trace amounts of iridium are quantitatively extracted from hydrochloric media via the use of crown ether, forming an ion-association complex of iridium hexachloro anion IrCl6^2− with dicyclohexyl-18-crown-6 (DC18C6) oxonium cation in chloroform	149
Pb	Fine particulates	AA;ETV;L	The fine particulates were suspended in various solvents before analysing. The behaviour of the suspension in various solvents was studied using a particle size analyser	150
Pb	Biological samples	MS;ICP;L	As for Hg	95
Pd	Waste water	AE;ICP;L	As for Au	147
Pt	Waste water	AE;ICP;L	As for Au	147
Rh	Nitric acid, sodium trichloroacetate media	AA;F;L	The paper reports on the successful extraction of trace amounts of Rh from nitric acid and sodium trichloroacetate media using ion-association complex of hexahydrated rhodium cation Rh(H2O)6^3+ and the trichloroacetate. The effects of various factors are discussed, including solvent	151
Sb	Natural water	MS;ICP;L	N-Benzoyl-N-phenylhydroxylamine was used to selectively extract Sb^III from natural waters. The total Sb and and Sb^V were then determined and Sb^III calculated by difference	89
Sr	Biological samples	MS;ICP;L	As for Hg	95
Inorganic chemicals and acids—
Ag	Telluride monocrystals	AA;ETA;L	Samples dissolved in dilute HNO3 or HNO3–HCl mixtures as required. Tartaric acid added as a chemical modifier	152
Ag	Road salt	AA;ETA;L	Samples dissolved in de-ionised water. Matrix separation and pre-concentration performed by co-precipitation with Co pyrrolidinedithiocarbamate. Samples then re-solubilised with a 0.2% NH4H2PO4–5% dilute nitric acid mixture	153
Ag	Silvered jewellery articles	XRF;-;S	The sample surface was cleaned before analysis	154
As	Environmental waters	AA;HG;L	Samples treated with L-cysteine and NaBH4 in a perchloric acid medium, to generate AsH3. By using different acid, NaBH4 and L-cysteine concentrations, the separate As species could be individually reacted for speciation measurement	155
As	Dilute nitric acid–hydrogen peroxide solutions	AA;HG;L	Various arsenic species were subjected to different microwave digestion procedures to study their stability. After digestion, the species were separated by reversed phase HPLC prior to detection	156
As	High purity sulfur	AA;ETA;L	Samples dissolved in nitric acid. Arsenic extracted from the solution using toluene, then back-extracted with water	92
As	Antimony trioxide	AE;ICP;L	Dried sample digested with a mixture of HCl, KCl, tartaric acid and water in a microwave oven. The digest was diluted with water prior to analysis	157
As	Hg–Cd–Te materials	MS;SI;S	None	158
As	Antimony trioxide	AE;ICP;L	Samples were decomposed with H2SO4, tartaric acid added and the mixture diluted to 50 ml. As determined after a further 1∶1 dilution; Se determined after an additional matrix separation and pre-concentration procedure	159
Au	Methyl isobutyl ketone extracts	AA;F;L	Au extracted from the sample matrix using fluorinated calixarenes incorporating lower rim S atoms, contained in supercritical CO2	160
Br	Water samples	MS;ICP;L	Samples injected into an ion chromatography system coupled to the ICP-MS and bromine detected as bromate	161
Ca	Saturated high-purity sodium chloride	AA;F;L	Samples diluted with water and the pH adjusted to 12 using 10% NaOH. Ca and Mg retained on 401 type chelate ion-exchange resin, then eluted using 3 M HCl	162
Cd	Calcium salt reagents	AA;F;L	Cd separated from the sample matrix and preconcentrated using sulfydryl cotton, then eluted using dilute acid	163
Cl (as ClO4^−)	Water samples and sulfate solutions	MS;ESI-FAIMS;L	Electrospray ionisation (ESI) used to generate gas-phase anions subsequently separated using field asymmetric waveform ion mobility spectrometry (FAIMS) and detected by quadrupole MS	164
Co	Ferrosilicon	AA;F;L	Samples dissolved in pH 2 HCl. For the AAS determination, acetone and sulfosalicylic acid were used as sensitising and masking agents (for Ca and Fe) respectively	165
Cr, Fe and Ni	Molybdenum powder	AE;dc arc;S	Sample dissolved in nitric acid to homogenise the material. Acid matrix then evaporated to facilitate analysis of the powder	166
Fe	Annealed Fe-doped LiNbO3 crystal	MS;SI;S	None	167
Ge	Zinc electrolytic solutions	AE;ICP;L	Ge complexed with 8 M HCl and extracted (as GeCl4) into xylene on-line. Organic phase separated, reacted on-line with NaBH4 in DMF–ethanoic acid to form GeH4, which was then carried to the ICP using Ar via a gas–liquid separator	168
Hg	Antimony trioxide	AE;ICP;L	As for As	157
In	Hg–Cd–Te materials	MS;SI;S	As for As	158
Ir	Hydrochloric acid solutions	AE;ICP;L	Ir^IV in the samples [as (IrCl6)^2−] reacted with a crown ether in chloroform to form an ion-association complex, before back extraction into aqueous solution for analysis	149
Mg	Saturated high purity sodium chloride	AA;F;L	As for Ca	162
Ni	Tap and spring water	AA;ETA;L	Ni removed from 1 l of the sample by co-flotation using a hydrated Fe2O3 and Fe hexamethylenedithiocarbamate mixture. The solid extract was dissolved before analysis	169
Ni	Sea-water, mussel tissue and dissolved steels	AA;F;L	Sea-water and digested samples were mixed on-line with dimethylglyoxime and the complex formed retained on a C18 sorbent in a mini-column. Complex eluted into the AAS using a 1% HNO3–ethanol solution.	77
Ni	High purity aluminium oxide and aluminium hydroxide	AA;F;L	Sample fused with K2O–H3BO3 at 1150 °C. Residue then extracted with hot water and treated with a multi-reagent aqueous solution. This solution was then shaken with dimethylglyoxime in CHCl3 and the organic phase back extracted into 10 ml of 1∶1 diluted HCl	170
O	Orthophosphate samples	MS;ESI;L	Samples prepared in aqueous solution	171
Pd	Anode slimes	AA;F;L	Pd and Pt leached from the samples using a nitric acid–tartaric acid mixture, then precipitated using Sn^II chloride, before analysis	172
Pt	Anode slimes	AA;F;L	As for Pd	172
Re	Dilute nitric acid	MS;ICP;L	Re separated from dilute nitric acid solution using an extraction chromatographic resin, then eluted into the ICP-MS	173
Rh	Chloroplatinic acid and palladium chloride solutions	AA;F;L	Samples treated with tri-n-butyl phosphate to convert Rh from the chlorocomplex to the hexahydrate cation. The ion-association complex of this cation and trichloroacetate anions was then extracted into an organic phase before back extraction and analysis	151
Sb	River water	AA;ETA;L	None. Ag used as a more effective matrix modifier for the furnace in place of Pd	174
Se	Antimony trioxide	AE;ICP;L	As for As	159
Se	Inorganic and organic selenium compounds	MS;ICP;L	Selenium species separated in the presence of pyridine on a cation exchange column, using methanoic acid as the mobile phase. A hydraulic, high pressure nebuliser was used	175
Sn	Aqueous salt solutions	AA;ETA;L	None. Studies made of the effect of different salts on the determination of Sn	176
Zn	Nickel electrolyte	AA;F;L	Zn in the samples separated from the matrix by absorption of its chlorocomplex on a mini-column containing a strongly basic anion exchanger. NaCl concentration in the electrolyte was high enough to form the Zn chlorocomplex	177
Various (4)	Hydrogenated amorphous Si–Ge alloys	MS;SI;S	None	178
Various (5)	Ni sulfide fire assay buttons	MS;ICP;S	Samples fused with NiS and the solid material produced analysed directly	179
Various (6)	Non-volatile residue of liquid phase WF6	MS;ICP;L	Residue dissolved with an aqueous ammonia, HF and HNO3 mixture and aspirated into the instrument via an inert sample introduction system	180
Various (8)	Tantalum diboride	AE;ICP;L	Samples decomposed using various acid mixtures	181
Various (9)	Silver(II) oxide	XRF;-;S	None required for XRF analysis, although samples were also dissolved in nitric acid for analysis using atomic absorption and emission techniques	182
Various (10)	High purity tantalum materials	MS;ICP;L	Samples dissolved in HF–HNO3 at 150 °C, then diluted with water. Aliquot of the sample then injected onto a strongly basic anion exchange column. Tantalum was retained and the trace elements of interest were eluted to the ICP-MS	183
Various (12)	Thermoluminescent aluminium oxide powders	AE;ICP;L	Samples microwave digested using an acid mixture	184
Various (12)	Beryllium oxide	XRF;-;S	Sample (1 g) was pressed into pellets for analysis. A Mo pad was placed between the sample and sample holder to eliminate spectral interference from the latter and to produce more emission to enhance sensitivity	185
Various (34)	Sea-water salt samples	AE;ICP;L	Samples dissolved in a buffered solution. Trace analytes then separated using a chelating ion-exchange resin and eluted with dilute acid for analysis	186
Various (35)	Fertilizer samples	AE;ICP;L	Samples ground to powder, then dissolved using different procedures based on HNO3, HCl and HF mixtures	187
Various	Emeralds	PIXE/PIGE;-;S	None	188
Various	Humic acid colloids in aqueous solution	MS;ICP;L	None. Other analytical techniques used to compare results (PIXE, INAA, etc.)	189
Various	Silica chromatography particles	AE;ICP;L	Samples refluxed with water, dilute HCl and dilute HF solutions. Elements leached into these solutions analysed using ICP-MS; elements on the surface of the particles studied using SIMS	190
Nuclear materials—
^41Ca	Concrete	RIMS; XRF	After solubilization, standard radiochemical separation of Ca using a ^47Ca yield monitor. Total Ca determined on solution by XRF. ^41Ca measured by diode laser based RIMS. LOD ∼ 5 × 10^−10 relative to total Ca	191
Pu	Urine	MS;ICP;L	Standard digestion and radiochemical separation applied with ^242Pu tracer. Internal standard added ^209Bi. LOQ ∼ 0.1 mBq dm^−3^239Pu	192
^99Tc	Various	MS;ETV-ICP;L	Matrix modifier of nitric acid–sodium chlorate used to suppress Ru interference. 1000-fold excess of Ru at 100 pg cm^−3 Tc resulted in ∼4% increase in signal at mass 99. LOD ∼ 30 fg (20 µBq)	193
^99Tc	Soil samples	MS;ICP;L	Three methodologies: (a) acid leach from ashed soil; (b) acid leach from raw dry soil; (c) volatilization using a combustion apparatus. Sample cleaned up by extraction chromatography. Absolute LOD 0.17 mBq	194
^99Tc	Chernobyl plant and soils	MS;ICP;L	Soils pyrolysed and Tc volatized/trapped. Plant samples wet ashed. Tc extracted and purified from solutions by extraction chromatography. Values of 1.1–14.8 Bq kg^−1 (soils) and 0.2–6 Bq kg^−1 (soils) obtained	195
Th	Environmental and mine tailings	MS;ICP;L	Selective extraction or total by fusion. Th concentrated on TRU.SPEC. U in waters determined after pre-concentration on Chelex 100 and purification on UTEVA	196
^232Th	Urine	MS;ICP;L	UV digestion. Quantification obtained by standard addition (SF-ICP-MS) or external calibration with aq. standards (Q-ICP-MS)	197
^233U	Th solutions	AE;ICP;L	Th precipitated as oxalate from nitric acid solution. ^233U measured at 385.958 nm line with isotope shift of 8 pm	198
^234U/^238U	Natural waters	MS;FI-ICP;L	Samples acidified and flow injected	199
^238U	Urine	MS;ICP;L	As for Th	197
U	Environmental and mine tailings	MS;ICP;L	As for Th	196
Various	Pu metal	MS;GD;S	Fragments chipped from ingot, analysed at-line	200
Various	Spent PWR fuels (15–35 GWd/TU)	AE;ICP;L	Pu separated by anion exchange from U in 8 M nitric acid, by extraction chromatography using supported TBP. Fission products separated on supported HDEHP. Precision <5%	201

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3 Advanced materials

3.1 Polymeric materials and composites

Isotope dilution mass spectrometry was used to provide SI-traceable reference values for Cd, Cr and Pb as part of the “Polymer Elemental Reference Material” (IRMM, Geel).²⁰² After decomposition in a high pressure asher, Cd and Pb were determined using ID-ICP-MS and Cr by ID-TIMS. Uncertainty budgets were estimated by propagation of uncertainties using internationally recognized guidelines and procedures. The uncertainty on the measurements were <2% relative for concentrations in the µg g⁻¹ range.

Direct solids analysis remains an important topic in polymer analysis due to the difficulty in mineralizing these materials. Radiofrequency-glow discharge spectrometry was discussed in some detail for the analysis of polymers.²⁰³ An important advantage of glow discharge ion sources is that they can be used for both atomic and molecular mass spectrometry. The determination of the elemental composition of polycarbonate films by energy dispersive XRF was validated using INAA.²⁰⁴ Calibration was obtained against cellulose pellets doped with single element compounds. Absorption corrections were derived from “thick” targets. A micro-beam XRF technique was used to produce quantitative elemental maps of polymer films.²⁰⁵ The spatial resolution was ca. 30 µm and 128 point line scan measurements were used to derive the elemental maps. The local concentrations were determined using the modified backscatter fundamental parameter method.

Laser induced breakdown spectroscopy was used for real time identification of post-consumer plastics.²⁰⁶ Spectra were obtained in a 200–800 nm window and compared with reference library spectra. This comparison was aided by simple statistical methods including linear and rank correlations. The probability of correct identification ranged from 0.8 to close to unity with most polymers tending to the latter. The potential application of laser ablation coupled to MIP-AES was investigated using a Nd-YAG at 1064 nm and either an argon or He plasma.²⁰⁷ The distinct advantage of the He MIP was that non-metals, including F and I could be detected efficiently. Estimated limits of detection for metals were in the range 1–800 µg g⁻¹ and 500–7000 µg g⁻¹ for non-metals. Memory effects were observed for high concentrations of chlorine and carbon.

A sensitive method for chlorine in polymers was based upon diode laser atomic absorption.²⁰⁸ Polymers were ablated and the volatile components separated by GC. The column effluent was coupled to a low pressure plasma that acted as the atom cell for the AAS measurement. A limit of detection for Cl of 10 pg was obtained and the method was shown to be insensitive to non-chlorinated hydrocarbons.

The identification and characterization of pigments and manuscripts continues to provide a variety of challenges in microscopic techniques. Particle induced X-ray emission spectrometry (PIXE) was applied to the classification, in terms of point of origin, of Japanese papers,²⁷⁸ manuscripts from the Otani collection,²⁰⁹ pigments from ancient Egyptian limestone wall paintings and coffin decorations²¹⁰ and white pigments from Minoan pottery.²¹¹ Laser induced breakdown spectrometry, in conjunction with Raman spectroscopy, was used for the identification of pigments from a 19th Century Byzantine icon.²⁷⁹ The important features of LIBS for this application included: that the technique was perceived to be “micro-destructive”, the ability to analyse the icon in situ minimized any potential damage to the art work and the ability to obtain a depth profile of the pigments. The latter point is extremely useful as the stratigraphy of the paint layers can be used to detect interventions from restorative work and is often characteristic of a specific artist, or school. X-ray photoelectron spectroscopy was used to measure the thickness of a fluorinated phosphoric ester based protective material for limestone monuments, buildings and artifacts.²¹²

3.2 Semiconductor and conducting materials

The determination of trace metals in semi- and superconducting materials continues to attract interest. One of the main problems with this type of analysis is that of contamination and cleaning of materials. The evaluation of cleaning efficiencies using radioactive tracers along with the development of a microwave digestion method has been reported.²¹³ The effects of solution temperatures and substrate types of various wet cleaning recipes in removing metallic impurities such as Na, Fe and Cs were studied by examining the mechanisms of the electrochemical segregation of the metallic impurities between the substrate and the cleaning solution. The authors found that the enthalpy of oxide formation and the effect of adsorption were the two main reasons for the presence of impurities in the cleaning solutions. Results showed that SC2 and DHF were effective in removing metallic impurities at 47 °C and 82 °C whereas SPM and BOE were only effective at 82 °C.

A microwave digestion method was successfully evaluated for antireflective coating and photoresist samples. Detection by ICP-MS provided detection limits in the range of ng to sub-ng ml⁻¹. Except for Ca, spike recoveries were in the range of 82–121%. A method for the determination of Cu and Si in Al target metal has been developed based around ICP-AES.²⁸ A recovery of 45% for Si was obtained using HCl wet acid digestion. The recovery was raised to 90% when a high pressure acid digestion system was used or when H₂SO₄ was used instead of HCl in the wet acid digestion method. Calibration was achieved by standard additions for three Al targets containing more than 0.2% (w/w) Si along with 0.5% (w/w) Cu. A method for analysis using 30% H₂O₂ by ICP-MS has been reported.²¹⁴ Using cool plasma operating conditions, along with a shield torch configuration, many of the common polyatomic interferences were eliminated. A range of analytes such as Na, Mg, Al, K, Ca, Cr, Mn, Fe, Ni, Cu, Sn and Pb were determined with detection limits from 0.02–4 pg ml⁻¹. Using standard additions calibration recoveries were 97–109%.

Superconductor oxides (YBa₂Cu₃O_7 − x) have been analysed for their trace metal content by ICP-AES.²¹⁵ The Mn 259.373 nm line was used to find the optimal viewing position in the plasma for the determination of Ca, Mg, Fe, Mn, Al, Ni, Si and Sr. Instrumental detection limits ranged between 0.002–0.006 mg l⁻¹ with practical detection limits of between 2 × 10⁻⁵ and 1.2 × 10⁻⁴ (% m/m). Precision ranged from 1.4 to 3.2% and depended on the element and concentration.

Obviously for this section the analysis of Si wafers for trace impurities and for dopants is of paramount importance. A study on the use of quantitative SIMS for the analysis of carbon and fluorine impurities on Si wafers stored in quartz-glass boxes equipped with polymer carrier cases (polypropylene, polybutylene terephthalate or perfluoroalkoxy polymer) has been undertaken.²¹⁶ The adsorbed organic contaminants were identified by ToF-SIMS. The concentrations of contaminants on the wafer surface were measured as a function of wafer storage positions as well as carrier case storage time. For quantitative analysis SIMS combined with the encapsulation method was employed, and ¹²C⁻ and ¹⁹F⁻ ions detected. It was found that the amount of adsorbed contaminants on the wafer surface depended not only on the wafer storage conditions but also on the carrier case materials.

The technique of vapour phase decomposition (VPD) has been used in conjunction with ICP-MS for the analysis of trace elements in Si wafer materials.²¹⁷ The VPD technique was used to dissolve the SiO layer on the Si wafer surface by exposing the wafer to HF vapour. After VPD, the hydrophobic Si wafer surface is scanned with an acidic droplet of solution to extract the surface trace metals. As ICP-MS was employed in the analysis of the acidic droplets a study was also made of the polyatomic interferences. The interference of F on ⁵⁹Co was found to be negligible and controllable. They were also insignificant for the isotopes of Ga, Cu, Ge and Ni. However, for ⁴⁷Ti, ⁶⁸Zn and ⁴⁴Ca, pronounced matrix effects were observed. Unlike 34 other elements, Ag recovery was poor due to the reduction of this element on the Si surface. An alternative extraction solution containing HNO₃ and HCl was used to collect the Ag from the Si wafer surface. A further report uses VPD along with TXRF for the trace element analysis from Si wafer samples.²¹⁸ Light elements such as Na and Al along with transition metals Fe, Ni, Cu and Zn were determined. Measurement using the W Mα line was conducted for the high sensitivity analysis of Na and Al. Through the use of VPD/TXRF, limits of detection were improved by 2 orders of magnitude when compared to the use of TXRF on its own. For 150 mm Si wafers detection limits were 3 × 10¹⁰ atoms cm⁻² for Na and 2109 atoms cm⁻² for Al. The detection limits for Fe, Ni, Cu and Zn were 4 × 10⁷, 5 × 10⁷, 6 × 10⁷ and 9 × 10⁷ atoms cm⁻², respectively. The results from the VPD/TXRF were assessed by AAS and the two sets of results were in good agreement. Studies on the glancing angle dependence of TXRF proved that the sample, after VPD treatment, became a particle type on the wafer.

A thermally stable Ni-based ohmic contact is one of the most attractive contact materials for developing superior GaAs devices. A combined grazing-incidence and grazing-takeoff XRF (GIT-XRF) method has been applied to study the interface reaction between a Ni thin film and a GaAs wafer.²¹⁹ Ni thin films (approximately 10 nm in thickness) were deposited on GaAs wafers, then annealed at 373 and 473 K. When both techniques were applied to a sample annealed at 373 K, it was not possible to recognise interface reactions between Ni and GaAs. However, the small compositional change at the interface could be detected by the non-destructive GIT-XRF method. The diffusion of Ni atoms into the GaAs substrate, which was induced by heating at 473 K for 3 min, was clearly found by measuring the takeoff angle dependencies of characteristic X-ray intensities at a grazing incidence of 2.5 mrad. Finally, the workers evaluated the mixed Ni–GaAs layer to be Ni₅GsAs with a thickness of 15 nm by fitting calculated curved to experimental plots.

3.3 Glasses

In common with previous years, a major area of interest is in surface analysis techniques. The coloration of float glass due to colloidal silver was studied using secondary ion mass spectrometry (SIMS), transmissionelectron microscopy and optical spectroscopy.²²⁰ These colloids were formed from sputtered silver films during heat treatment. The combination of analytical techniques allowed a full characterization of the glass in terms of colloid size versus depth, silver and tin depth profiles and the influence of corroded layers on the colour reaction.

Glass fibres are used to strengthen concrete and their resistance to corrosion in this highly alkaline matrix is crucial to the final product quality.²²¹Secondary neutral mass spectrometry (SNMS) and atomic force microscopy combined to characterize the corrosion properties of these fibres. It was observed that a preliminary deposition of a soft corrosion product at or close to the surface preceded the formation of a Zr-rich protective layer.

An “expert system” was used to identify the source of local defects in glasses and allow appropriate countermeasures to be taken.²²² An essential input to this database was a rigorous characterization of the defect and this was accomplished using a combination of EPMA, LA-ICP-MS and XRD.

The feasibility of converting glassy wastes into high value structural composite materials for the manufacture of brake linings included an environmental risk assessment.²²³ These waste forms were loaded with between 20–60% m/m of vitrified domestic waste residues and the potential for re-mobilization of heavy metals were assessed using leach studies to simulate the effects of weathering. The leachates were analysed using ICP-MS. Thermal shock experiments were conducted with LA-ICP-MS to monitor secondary products produced at high temperatures.

Glasses for the immobilization of high level nuclear waste were analysed using LA-ICP-MS.²²⁴ The experimental parameters that affected the accuracy and sensitivity of the determination were studied and included laser properties, transport efficiency to the ICP and optimization of the ICP-MS. A good agreement between the semi-quantitative analysis by LA-ICP-MS and the reference values for these glasses was demonstrated.

Laser ablation ICP-AES was used to obtain a depth profile of Sn coated float glasses.²²⁵ The procedure involved individual ablation cycles of a quadrupled Nd-YAG rastered over the area of interest. The peak areas of the resultant transient signals were plotted against cycle number and the ablation rate estimated by profilometry. Low laser energies were used (1–6 mJ), resulting in ablation rates of 20–90 nm per pulse and the spatial properties of the beam were improved via simple masking. This combination of rastering, low energy ablation and beam masking resulted in an almost uniform removal of material. The depth profiles of graded structures agreed qualitatively with SIMS measurements. The acoustic emission from the ablation events were also monitored and similarly followed the behaviour of the atomic emission.

Art, archaeometry and forensic investigations continue apace. The use of µ-XRF techniques for the characterization and provenance of artifacts included applications to historic glasses.²²⁶ Multi-element fingerprints of a number of 18th century glass vessels, aided by a multivariate statistical analysis, allowed the grouping of these vessels according to their place of manufacture.²²⁷ The application of LA-ICP-MS was described as a “new tool” to characterize archaeological materials and the results of these analyses compared with those obtained by competing and complementary technologies.²²⁸

The forensic discrimination of glasses by their elemental composition, as determined by ICP-MS, continues to provide an exemplary lesson in rigorous control of analytical quality. The reliability of using elemental composition as a means of distinguishing glass fragments was tested by the use of statistical techniques, e.g., ANOVA.²²⁹ This was coupled with an assessment of accuracy. The statistical analysis apportioned variance between components of time (day-to-day), dissolution (sample-to-sample), calibration and instrumental (internal). This initial analysis included 68 isotopes representing 57 elements. When combined with an appreciation of analytical bias, this allowed the classification of the analytical data into four groupings. Those elements not falling into the classification of both good precision and accuracy (RSD and bias <10%) were examined critically before inclusion in a list of potentially discriminating elements. This list, consisting of 59 isotopes representing 46 elements, provides the input to a database for float glasses. In a similar task, ICP-MS and refractive index (RI) measurements allowed the forensic discrimination of bottle glasses.²³⁰ Thirteen elements were found to have some utility in the discrimination of bottle glasses and could be determined with a precision of RSD < 3.2% (excluding Sn and Pb) in a CRM (NIST 612). The proposed method was applied to 16 bottle glass samples assembled into a matrix of 120 pairs. Thirteen pairs were indistinguishable by RI measurements but all were distinguishable by the combination of techniques.

3.4 Ceramics and refractories

In previous years many abstracts and reports were received by the reviewing team concerning the problems of determining rare earth elements in their oxide matrices, mainly by Chinese workers. However, either due to this subject receiving less attention this year, or to our new abstracting system, the number of reports on this subject has been severely reduced. Therefore, readers will notice that the summary of ceramic materials normally provided in Table 3 has a different emphasis this year.

Table 3 Summary of analyses of advanced materials

Element	Matrix	Technique; atomization; presentation^a	Sample treatment/comments	Ref.
a Hy indicates hydride and S, L, G and Sl signify solid, liquid, gaseous or slurry sample introduction, respectively.
Polymers and composites—
Cd	Waste plastics	XRF, AA, AE;ICP;L	Microwave and open beaker digestion compared. No statistical difference observed between methodologies with exception of wet ashing with sulfuric acid	253
P	PET and PolyProp	AA;ETV;S	Direct solid sampling of material. Pd–ascorbic acid modifier used. LOD = 2.5 µg g^−1	254
Pb	Waste plastics	XRF, AA, AE;ICP;L	As for Cd	253
Sb	Waste plastics	XRF, AA, AE;ICP;L	As for Cd	253
Various	Document paper	MS;ICP;L	Microwave digestion with nitric acid –hydrogen peroxide. Nine discriminators selected to allow forensic identification of paper	255
Various	Photoresist	MS;ICP;L	Microwave digestion, recovery = 88–128% (excl. Ca)	256
Semiconductor and conducting materials—
Various	Si wafers	TXRF;S	Low-Z elements were determined using the PTB plane grating monochromator beamline for undulator radiation at the electron ring BESSY II. For droplet samples on Si wafers DLs for Na down to C were in the low pg range	257
Ceramics and refractories—
Co	WC	AE;LA-ICP;S	Co coatings were ablated using a Nd:YAG laser at 266 nm (10 Hz, 10 mJ per shot). Non-linear dependencies were observed which were overcome using W as an internal standard	258
Na	Al2O3	AA;F;L	Sample (0.2–0.5 g) was fused in a Pt crucible with Li2CO3 (0.7 g) and H3BO3 (1 g) at 800–1000 °C. The fusion was dissolved with 50% HNO3. CsCl was added and recoveries were 98–102% with RSD of <3%	259
Various (5)	SiN	MS;LA-ICP;S	Samples was subjected to a Nd:YAG laser (150 mJ, 1064 nm). Lased particles were trapped in a 0.1 M HNO3 solution which was analysed for Mg, Ti, Mn, Co and W by ICP-MS. Particle transport efficiency was about 7%	260
Various (8)	TaB2	AE;ICP;L	Sample (0.25 g) were decomposed by HF and HNO3 at 160 °C in PTFE bombs. Boric acid was added before determination of Ca, Co, Cr, Fe, Mg, Nb and W. DLs ranged from 0.03 (Mg) to 6.3 (W) µg g^−1	181
Various (6)	Al2O3	AE, MS;ICP;L	Microwave digestion was evaluated using HCl, HNO3, H2SO4 and H3PO4. Spectral interferences on Fe, Ga, Mg, Mn, Na and V were studied and results checked using SRM699	261
Various (14)	Y2O3	AE;ETV-ICP;S	A PTFE emulsion was used as a fluorinating agent which minimised matrix effects. REE DLs ranged from 0.032–2.52 ng with RSDs of 1.3–4.3%	262
Various (14)	CeO2	AE;HPLC-ETV-ICP;L	Rare earths were separated from Cs by HPLC using 2-ethylhexyl hydrogen 2-ethylhexylphosphate (P507) resin and a dilute HNO3 mobile phase. Separation was obtained within 60 min	263
Various (24)	Al2O3	MS;ICP;L	Sample were dissolved by H2SO4 in PTFE pressure vessels. Most interferences were avoided using a resolution of 5000. Standard conditions were employed to overcome matrix effects	264
Various (5)	SiC	AE;ETV-ICP;Sl	Sample (100 µg) was ashed in the presence of PTFE at 800 °C producing 97% decomposition. DLs of 0.3 (Al) to 0.08 (Cu) µg g^−1 and precisions of 6–2.8% were obtained	265
Various (7)	Si3N4	AE;ICP;Sl, L	Samples were dissolved by high-pressure acid digestion (HF∶H2SO4 (1∶1)). Significant differences between aqueous and slurry samples were observed	266
Various (4)	Al2O3 ceramics	AE;ETV-ICP;Sl	A PTFE emulsion (600 µg) was used to promote vaporisation for Fe, Cu, Cr and V. DLs of 0.3 (Fe) to 0.08 (Cu) µg g^−1 were obtained with repeatability of <10%	267
Catalysts—
As	Pd chloride	AA;ETV;L	Sample (0.5 g) dissolved in 6 M HCl, diluted to 100 cm^3, aliquot (2–4 cm^3) treated with ascorbic acid + 2 cm^3 6 M HCl and diluted to 10 cm^3. 10 µl injections. LOD=5 ng cm^−3	268
Al	Alumina supported NiO catalysts	AA;XPS;S	An improved catalyst was obtained by the complexing agent assisted sol–gel method	269
Ni	Alumina supported NiO catalysts	AA;XPS;S	As for Al	269
Pd	Pd–HZSM-5	AA;-;L	A catalyst with a palladium loading of 0.53 wt.% exhibited good isomerization performance, which was further improved by severe acid treatment. A total conversion of 35.3 mol% and a high selectivity of 78%	270
Pt	Pt–activated carbon	XPS;SIMS;S	Pt–activated (0.3 wt.%) carbon catalysts were prepared by the incipient wetness method, followed by H2 reduction at 300 °C for 2 h. Pt catalysts with thermally-treated activated carbon had lower ignition temperatures	271
Pt	Pt–Sn/MgO	AA;ETA;L	Microwave digestion allowed recovery of metal of 100% for all the catalysts analysed and exhibited significantly better precision values than other digestion methods	272
Ru	Titania, zirconia and supported Ru	AE;ICP;L	Wet air oxidation of acidic and alkaline Kraft bleaching plant effluents (total organic carbon (TOC) content 665 and 1380 mg 1^−1, respectively) was investigated in a batch slurry reactor in the presence of titanium or zirconium oxides, or ruthenium catalysts. No leaching of Ru, Ti or Zr was detected. DLs of 0.2, 0.1 and 0.1 mg 1^−1 were obtained, respectively	273
Ti	Dehydrogenation catalyst	AE;ICP;L	Sulfation of the catalyst increased the acidity of the Lewis acid sites, which in turn resulted in a further increase of the catalytic activity. The maximum conversion obtained was 17%	274
Ti	Titania, zirconia and supported Ru	AE;ICP;L	As for Ru	273
V	Dehydrogenation catalyst	AE;ICP;L	As for Ti	274
Various	Exhaust gas catalyst, Pd–Ce–alumina	XPS;XRF;S	Hydrothermally aged (1000/850 °C, 12/16 h) Pd–Ce–supported alumina catalysts with high and low Ce content were prepared and tested in conversion of gas mixtures. The catalysts were characterised by H2-adsorption, XPS, FTIR, SO2–NO–O2–TPD, XRD, XRF and N2-physisorption	275
Various	Ammonia catalyst precursor	AE;ICP;L	No details given	276
Various	Hydrotalcites	AA;ETA;L	No details given	277
Zr	Titania, zirconia and supported Ru	AE;ICP;L	As for Ru	273

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Several reports on developments of the determination of various components of cement have been published this review year. The analysis of sulfur trioxide by ICP-AES has been reported.²³¹ Sample (0.5 g) was decomposed by boiling with 35 ml of H₂O and 10 ml of HCl (50%) and filtered. The digest was diluted to 200 ml before analysis. Plasma conditions included the use of the 282.037 nm line with an incident power of 650 W. The detection limit was 77 ng ml⁻¹ at the instrument. Calibration was achieved by standard additions with recoveries between 100–103% and typical RSDs of 0.45%. The results compared well with those obtained by traditional gravimetric analysis. A bench-top energy-dispersive X-ray fluorescence instrument equipped with a low-power X-ray tube and a gas-filled proportional counter has been used to determine CaO, SiO₂, SiO₃, Al₂O₃ and Fe₂O₃ in cement.²³² Spectrum evaluation and quantitative analysis were performed using partial least-squares (PLS) regression. A mean relative error of 5% or better was achieved for all constituents measured. It was demonstrated how the PLS method used both explicit (characteristic peaks of the analytes of interest) and non-explicit information (correlation between concentrations of different species) to build the regression model. More valuable, the authors also demonstrated how the PLS approach was able to combine data originating from spectra that were recorded under different experimental conditions. Typically for this section another report on the analysis of cement by slurry atomisation using ICP-AES has been published.²³³ The report covers work on the complete analysis of cement for major (Ca, Si, Mg, Al and Fe) and minor (S, K, Ti, Na, P, Mn and Sr) trace elements. Calibration was achieved by using a mixture of slurried standards reference materials or aqueous standards. Measurements were made on a simultaneous ICP-AES using both axial and radial viewing. The method gave good results for certified reference materials and compared well with traditional X-ray fluorescence data. The authors claim that the method is an elegant and effective alternative to XRF after taking into consideration its cost effectiveness and simplicity.

The analysis of B in ceramic materials seems to have attracted a few publications this year. Secondary ion mass spectrometry (SIMS) has been used for the study of Zr and Ti based borides.²³⁴ For Zr-based samples (ZrB₂) SIMS measurements showed evidence for induced effects by the presence of Ni with regard to oxygen and hydrogen absorption and zirconia formation. In the case of a TiB₂Ni–B₄C/Cu joint, the ceramic–metal interface region was analysed and the extent of the Cu diffusion into the ceramic materials was established. The SIMS results were in agreement of previously published SEM-EDS data. A WD-XRF method for thedetermination of B in ceramic materials has been reported.²³⁵ A variety of materials (ceramic materials, boracic raw materials and ceramic frits) were tested using the new method and a reference method consisting of the potentiometric titration of mannitol–boric acid complex. The samples were prepared as pellets or glass discs. Different binders were studied such as mannitol and cellulose for the raw materials and polyvinylpyrrolidone and methylcellulose for the ceramic frits. Lithium tetraborate and a barium–lead glass were used to melt, dilute and homogenise the samples. The results obtained with both techniques showed relative errors from 0.7 to 3.2% for B₂O₃ content ranging between 40.8–6.3%, respectively. The diffusion of B in SiC has been studied using SIMS.²³⁶ The diffusion of implanted B in nitrogen-doped 4H- and aluminium-doped 6H-SiC were studied at temperatures between 1700 and 1800 °C. The authors found that transient enhanced B diffusion caused by implantation damage was effectively suppressed by annealing of the B-implanted samples at 900 °C prior to the diffusion anneal. The SIMS technique accurately described the concentration profiles of the B on the basis of the kick-out mechanism. This is claimed to provide strong evidence that Si self-interstitial mainly mediates B diffusion. In an separate study,²³⁷ workers found that by studying the redistribution of implanted box-shaped and Pearson B profiles in 6H-SiC by SIMS the enhanced diffusion of B can strongly be suppressed by the presence of surplus carbon.

Continuing the theme of the analysis of SiC, a series of reports have been received on the characterisation of 4H-SiC materials. The electrical characteristics and surface morphology for As ion-implanted 4H-SiC at high temperature has been published.²³⁸ High temperature ion-implantation of As⁺ into 4H-SiC substrates with a high dose of 7 × 10¹⁵ cm⁻² has been investigated as an effective technique of n-type dopant for SiC power electron devices fabrication. AFM and SIMS results revealed that the surface roughness of implanted SiC increases with the increasing of post-annealing temperature. This result suggests that the evaporation of Si atoms and As⁺ dopants from SiC surfaces decreases the thickness of As⁺ implanted layer. The electrical and structural properties of Al and B implanted 4H-SiC by SIMS and low temperature photoluminescence has been reported.²³⁹ A strong diffusion was observed for implanted B sampled towards both the inside and the surface by post-annealing at 1700 °C but not for Al implanted samples. For Al-implantation, a temperature of 1550 °C was enough for electrical activation of the receptors from the results of Hall effect measurements. From further work on positron lifetimes for both Al and B implanted samples it was proposed that a type of di-interstitial or di-vacancy mechanism is dominant for post-annealed samples. Further work on secondary defects^240,241 reports that these secondary defects in high energy implanted 4H-SiC are extrinsic dislocation loops and the distribution of them is closely related to that of excess Si and C interstitials formed by the implantation process.

As usual, a large number of papers have been published on the use of atomic spectrometry for the analysis of important archaeological artefacts. XRF has been used for the analysis of ancient pottery²⁴² and porcelain,²⁴³ EDXRF for the analysis of Chinese porcelains^244,245 and South American ceramics,²⁴⁶ and ICP-AES for the analysis of Roman pottery.²⁴⁷

3.5. Catalysts

It is no surprise that surface analysis techniques again dominate this review. Techniques include time-of-flight-secondary ion mass spectrometry (TOF-SIMS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Titania supported Nb catalysts were characterized by TOF-SIMS.²⁴⁸ Eight catalysts with different Nb loadings were prepared. Monomeric, dimeric and trimeric Nb_xO_y clusters were observed in the mass spectrum at all loadings. The tetrameric cluster was only detected at >2.8% m/m. This data suggested that polymeric species were present at loadings significantly lower than that corresponding to monolayer coverage whilst bulk phase Nb₂O₅ was present for catalysts with >60% theoretical coverage.

Fuel cell catalysts, produced by pyrolysis of mixtures of perylene tetracarboxylic dianhydride with Fe and N precursors were also studied using TOF-SIMS.²⁴⁹ To obtain a range of catalytic activities, either the heat treatment or the Fe content was varied. The precursors were Fe^II acetate and Fe^III porphyrin. The relative sensitivities of the secondary ions were mapped against the catalytic activity. Only one ion, FeN₂C₄⁺, showed a strong correlation with catalytic activity. It was proposed that this ion was derived from a 1,10 phenanthrolinic type structure at the catalytic site. The reaction and poisoning mechanisms of a LaCoO₃/Al₂O₃ model system by SO₂ was investigated by AES and XPS.^250,251 The loss of catalytic activity was assigned to surface sulfate formation, diffusion of SO₂ into the bulk and reaction to form a variety of oxysulfur species resulting in loss of the perovskite structure.

Alternatives to fire assay techniques were proposed for the determination of platinum group metals (PGE) in automobile catalysts.²⁵² Three methods were studied, i.e., an open beaker digestion method, a closed vessel microwave digestion and fusion with sodium peroxide. The resultant solutions were analysed by ICP-MS. All methods resulted in quantitative recovery of Pt and Pd but were less successful for Rh. Fusion, with sodium peroxide, was the only method that resulted in quantitative recovery of Pt, Pd and Rh through the procedure.

4 References

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