Advances in the determination of inorganic ions in potable waters by ion chromatography

Abstract

Ion chromatography (IC) is now a well-established methodology for the analysis of ionic species. The technique is applicable to the determination of a wide range of solutes in many sample types, although the determination of inorganic ions in potable waters continues to be the most widely used application of ion chromatography. Many standardization and regulatory bodies, such as the American Society for Testing and Materials (ASTM), International Organization for Standardization (ISO), and US Environmental Protection Agency (EPA), have approved methods of analysis based upon IC, most of which have been published within the last decade. Recent developments in the field of IC, such as the use of higher capacity columns, larger loop injections, more complex sample preparation and detection schemes, have been incorporated into these new approved methods. These advances allow the determination of environmentally significant contaminants, such as common inorganic anions, bromate, perchlorate and chromate, at trace levels in potable waters using ion chromatography.

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Peter E. Jackson

Kirk Chassaniol

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Introduction

Ion chromatography (IC) can now be considered a well-established, mature technique for the analysis of ionic species. A number of standards organizations, such as the American Society for Testing and Materials (ASTM) and International Organization for Standardization (ISO), have regulatory methods of analysis based upon IC.¹ The technique is applicable to the determination of a wide range of solutes in diverse sample matrices, although the analysis of inorganic ions in processed drinking water (plus associated ground- and surface waters) remains the single most important application of IC.² Ion chromatography has been approved for compliance monitoring of common inorganic anions in US drinking water since the mid-1980s, as described in US EPA Method 300.0. This method was first issued in 1983 for the analysis of inorganic anions, and revised in 1993 to include Part (B) for the determination of inorganic disinfection byproduct (DBP) anions.³ Other industrialized countries have similar health and environmental standards and a considerable number of regulatory IC methods have now been published worldwide for the analysis of inorganic ions in potable waters.

Recent advances in instrumentation, columns and detection technology have expanded the scope of IC beyond the analysis of the common inorganic anions to include solutes such as DBP anions, alkali and alkaline earth cations, chromate and perchlorate. There has also been considerable activity regarding new regulations and methods which use IC for potable water analysis, and a number of new US EPA and ISO methods based on IC have been published over the last decade. These new methods tend to be more complex, i.e., they use higher capacity columns, alternate detection schemes and involve more sample preparation, than those required for the determination of common anions at mg L⁻¹ levels. A list of the key regulatory IC methods used for potable water analysis is given in Table 1. This paper will review recent advances in the use of IC for the determination of common inorganic anions, DBP anions, chromate, perchlorate and common cations in potable waters.

Table 1 Key regulatory methods published for the analysis of inorganic ions in potable water using ion chromatography

Method #	Analyte(s)	Date^a	Comment
a Date of first publication, earlier methods may have since been revised.
US EPA 300.0	F^−, Cl^−, NO2^−, Br^−, NO3^−, PO4^3−, SO4^2−	1983	AS4A column and conductivity detection
ISO 10304-1	F^−, Cl^−, NO2^−, Br^−, NO3^−, PO4^3−, SO4^2−	1992	Anion-exchange column and conductivity detection
US EPA 300.0 (B), Revision 2.1	BrO3^−, ClO2^−, ClO3^−	1993	AS9-SC column and conductivity detection
ISO 10304-4	Cl^−, ClO2^−, ClO3^−	1997	Anion-exchange with conductivity, UV/VIS or amperometric detection
US EPA 300.1 (B)	BrO3^−, Br^−, ClO2^−, ClO3^−	1997	AS9-HC column and conductivity detection
ASTM D 6581 - 00	BrO3^−, Br^−, ClO2^−, ClO3^−	2000	AS9-HC column and conductivity detection
US EPA 317.0	BrO3^−, Br^−, ClO2^−, ClO3^−	2000	AS9-HC column and conductivity with post-column reaction for bromate
US EPA 321.8	BrO3^−	1997	PA-100 column and ICP-MS detection
ISO 15601	BrO3^−	2001	Anion-exchange and conductivity detection
US EPA 314.0	ClO4^−	1999	AS16 column and conductivity detection
ASTM D 2036-97	CN^−	1997	AS7 column and amperometric detection
EPA Method 218.6	Hexavalent chromium (CrO4^2−)	1991	AS7 column and post-column reaction
ISO 10304-3	CrO4^2−, I^−, SO3^2−, SCN^−, S2O3^2−	1997	Anion-exchange with conductivity, UV/VIS or amperometric detection
ISO 14911-1	Li^+, Na^+, NH4^+, K^+, Mn^2+, Ca^2+, Mg^2+, Sr^2+, Ba^2+	1998	Cation-exchange and conductivity detection

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Advances in instrumentation

Ion chromatography is essentially a liquid chromatographic technique applied specifically to the determination of ionic solutes. The instrumentation used for IC is similar to that employed for conventional high performance liquid chromatography (HPLC), although the wetted surfaces of the chromatographic system are typically made of an inert polymer, such as polytetrafluoroethylene (PTFE), or more commonly polyetheretherketone (PEEK), rather than stainless-steel. This is due to the fact that the corrosive eluents and regenerant solutions used in IC, such as hydrochloric or sulfuric acids, can contribute to corrosion of stainless-steel components.² Ion chromatography also differs from HPLC in that ion exchange is the primary separation mode and conductivity is the principle method of detection. Advances in IC instrumentation have generally kept pace with improvements in conventional HPLC systems. Typical peak area and retention time reproducibility obtained for inorganic analytes at mg L⁻¹ levels is of the order of 0.5 and 0.2% RSD, respectively.⁴ Method detection limits (MDLs) are typically in the low µg L⁻¹ range for most inorganic analytes under standard operating conditions, although they can be significantly lower depending upon the application.

Increased automation is another advance of modern IC instrumentation. In addition to increased functionality of autosamplers, which not only automatically inject samples, but can now perform dilution and automated sample preparation, devices which electrolytically generate acid or base eluents are also commercially available. Automated eluent generation has been shown to produce high purity eluents with minimal baseline shift during gradient separations and also to improve the reproducibility of gradient methods.⁵ Suppressor devices, which convert the eluent ion to its much less conductive weak acid (or weak base) form and enhance the conductance of the analyte ion pair, have evolved from packed bed columns that required frequent, off-line regeneration to continuously regenerated devices which electrolytically produce the acid or base required for suppression. These devices further increase the level of automation of IC systems, in addition to providing minimal band broadening and low background noise.⁴ In addition to conductivity, other detection methods, such as ultraviolet/visible (UV/VIS) absorption or amperometry, have proven to be highly sensitive for certain absorbing or electroactive species, while post-column derivatization followed by UV/VIS or fluorescence detection is an important approach for selected anions, transition metals, lanthanides and actinides. Also, the use of advanced detection techniques, such as mass spectrometry (MS) and inductively coupled plasma (ICP) spectrometry, coupled to IC separations continues to increase.¹

Common inorganic anion analysis

The US National Primary Drinking Water Standards specify a maximum contaminant level (MCL) for a number of common inorganic anions, including fluoride, nitrite and nitrate. The MCLs are specified to minimize potential health effects arising from the ingestion of these anions in drinking water. Consequently, the analysis of these anions in drinking waters is mandated, as are the analytical methods that can be used for their quantification.⁶ Other common anions, such as chloride and sulfate, are considered secondary contaminants. The Secondary Drinking Water Standards are guidelines regarding taste, odor, color and certain aesthetic effects that are not federally enforced. However, they are recommended to all the States as reasonable goals and many of the States adopt their own enforceable regulations governing these contaminants.⁷

Ion chromatography has been approved for compliance monitoring of these common inorganic anions in drinking water in the US since the mid-1980s, as described in EPA Method 300.0. This method specifies the use of a Dionex IonPac AS4A anion-exchange column with an eluent of 1.7 mM sodium bicarbonate/1.8 mM sodium carbonate for the separation of common anions. An optional column may be substituted provided comparable resolution of peaks is obtained and that the quality control requirements of the method can be met.³ Conductivity is used as a bulk property detector for the measurement of inorganic anions after suppression of the eluent conductance with an anion micromembrane suppressor (AMMS) operated in the chemical regeneration mode.

Fig. 1(A) shows a chromatogram of a standard containing low mg L⁻¹ levels of inorganic anions and acetate, obtained using a recently developed IonPac AS14A anion-exchange column with an anion self-regenerating suppressor (ASRS). The higher capacity AS14A column provides better overall peak resolution compared to the IonPac AS4A column originally specified in Method 300.0, complete resolution of fluoride from acetate, and improved resolution of fluoride from the void peak. All the anions of interest are well resolved within a total run time of less than 10 min. The ASRS provides similar method performance to the AMMS originally specified in Method 300.0, but with the added convenience that the regenerant solution is electrolytically generated from the conductivity cell effluent. Fig. 1(B) shows a chromatogram of a drinking water sample obtained using the IonPac AS14A column and ASRS device. The linear concentration range, coefficients of determination (r²), and calculated MDLs, which can be achieved for each of the anions using Method 300.0 with an AS14A column and ASRS suppressor, are shown in Table 2.⁴

Fig. 1 Separation of inorganic anions and acetate using a block-grafted AS14A column. Conditions: column, IonPac AS14A (3 mm id); eluent, 8.0 mM sodium carbonate/1.0 mM sodium bicarbonate; flow-rate, 0.5 mL min⁻¹; detection, ASRS-ULTRA (2 mm) operated at 50 mA in recycle mode; injection volume, 25 µL; samples, (A) anion standard; (B) Sunnyvale, CA tapwater; solutes, (A) 1 - fluoride (1 mg L⁻¹), 2 - acetate (4 mg L⁻¹), 3 - chloride (2 mg L⁻¹), 4 - nitrite (3 mg L⁻¹), 5 - bromide (5 mg L⁻¹), 6 - nitrate (5 mg L⁻¹), 7 - phosphate (8 mg L⁻¹), 8 - sulfate (6 mg L⁻¹); (B) 1 - fluoride (0.03 mg L⁻¹), 3 - chloride (31.2 mg L⁻¹), 5 - bromide (0.05 mg L⁻¹), 6 - nitrate (4.5 mg L⁻¹), 7 - phosphate (0.06 mg L⁻¹); 8 - sulfate (31.0 mg L⁻¹).

Table 2 US EPA Method 300.0 peformance obtained using an IonPac AS14A column and ASRS suppressor operated in recycle mode; 150 × 3.0 mm id column and 25 µL injection were used with a DX-600 IC

Analyte	Range/mg L^−1	Linearity (r^2)	Calculated MDL^a/µg L^−1
a The MDLs were calculated as MDL = t × s, where t = 3.14 for seven replicates, and s = standard deviation of the replicate analyses.
Fluoride	0.1–100	0.9983	3.1
Chloride	0.2–200	0.9996	5.4
Nitrite-N	0.1–100	0.9999	1.8 (5.7 as NO2)
Bromide	0.1–100	0.9979	8.9
Nitrate-N	0.1–100	0.9979	1.7 (7.7 as NO3)
Orthophosphate-P	0.1–100	0.9981	5.1 (15.6 as PO4)
Sulfate	0.2–200	0.9988	9.6

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Disinfection byproduct anion analysis

Disinfection byproduct anions, such as bromate, chlorite and chlorate, pose significant health risks, even at low µg L⁻¹ levels in drinking water. The use of chlorine dioxide as a disinfectant for drinking water produces the inorganic DBP anions, chlorite and chlorate, while the presence of chlorate has been reported in waters treated with hypochlorite.⁸ Ozonation, an increasingly prevalent disinfection technique, produces bromate as a DBP anion if the source water contains naturally occurring bromide. Bromate has been judged by both the World Health Organization and the US EPA to be a potential carcinogen. The US EPA has estimated a potential cancer risk equivalent to 1 in 10⁴ for a lifetime exposure to drinking water containing bromate at 5 µg L⁻¹.⁹

The US EPA has recently issued new rules, which require public water systems (PWS) to control previously unregulated microbes (e.g., Cryptosporidium and Giardia) and cancer-causing DBPs in finished drinking water. The Stage 1 D/DBP rule specifies MCLs for a number of disinfection byproducts, including an MCL for bromate of 10 µg L⁻¹ and an MCL for chlorite of 1000 µg L⁻¹ in finished drinking water.⁹ Similar regulatory efforts are also under development in both Europe and Japan.¹⁰ Of the methods listed in Table 1, EPA Method 300.1 is approved for the compliance monitoring of bromate, while Methods 300.0 and 300.1 are approved for the analysis of chlorite, chlorate and bromide (a precursor to the formation of bromate). The ISO Method 15601 is expected to be the approved method for bromate analysis when the European Union finalizes regulatory limits for bromate. Both EPA Methods 317.0 and 321.8 currently have no regulatory status, although it is anticipated that at least one of these methods will be promulgated for compliance monitoring when the second stage of the D/DBP Rule is published in 2002.

EPA Method 300.0 was updated in 1993 to include Part (B) for the determination of bromate and other inorganic DBPs anions using an IonPac AS9-SC column with a carbonate/bicarbonate eluent and suppressed conductivity detection.³ EPA Method 300.1 was published as an update to Method 300.0 in 1997.¹¹ This method specifies the use of a high capacity IonPac AS9-HC column and suppressed conductivity detection for the determination of bromate, bromide, chlorite and chlorate by direct injection. The improved selectivity and high capacity of the AS9-HC column permits the use of a 200 µL injection volume, which in turn provides MDLs of 1.44, 1.32, 0.98, and 2.55 µg L⁻¹ for chlorite, bromate, bromide and chlorate, respectively.¹¹ The practical quantitation limit (PQL) of Method 300.1 for bromate is approximately 5 µg L⁻¹ and the method can tolerate the presence of up to 200 mg L⁻¹ chloride without the need for sample pretreatment.¹⁰ ASTM Method 6581-00 specifies the same analytical conditions as EPA Method 300.1, but also includes precision and bias data for reagent, drinking and bottled waters obtained through an interlaboratory validation study.¹² In practice, the PQL for bromate of approximately 5 µg L⁻¹ that is obtained with Methods 300.1 and 6581-00 is much closer to the current MCL specified for bromate than is desirable. Hence, the most recently developed IC methods for the analysis of DBP anions have employed other approaches for improving the MDL for bromate.

The detection limit for bromate determined with suppressed conductivity detection can be improved further by using preconcentration after appropriate sample pretreatment. ISO Method 15601 specifies the preconcentration of a 6 mL volume of drinking water upon an appropriate anion-exchange column, after firstly reducing the total ionic strength of the sample by passing it through three cation-exchange pretreatment cartridges in the barium, silver and hydronium ion forms, respectively.¹³ This pretreatment procedure reduces the sample concentration of sulfate, chloride, and carbonate, and allows quantitative recovery of bromate in drinking waters when preconcentrating a 6 mL sample volume.

Post-column derivatization is another approach used to improve detection limits for inorganic DBP analysis. The use of UV/VIS detection with a variety of post-column reagents, including chlorpromazine, o-dianisidine, fuchsin and excess bromide (or iodide) under acidic conditions, has been shown to allow sub-µg L⁻¹ MDLs for bromate.¹⁴ The US EPA has recently developed Method 317.0, which specifies the use of an IonPac AS9-HC column and suppressed conductivity detection plus post-column addition of o-dianisidine (ODA) to enhance the visible detection of bromate.¹⁵ This method allows quantification of all the key DBP anions and bromide at low µg L⁻¹ levels using conductivity detection, while post-column addition of ODA followed by visible detection allows quantitation of bromate down to 0.5 µg L⁻¹. Fig. 2 shows the chromatograms from a direct injection of drinking water spiked with DBP anions obtained using dual (A) suppressed conductivity and (B) UV/VIS detection at 450 nm after post-column addition of ODA. The benefits of using post-column reaction (PCR) detection can clearly be seen, as bromate is resolved from chlorite on both detector channels. However a significantly enhanced response is shown on the absorbance detector after post-column reaction with ODA (B), compared to the response obtained using conductivity (A).

Fig. 2 Determination of DBP anions and bromide in spiked drinking water using dual suppressed conductivity and UV/VIS detection after post-column reaction. Conditions: column, IonPac AS9-HC (4 mm id); eluent, 9.0 mM sodium carbonate; flow-rate, 1.0 mL min⁻¹; detection, (A) suppressed conductivity with ASRS-ULTRA (4 mm) operated at 100 mA in external water mode, (B) UV/VIS at 450 nm after post-column reaction with o-dianisidine; PCR flowrate, 0.7 mL min⁻¹; PCR temperature 60 °C; injection volume, 225 µL; sample, spiked Sunnyvale, CA tap water; solutes, (A), 1 - chlorite (109 µg L⁻¹), 2 - bromate (11.9 µg L⁻¹), 3 - bromide (135 µg L⁻¹), 4 - chlorate (169 µg L⁻¹), (B) 5 - bromate (11.5 µg L⁻¹).

In addition to post-column reaction methods, electrospray tandem mass spectrometry (MS-MS) and inductively coupled plasma mass spectrometry (ICP-MS) have been used as specific detection techniques for the analysis of bromate.^16,17 US EPA Method 321.8 specifies the use of a Dionex PA-100 anion-exchange column and detection of bromate using ICP-MS. This approach can achieve an MDL for bromate of 0.3 µg L⁻¹, although the sample must first be pretreated to remove tri-substituted haloacetic acids and separation conditions must be chosen to provide complete resolution of bromate from brominated haloacetic acids, as these species can interfere with the analysis.¹⁷ The obvious disadvantage of these MS-based detection techniques is that they each add considerable complexity and significant cost to the analysis, and to date no IC method based on MS or ICP-MS detection has been promulgated for the regulatory monitoring of bromate or any other DBP anions.

Perchlorate analysis

Ammonium perchlorate, a key ingredient in solid rocket propellants, has recently been found in ground- and surface waters in a number of States in the US, including California, Nevada, Utah, Texas, New York, Maryland, Arkansas and West Virgina.¹⁸ Perchlorate poses a human health concern as it interferes with the ability of the thyroid gland to utilize iodine to produce thyroid hormones. Current data from the US EPA indicates that exposure to less than 4–18 µg L⁻¹ perchlorate provides adequate health protection. Perchlorate contamination of public drinking water wells is a serious problem in California where the Department of Health Services has adopted an action level for perchlorate of 18 µg L⁻¹.¹⁹

Perchlorate is listed on the US EPA contaminant candidate list (CCL) as a research priority under the categories of health, treatment, analytical methods and occurrence priorities.²⁰ In addition, the EPA has recently revised the unregulated contaminant monitoring rule (UCMR) and added perchlorate to List 1 for assessment monitoring.²⁰ Monitoring of List 1 contaminants has commenced at 2 774 large PWS and at a representative sample (800 out of 65 600) of small PWS, as of January 1, 2001.²⁰ The results from these systems will be used to estimate the national occurrence of the compounds on List 1 and the data will then be used to evaluate and prioritize contaminants on the CCL.

The US EPA has promulgated Method 314.0 for the analysis of perchlorate, as required by the recent changes to the UCMR. This new method is based on the use of a high capacity IonPac AS16 column, large loop injection and suppressed conductivity detection to quantify perchlorate at low µg L⁻¹ levels.²¹ The AS16 column is packed with a very hydrophilic anion-exchange resin, which allows the elution of the hydrophobic perchlorate ion with good peak shape and high chromatographic efficiency.¹⁸ The high capacity of this column allows the direct injection of a 1000 µL sample volume, which is necessary to achieve the MDL required for this application. Fig. 3(A) shows a chromatogram of a 20 µg L⁻¹ perchlorate standard obtained using the AS16 column with a 1000 µL injection loop, a 65 mM hydroxide eluent and suppressed conductivity detection. Under these conditions, perchlorate elutes within 10 min while the common inorganic anions all essentially elute at the column void volume. Method 314.0 has a calculated MDL of 0.5 µg L⁻¹, based upon the standard deviation obtained from seven replicates injections of a 2 µg L⁻¹ standard. The method is linear in the range of 2.0 to 100 µg L⁻¹ and quantitative recoveries are obtained for low µg L⁻¹ levels of perchlorate in spiked drinking- and ground water samples.²¹ A chromatogram of potable water spiked with perchlorate is shown in Fig. 3(B).

Fig. 3 Determination of perchlorate using an AS16 column. Conditions: column, IonPac AS16 (4 mm id); eluent, 65 mM potassium hydroxide; eluent source, EG40; flow-rate, 1.2 mL min⁻¹; detection, suppressed conductivity with ASRS-ULTRA (4 mm) operated at 300 mA in external water mode; injection volume, 1000 µL; sample, (A) perchlorate standard; (B) Sunnyvale, CA tap water spiked with 4.0 µg L⁻¹perchlorate; solutes (A), 1 - perchlorate (20 µg L⁻¹); (B) 1 - perchlorate (3.8 µg L⁻¹).

Hexavalent chromium analysis

Chromium (total) is a primary drinking water contaminant in the US with an MCL of 100 µg L⁻¹, while the World Health Organization recommends 50 µg L⁻¹ as a guideline.²² Hexavalent chromium is the most toxic form of the metal, in addition to being a suspected carcinogen. The California Department of Health Services has recently issued a revised public health goal (PHG) of 2.5 µg L⁻¹ for total chromium and 0.2 µg L⁻¹ for hexavalent chromium.²² Cr(VI) can be separated (as the chromate anion) on a high capacity, IonPac AS7 anion-exchange column then quantitated using a UV/VIS detector after post-column reaction with diphenylcarbohydrazide, as specified in US EPA Method 218.6.²³ Alternatively, ISO Method 10304-3 specifies an anion-exchange column and direct UV/VIS detection for the determination of chromate. While not as sensitive as the post-column reaction approach described in EPA Method 218.6, direct detection at 365 nm allows a quantitation limit of 20 µg L⁻¹ for chromate.²⁴

EPA Method 218.6 is validated for the determination of hexavalent chromium in drinking water, ground waters and industrial wastewaters. Fig. 4 shows a chromatogram of a spiked ground water sample obtained using the conditions described in Method 218.6. No interfering peaks are observed when using this very selective detection approach for Cr(VI) analysis. Average recoveries in the order of 98–105% were obtained for 100 µg L⁻¹ Cr(VI) solutions spiked into reagent, drinking- and ground waters.²³ An MDL of 0.3 µg L⁻¹ for Cr(VI) can be achieved using a 250 µL injection, which means that further modifications to Method 218.6, such as the use of a larger injection volume and longer reaction coil (to increase residence time), are required in order to meet the new California PHG of 0.2 µg L⁻¹ for hexavalent chromium.²⁵

Fig. 4 Determination of chromate in ground water using EPA Method 218.6. Conditions: column, IonPac AS7 (4 mm id); eluent, 250 mM ammonium sulfate/100 mM ammonium hydroxide; flow-rate, 1.5 mL min⁻¹; detection, UV/VIS at 530 nm after post-column reaction with 2 mM diphenylcarbazide/10% methanol/1.0 M sulfuric acid delivered at 0.5 mL min⁻¹; injection volume, 100 µL; sample, spiked ground water; solute, chromate (50 µg L⁻¹).

Inorganic cations and ammonia

The majority of the inorganic cations listed as primary drinking water contaminants in the US are transition metals, which are most commonly analyzed using spectroscopic methods, such as atomic absorption spectroscopy and inductively coupled plasma.¹ Sodium and potassium are routinely monitored in potable waters, while the levels of calcium and magnesium determine the hardness of drinking water.⁶ Ion chromatography provides a straightforward method for the simultaneous analysis of alkali and alkaline earth cations (plus ammonia) in drinking water, as described in ISO Method 14911-1.²⁶ A key benefit of this approach is the ability to determine ammonia in complex samples that contain both inorganic cations and organic amines, as the latter compounds can interfere with the conventional colorimetric or ion-selective electrode methods used for ammonia analysis.

Fig. 5(A) shows an example of a separation of alkali and alkaline earth cations and ammonia, obtained using the approach described in ISO Method 14911-1, i.e., carboxylate functionalized, cation-exchange column and suppressed conductivity detection. MDLs in the low- to sub-µg L⁻¹ range can be achieved for the common cations and ammonia using this approach. Fig. 5(B) shows the determination of these cations and ammonia in a drinking water sample.

Fig. 5 Separation of alkali and alkaline earth cations plus ammonia. Conditions: column, IonPac CS16 (5 mm id); eluent, 30 mM methanesulfonic acid; flow-rate, 1.0 mL min⁻¹; detection, suppressed conductivity with a CSRS-ULTRA (4 mm) operated at 100 mA in recycle mode; injection volume, 25 µL; samples, (A) cation standard; (B) Sunnyvale, CA tap water; solutes (A) 1 - lithium (0.1 mg L⁻¹), 2 - sodium (0.5 mg L⁻¹), 3 - ammonia (0.6 mg L⁻¹), 4 - potassium (1.2 mg L⁻¹), 5 - magnesium (0.6 mg L⁻¹), 6 - calcium (1.2 mg L⁻¹); (B) 1 - lithium (0.003 mg L⁻¹), 2 - sodium (24.7 mg) L⁻¹, 3 - ammonia (0.08 mg) L⁻¹, 4 - potassium (1.23 mg L⁻¹), 5 - magnesium (8.94 mg), L⁻¹ 6 - calcium (23.2 mg L⁻¹).

Conclusions

The determination of inorganic anions and cations in potable waters continues to be the most widely used application of ion chromatography. Many inorganic anions that have adverse human health effects, such as fluoride, nitrite, nitrate, bromate, chlorite, perchlorate and chromate, can be analyzed in potable waters using IC. Similarly, a number of other inorganic contaminants, such as chloride, sulfate, sodium, ammonium, potassium, magnesium and calcium, can also be monitored using IC. Many regulatory and standards organizations, such as the US EPA, ASTM, and ISO, have approved methods of analysis based upon IC, most of which have been published within the last 10 years. These recently developed methods tend to reflect general advances in the field of IC, such as the use of higher capacity columns, large loop injections, and more complex sample preparation and detection schemes. This, in turn, allows the determination of inorganic contaminants at lower detection limits and expands the range of analytes that can be measured in potable waters.

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