Isotope Dilution as a Calibration Method for Solid Sampling Electrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry

Abstract

The present paper reports on the use of isotope dilution as a method of calibration for solid sampling ETV-ICP-MS. The possibilities and limitations of this calibration strategy were evaluated by determining the Cd or Se content in solid CRMs of different origin. It was shown that since isotope ratios are only slightly affected or not affected at all by (i) matrix effects, (ii) signal drift and instrument instability and (iii) variations in the vaporization and/or transport efficiency, isotope dilution allows accurate analyses to be carried out (mean deviation between solid sampling ETV-ICP-MS results and certified values <10%). The precision attainable is determined by the sample homogeneity and is hence comparable to that obtained using other calibration techniques, such as (i) external calibration with either a solid standard or an aqueous standard solution or (ii) standard additions. An important advantage of isotope dilution over the aforementioned calibration techniques for solid sampling ETV-ICP-MS, however, is that the use of an elemental internal standard is no longer required. For some materials, accurate analytical results could not be obtained as at least one of the isotopes involved was observed to be subject to spectral interference. The use of several parameters allowing spectral interferences to be detected is discussed. Finally, solid sampling ETV-ICP-MS was used for the determination of the Cd content in tobacco as a ‘real-life’ sample and the results obtained using isotope dilution and single standard addition for calibration were compared with one another and with the result obtained (after taking the sample into solution) using pneumatic nebulization ICP-MS.