Method of standard additions for arsenic measurements in water by ICP sector field mass spectrometry at accuracy comparable to isotope dilution

Abstract

Mathematical model of the method of additions was reviewed to exclude the dilution and mass irreproducibility effects and assure the linear calibration. Selenium was identified as a high quality internal standard for arsenic measurements. At increased ratio measurement accuracy instrumental effects are important, and capabilities of the instrument must be carefully tested and accounted for. In measurements with double focusing electric and magnetic fields mass spectrometer Element 2 at medium mass resolution need for full integration of the peaks and role of the low frequency noise was evident. Averaging of the final results provided better accuracy of determination in comparison to the mean values of the intermediate data. If suitable internal standards can be selected, the method of standard additions is found to provide measurement accuracy comparable to that of isotope dilution. Comparison of the analytical signal of the test sample from direct measurements and the calibration graph is recommended as a test of the level of compensation for the possible matrix effects.