Multivariate calibration in inductively coupled plasma mass spectrometry. 2. Effect of changes in abundances of interfering polyatomic ions

Two multivariate calibration methods, multiple linear regression (MLR) and principal components regression (PCR), are applied to the determination of cadmium by inductively coupled plasma mass spectrometry in the presence of interfering polyatomic MoO⁺ions. The effect of changes in MoO⁺/Mo⁺ brought about by varying instrumental conditions and sample matrix content is examined. It is found that both MLR and PCR enable the accurate determination of Cd in the presence of Mo even in the presence of large variations in MoO⁺/Mo⁺; changes in MoO⁺/Mo⁺ lead to erroneous concentrations for Mo but not for Cd. The use of Th as an internal standard for correction of biased Mo concentrations arising from changes in MoO⁺/ Mo⁺ is studied; it is found that normalization of the Mo concentration based upon the measured ThO⁺/Th⁺ improves the determinations of Mo under conditions where MoO⁺/Mo⁺ varies.