The influence of calcium and magnesium on the phosphorus monoxide molecular absorption signal in the determination of phosphorus using a continuum source absorption spectrometer and an air-acetylene flame

The determination of P by means of evaluation of PO molecular absorption bands in the air acetylene flame is an uncomplicated, reliable, and rapid analytical method, as stated by the authors in a preceding paper. However, the presence of Mg, and especially of Ca, in the sample solution causes strong suppression of the PO absorption. This is due to the formation of calcium and magnesium phosphates, which are thermally so stable that they are not decomposed in a medium temperature air - acetylene flame. Fortunately, the suppression effect can be completely eliminated by the addition of Ti to the sample, whereby titanates of Ca and Mg are formed in the flame. As these titanates are thermally more stable than the corresponding phosphates, the phosphate is released. The analytical performance of the method was verified by analyses of standard reference materials containing high concentrations of Ca. Good precision and accuracy were achieved.