Simultaneous determination of orthophosphate and arsenate based on multi-way spectroscopic-kinetic data evaluation

Comparison has been made of various multivariate calibration models for the simultaneous determination of phosphate and arsenate. Both ions react with molybdate and ascorbic acid forming a blue complex. Differences appear for the two ions both with respect to spectral and kinetic behaviour. Multiway partial least squares (PLS) models based on the combined effect of spectral and kinetic differences are superior to PLS models based on either difference alone. The concentration working range was 0-88 mu mol l(-1) for phosphate and 0-27 mu mol l(-1) for arsenate. The root mean square error of prediction values were typically 6 (P) and 2 (As) mu mol l(-1) when calibration models utilising 31 spectra for each solution were applied. The spectral range was 410-820 nm, one absorbance value was measured every second nm (205 data points), and one scan/min was performed. Phosphate catalyses the reaction between arsenate and the added reagents due to the formation of one or more mixed complexes. (C) 1997 Elsevier Science B.V.