ASSAY OF SOLUBLE REACTIVE PHOSPHORUS AT NANOMOLAR LEVELS IN NONSALINE WATERS

A simple, yet precise and accurate assay for SRP in low ionic strength water is described (mean error < 0.03 nM, 99% C.I. < +/- 3 nM in the 10-100-nM range for a 25-30-fold concentration factor). The method relies on the use of chromatographic cartridges to concentrate the sample and the automated malachite green method to quantify SRP. For waters with a very low salt content, the concentration factor may be further increased by more than one order of magnitude by processing a higher volume of sample. Interferences of As5+ and Si compounds are removed during the concentration step, which is rapid and clean.