Abstract
A method is described for the mutual determination of orthophosphate and arsenate by the use of a dual-wavelength spectrophotometer. It is based on the difference in the optical absorption between heteropoly blue formed from orthophosphate and that from arsenate. The difference in absorbances at 825.0 nm and 855.2 nm is proportional to the concentration of orthophosphate in the range from 1.00 × 10-6 M (1 M = 1 mol dm-3) to 9.00 × 10-6M in the presence of 2.00 × 10-5 M arsenate with less than 6% relative error. Arsenate in the presence of 2.00 × 10-5 M orthophosphate can also be determined over the range from 1.00 × 10-6 M to 9.00 × 10-6 M with less than 5% relative error. The effect of various ions on the determinations of orthophosphate and arsenate was examined.
