Application of the isotope exchange method of analysis to the speciative determination of phosphorus in environmental samples

Speciative determination of phosphorus (PO43-, PO33- and total P) in natural water samples can be achieved by using the reverse isotope exchange method. Five ml of a natural water sample is taken and dil. H2SO4 solution of ammonium molybdophosphate and a definite activity (a0) of 32P (in PO43- form) are added. The solution is shaken with the 1,2-dichloroethane solution of tetraphenylarsonium molybdophosphate which contains a definite amount of P (W1). After the quickly attainable exchange equilibrium between phosphate in the aqueous phase and tetraphenylarsonium molybdophosphate in the organic phase, the activity of the organic phase (a2) is measured. The amounts of P (Wx) in the sample can be obtained by the equation of Wx=(a0/a2-1)W1. In this condition, only PO43- exchanges, while PO33- does not. Therefore, PO43- can be determined in the presence of PO33- and unexchangeable phosphorus. When the sample water is treated with Br2 water in advance, the amount of PO43- + PO33- can be obtained. When the sample is treated with H2SO4 and HNO3, then the amount of total P can be obtained. The method is compared with the conventional spectrophotometric method (the molybdenum-blue method). This method is much simpler and more rapid, and moreover, the speciative determination is possible. (author). 13 refs, 2 figs, 6 tabs