Phosphate Determination in Aqueous Samples by Complex Formation with Rhodamine B

Abstract

In this study novel approaches for determining trace levels of phosphate in aqueous pore water solutions are described. Phosphate in aqueous samples (freshwater, drinking water, soil pore water) forms an aggregate compound with molybdate and Rhodamine B in 1M HCl. Incident light directed at the Rhodamine B molybdo-phosphate aggregate follows a second order light scattering behaviour. A bench top fluorescence spectrophotometer was used for examining the light scattering properties of the aggregate as well as for examining the feasibility of using this species for quantitative analysis. In this study this approach was adapted for quantitative analysis using capillary electrophoresis equipped with laser induced fluorescence. Quantifying phosphate with CE-LIF could be achieved by detecting the Rhodamine B phosphomolybdate aggregate directly in aqueous samples. Capillary electrophoresis was also used to indirectly detect phosphate by detecting Rhodamine B that dissociated from the aggregate species prior to electrokinetic injection.