Evaluation of on-line preconcentration and flow-injection amperometry for phosphate determination in fresh and marine waters

Dissolved reactive phosphorus (DRP) was determined as orthophosphate (PO4-P) in fresh and saline water samples by flow-injection (FI) amperometry, without and with in-valve column preconcentration. Detection is based on reduction of the product formed from the reaction of DRP with acidic molybdate at a glassy carbon working electrode (GCE) at 220 mV versus the Ag/AgCl reference electrode. A 0.1 M potassium chloride solution was used as both supporting electrolyte and eluent in the preconcentration system. For the FI configuration without preconcentration, a detection limit of 3.4 mu g P l(-1) and sample throughput of 70 samples h(-1) were achieved. The relative standard deviations for 50 and 500 mu g P l(-1) orthophosphate standards were 5.2 and 5.9%, respectively. By incorporating an ion exchange preconcentration column, a detection limit of 0.18 mu g P l(-1) was obtained for a 2-min preconcentration time (R.S.D.s for 0.1 and 1 mu g P l(-1) standards were 22 and 1.0%, respectively). Potential interference from silicate, sulfide, organic phosphates and sodium chloride were investigated. Both the systems were applied to the analysis of certified reference materials and water samples. (c) 2005 Elsevier Ltd. All rights reserved.