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 (PO(4)-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 0.1M 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 microg Pl(-1) and sample throughput of 70 samples h(-1) were achieved. The relative standard deviations for 50 and 500 microg Pl(-1) orthophosphate standards were 5.2 and 5.9%, respectively. By incorporating an ion exchange preconcentration column, a detection limit of 0.18 microg Pl(-1) was obtained for a 2-min preconcentration time (R.S.D.s for 0.1 and 1 microg Pl(-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.

Cost-effective flow injection spectrophotometric assay of iron content in pharmaceutical preparations using salicylate reagent.

A new flow injection procedure for an assay of Fe(III) by using salicylate obtained from antipyretic powder, which is a cheap and easily available reagent, is proposed. A red complex was continuously monitored by a laboratory-made green LED colorimeter. A linear calibration was obtained in the range of 1-20mgFel(-1) with a detection limit of 0.5mgFel(-1) and R.S.D.s of 1.4-5.4% (n=3, for 1-20mgFel(-1)). The new procedure was applied to assay iron contents in pharmaceutical preparations. The results were in good agreement with those of the USP standard method.

Stopped-flow injection simultaneous determination of phosphate and silicate using molybdenum blue.

Kinetic information for the phosphate-molybdate-ascorbic acid reaction can be obtained by making use of a very simple manually operated stopped-flow injection (FI) system. Various parameters (concentrations of reagents, flow rate, mixing coils, and volume of flow cell) were investigated for determination of phosphate. A stopped-FI system should be arranged for low degree of mixing (of reactants) and low dispersion so that good signals of rate changes will be observed. Simultaneous determination of phosphate and silicate by the stopped-FI technique is proposed, using a laboratory-made semi-automatic stopped-FI Analyzer with LED-based photometer. It is based on kinetic separation of phosphate and silicate using molybdenum blue. The proposed procedure has been demonstrated for the application to water samples. The results obtained agree with that of a standard method.