Flow-injection spectrophotometric determination of silicate,phosphate and arsenate with on-line column separation

The simultaneous determination of silicate, phosphate and arsenate by using flow-injection analysis with on-line column separation is described. Determinations are based on measurement of the absorbance at 810 nm of the heteropoly blue formed with ascorbic acid as reducing reagent. Effects of flow rates, temperature of reaction coils and sample injection volumes are reported; optimum conditions are 0.25 ml min^?1 for the ascorbic acid stream, 95°C for the reaction coils and 300 μl for the injection volume. With the anion-exchange column (TSK-gel SAX), the optimal flow rate of the eluent is 0.75 ml min^?1. Relative retention times depend on the concentration of the KCl/NH₃/EDTA eluting solution; separation and simultaneous determination of the three ions are satisfactory at around 10^?4 mol l^?1 concentrations of the three ions.