Expert multi-syringe flow-injection system for the determination and speciation analysis of iron using chelating disks in water samples

Abstract

A novel expert multi-syringe flow-injection system has been developed. This system, which is able to choose for itself the best strategy to quantify the analyte, has been applied to the spectrophotometric determination, pre-concentration and speciation analysis of iron. The determination of the lowest iron concentrations benefits from the retention of the analyte on a chelating disk (iminodiacetic acid groups) which has been placed in a laboratory-made methyl methacrylate cylindrical device. A three-way solenoid commutation valve allows the deviation of the flow towards the chelating disk to follow the pre-concentration schemes when necessary. Ammonium thiocyanate was used as the chromogenic reagent for iron(III). Total iron can be determined by on-line oxidation of iron(II) to iron(III) with a hydrogen peroxide stream. A mass calibration was feasible in the wide range from 0.019 to 3 μg. The detection limit (3 s b/ S) was 19 ng. The repeatability (RSD), calculated from 11 replicates using 3 ml injections of a 0.5 mg l −1, was 2%. When pre-concentration was not required, two linear calibration graph between 0.1 and 20 mg l −1 and between 0.2 and 35 mg l −1 for the determination of iron(III) and total iron, respectively, were obtained. The proposed technique has been validated by replicate analysis ( n=3) of a certified reference material of water with satisfactory results. The use of chelating disks offers several advantages over the conventional resin.