Development of a simple and fast voltammetric procedure for determination of trace quantity of Se(IV) in natural lake and river water samples

Abstract

A simple and fast cathodic stripping voltammetric procedure for determination of trace quantity of Se(IV) in natural samples containing high concentrations of surfactants and humic substances was developed. The procedure exploiting selenium accumulation (from sample solution spiked with 0.1 mol L −1 HClO 4 and 4 × 10 −4 mol L −1 Cu(NO 3) 2) as Cu 2Se was employed as the initial method. The deposited Cu 2Se was stripped by differential pulse cathodic potential scan. The interference from dissolved organic matter such as surfactants and humic substances was eliminated by adding Amberlite XAD-7 resin to the voltammetric cell. The whole procedure was applied to a single cell, which allows one to monitor the voltammetric scan. Optimum conditions for removing the surfactants and humic substances due to their adsorption on XAD-7 resin were evaluated. The method was tested on synthetic samples spiked with surfactants and humic substances. The calibration graph for Se(IV) under optimized conditions following the accumulation of 30 s was linear in the range from 2 × 10 −9 to 2 × 10 −7 mol L −1 and was found to obey the equation y = 0.74 x − 0.61, where y and x are the peak current (nA) and Se(IV) concentration (nmol L −1), respectively. The linear correlation coefficient was r = 0.9993. The relative standard deviation for determination of Se(IV) at the concentration of 1 × 10 −8 mol L −1 was 3.7% ( n = 5). The detection limit estimated from three times the standard deviation for low Se(IV) concentration and accumulation time of 30 s was about 7.8 × 10 −10 mol L −1. The presented procedure was successfully applied to selenium determination in TMRAIN-95 certified reference material and to real samples including spiked lake and river waters for selenium speciation.