EFFECT OF SAMPLE ELECTRICAL CONDUCTIVITY ON ELECTROMEMBRANE EXTRACTION OF CHROMIUM(VI)

Abstract

Electromembrane extraction (EME) of chromium(VI) ion in aqueous samples was studied for the influences of ionic contents in the samples on the extraction efficiency. Samples containing various salt concentrations (0.0-5.0 mM) represented by their electrical conductivities (1.0-630.0 µS·cm-1) were used. Preliminarily, 2-nitrophenyl octyl ether (NPOE) provided good extraction efficiency (enrichment factor) and tolerated bubble formation at high voltages and long extraction times for samples with wide range of conductivity levels owing to its viscosity and dielectric properties. The EME conditions were optimized for effective extraction of Cr(VI) using samples with high level of conductivity (5.0 mM NaCl, 630 µS·cm-1). Mixtures of NPOE with other organic solvents and ionic carriers, sample pH, types of acceptors, applied voltages and extraction times were investigated. The optimized EME conditions were that SLM was NPOE; donor was adjusted to pH 4 with 0.1 M acetate buffer; acceptor was 0.5 M acetic acid; applied voltage was 100 V; and extraction time was 15 min. The method was evaluated under the optimum conditions. The linear range of the method was 10.0-80.0 µg·L-1. The enrichment factors were approximately 80. The recoveries of 98-108% with %.R.S.D. of 1.0-2.3% were obtained. The limit of detection (LOD) and limit of quantitation (LOQ) were 2.1 and 7.2 µg·L-1, respectively. The method was applied to real water samples with variety of ionic contents, for example, drinking water, mineral water, tap water, and surface water. The matrix effect was observed. Therefore, the linearity and recovery in the real samples were evaluated using matrix-match standard method. The working ranges were about 10.0-80.0 µg·L-1. The recoveries of spiked Cr(VI) in real water samples were 93-140% with %RSD between 1.1-11.9%. The LOD and LOQ were in the range of 3.4-9.0 µg·L-1 and 12.0-24.8 µg·L-1, respectively. The method provided good extraction and preconcentration performance in variety of samples.