SOLID PHASE EXTRACTION FOR THE SPECIATION AND PRECONCENTRATION OF Cr (III) AND Cr (VI) IN WATER SAMPLE

A sensitive and selective method for the preconcentration and speciation of sub μg L −1 levels of chromium species in aqueous solutions. The agarose-based chelating adsorbents with, respectively, iminodiacetic acid (IDA) and an Poly styrene Crosslinked - DVB anion exchanger (Purolite C100), were studied for the separation and preconcentration of Cr(III) and Cr(VI) species in water. Column recoveries of all the adsorbents were plotted against pH, and it was found that at pH 3.0 the IDA adsorbent selectively adsorbs Cr(III), with a 100 ± 1.0% recovery. The Purolite C100 accumulated only Cr(VI) at this pH, again with a recovery of 99.8 ± 1.2%. A dual column system was accordingly designed, using the two adsorbents in tandem, for the separation and preconcentration of the chromium species. The effects of pH, sample flow rate, column length, eluent type, eluent volume, acid concentration and interfering ions on the recoveries of Cr (III) and Cr (VI) were carefully studied. It was shown that by passing test solutions, at pH 3.0; through the dual column system, the two chromium species could be individually collected on the columns, respectively, and eluted, one after the other. A portion of 2 mol L −1 hydrochloric acid was used for elution of each column before final measurement by flame AAS method. A preconcentration factor of 12, a detection limit of 7.7 ± 0.1μg L −1 and a precision expressed as relative standard deviation of 0.4% (at 0.3 mg L −1 ) were achieved for six replicates. Application of the developed method to the determination of chromium species in spiked river and tap water and wastewater samples, from a dye production plant, resulted in excellent agreements with accepted concentrations.