C18 bonded silica membrane disk modified with Cyanex 302 for Cr(III) and Cr(VI) speciation and flame atomic absorption spectrometric determination.

A new SPE method for speciation of Cr(III) and Cr(VI) has been developed using a Cyanex 302-impregnated C18 bonded silica membrane disk followed by flame atomic absorption spectrometric determination. The influence of various parameters, such as pH, flow rate, volume of sample solution, amount of Cyanex 302, and eluent type, concentration, and flow rate, on Cr(III) retention, were systematically studied. Cr(III) was quantitatively recovered from the modified sorbent at pH 4.5, while the recovery of Cr(VI) was negligible (0.5 +/- 0.5 microg) throughout the pH range studied for its sorption, thus facilitating their separation and speciation. Most of the elements associated with Cr(III) did not show strong interference during its sorption. The sorption capacity of modified disk for Cr(III) was 117.6 +/- 0.8 microg, and its enrichment factor for Cr(III) was 37. The LOD and LOQ of the method for Cr(III) were 0.88 and 2.93 microg/L, respectively. The efficiency of the disk for Cr(III) recovery remained unchanged up to 24 cycles. A certified reference material (BCR-701) was analyzed to validate the accuracy of method developed for Cr(III). The method was applied to the determination of Cr(III) and Cr(VI) species in tap water and an industrial effluent sample, with RSD < or = 1.0%.