Sequential injection reductive bio-sorption of Cr(vi) on the surface of egg-shell membrane and chromium speciation with detection by electrothermal atomic absorption spectrometry

Egg-shell membrane (ESM) is a unique cell surface with various functional groups, providing the potential for bio-sorption of metal species. We have demonstrated the selective retention of chromium(vi) via a reductive sorption process, while Cr(m) is virtually not retained. This includes adsorption of Cr(vi) onto the ESM surface while charge transfer on the ESM results in the reduction of Cr(vi) to Cr(m) through transient, unstable species of Cr(v) and Cr(iv). A novel procedure for chromium speciation was thus developed in a sequential injection system with detection by electrothermal atomic absorption spectrometry. The procedure includes the separation and preconcentration of Cr(vi) on ESM at pH 2 and its subsequent detection after elution, followed by conversion of Cr(m) to Cr(vi) and total chromium analysis, Cr(III) finally being obtained by subtraction. With a sampling volume of 1000 mu l, an enrichment factor of 13.3 was achieved. A linear range of 0.05-1.25 mu g I-1 for Cr(vi), along with a detection limit of 0.01 mu g 1(-1) and a precision of 3.2% at the level of 0.5 mu g l(-1) were obtained. Chromium speciation was performed by using a certified reference material of riverine water (GBW08608) and cave water.