Thiolated eggshell membranes sorb and speciate inorganic selenium

Abstract

Eggshell membranes (ESMs) provide a unique, disulfide bond-rich surface. Thioglycolate reduction was used to generate thiol (–SH) groups on the ESM surface by S–S bond cleavage. The thiol-bearing ESMs (TESMs) were characterized by scanning electron microscopy and Raman spectroscopy. The fibrous network structure of the ESM is retained in the TESMs. TESMs adsorb both Se(IV) and Se(VI) but by different mechanisms: Se(VI) is retained reversibly, possibly via ionic interactions, while Se(IV) is reduced to Se(0) and deposited. We thus demonstrate speciation of selenium species, by using samples (a) as such and after prior oxidation to Se(VI), (b) preconcentration on a TESM microcolumn, (c) elution by 0.5 M HNO₃ that only elutes Se(VI) and (d) detection by graphite furnace atomic absorption spectrometry (GFAAS). The Se(IV) amount is determined by difference. For a 1.0 mL sample, the enrichment factor was 17.2, the S/N = 3 detection limit was 0.06 μg L⁻¹ and the precision was 3.3% at 0.50 μg L⁻¹. The linear range was 0.25–2.50 μg L⁻¹. The procedure was validated by analyzing selenium in certified reference materials of human hair (GBW 09101) and rice (GBW 10010). We further demonstrate utility by speciation of inorganic selenium in a series of water samples.