A nano-structured material for reliable speciation of chromium and manganese in drinking waters, surface waters and industrial wastewater effluents

摘要

A simple solid phase extraction system based on the applying the nickel-aluminum layered double hydroxide (Ni-Al LDH) as a nano-sorbent was developed for the speciation analysis of chromium and manganese by flame atomic absorption spectrometry (FAAS). The method is based on the fact that Cr(VI) and Mn(VII) oxyanions could be adsorbed on the Ni-Al(NO _3 ~-) LDH and/or exchanged with LDH interlayer NO _3 ~- ions at pH 6.0, whereas Cr(III) and Mn(II) cations pass through the LDH-packed column without retention. The determinations of total Cr and Mn, and hence indirectly Cr(III) and Mn(II), involve the pre-oxidations of Cr(III) and Mn(II) to Cr(VI) and Mn(VII) with H _2O _2 and acidic solution of KIO _4, respectively. Several important factors affecting the retention efficiency were investigated and optimized. In the optimum experimental conditions, the limits of detection (3S _b/m) for Cr(VI) and Mn(VII) were 0.51 and 0.47 ng mL ~(-1), and the relative standard deviations were 2.5 and 3.2% (C = 30.0 ng mL ~(-1), n = 6), respectively. The presented method was validated by the analysis of a certified reference material, and applied to the speciation of Cr and Mn in drinking waters, surface waters and industrial wastewater effluents.