Preconcentration And Speciation Of Chromium In A Sequential Injection System Incorporating Dual Mini-columns Coupled With ETAAS

A procedure for pre-concentration and speciation of chromium was developed by employing solid-phase extraction with dual mini-columns in a sequential injection analysis system with detection by electrothermal atomic absorption spectrometry (ETAAS). At pH 5.8, the sample solution containing Cr(Ⅲ) and Cr(Ⅵ) was firstly aspirated to flow through a Chlorella vulgaris cell packed mini-column on which the Cr(Ⅲ) was retained. The effluent was afterwards directed to flow through a 717 anion exchange resin mini-column accompanied by the retention of Cr(Ⅵ). Thereafter, Cr(Ⅲ) and Cr(Ⅵ) were eluted by employing 0.04 mol/L and 1.0 mol/L nitric acid, respectively, and the eluates were quantified with detection by ETAAS. Chemical and flow variables governing the performance of the system were investigated. By using a sampling volume of 600μL, sorption efficiencies of 99.7% for Cr(Ⅲ) and 99% for Cr(VI) were achieved along with enrichment factors of 10.5 for Cr(Ⅲ) and 11.4 for Cr(Ⅵ), within linear ranges of 0.10-2.5μg/L for Cr(Ⅲ) and 0.12-2.0μg/L for Cr(VI). Detection limits of 0.02μg/L for Cr(Ⅲ) and 0.03μg/L for Cr(Ⅵ) along with RSD values of 1.9% for Cr(Ⅲ) and 2.5% for Cr(Ⅵ) (1.0μg/L, n=11) were obtained. The novelty of this method is that chromium speciation was obtained using by dual mini-columns coupled with ETAAS and the sensitivity was improved.The present procedure was validated by analyzing chromium in a certified reference material of GBW08608 and further demonstrated by spiking recoveries of chromium species in river and tap water samples and satisfactory results were obtained. The resent system provides a useful procedure for the determination of trace chromium and chromium speciation in water samples.