Speciation of Cr(III) and Cr(VI) in environmental samples after solid phase extraction on amberlite XAD-2000

Abstract

A method for speciation of Cr(III) and Cr(VI) in real samples has been developed. Cr(VI) has been separated from Cr(III) and preconcentrated as its pyrrolidinedithiocarbamate (APDC) complex by using a column containing Amberlite XAD-2000 resin and determined by FAAS. Total chromium has also been determined by FAAS after conversion of Cr(III) to Cr(VI) by oxidation with KMnO 4. Cr(III) has been calculated by subtracting Cr(VI) from the total. The effect of pH, flow-rate, adsorption and batch capacity and effect of various metal cations and salt anions on the sorption onto the resin were investigated. The adsorption is quantitative in the pH range of 1.5-2.5, and Cr(VI) ion was desorbed by using H2SO4 in acetone. The recovery of Cr(VI) was 97 ± 4 at a 95% confidence level. The highest preconcentration factor was 80 for a 200 mL sample volume. The adsorption and batch capacity of sorbent were 7.4 and 8.0 mg g-1 Cr(VI), respectively, and loading half time was 5.0 min. The detection limit of Cr(VI) is 0.6 µg/L. The procedure has been applied to the determination and speciation of chromium in stream water, tap water, mineral spring water and spring water. Also, the proposed method was applied to total chromium preconcentration in microwave digested moss and rock samples with satisfactory results. The developed method was validated with CRM-TMDW-500 (Certified Reference Material Trace Metals in Drinking Water) and BCR-CRM 144R s (Certified Reference Material Sewage Sludge, Domestic Origin) and the results obtained were in good agreement with the certified values. The relative standard deviations were below 6%.