Comparative Study of Two Different Speciation Methods for the Determination of Hexavalent Chromium in Water Samples Using Electrothermal Atomic Absorption Spectrometry

The aim of this study was to compare two different widely-used methods for the determination of hexavalent chromium (Cr(VI)) in water samples by Electrothermal Atomic Absorption Spectrometry (ETAAS). Both methods are based on the complexation - reaction of Cr(VI) with an organic complexation reagent, which is then extracted and preconcentrated in organic solvent. In the first method, ammonium pyrrolidine dithiocarbamate (APDC) is used as complexation reagent, whereas 1,5-diphenylcarbazide (DPC) is used in the second method. The speciation methods were optimized and validated. Both methods were applied for the determination of Cr(VI) in the same multi-level groundwater samples (0.060 - 42 mu g/L, n=13) and the results were compared statistically. Beside the comparison of the two extraction methods (APDC, DPC), the samples were also analyzed by Reagent Free Ion Chromatography (RFIC) with conductivity detector and statistical comparison was also performed. Paired t-test was applied and the results indicated that there was no statistically significant difference between the three methods. Useful conclusions about the analytical performance of these widely-used-in-routine-labs methods were drawn. The selectivity of Cr(VI) determination was significant for both methods. The DPC method had lower limit of detection than APDC, however the APDC method was more robust than the DPC method. Both methods are appropriate for the determination of Cr(VI) in different ground water samples at sub-mu g/L levels.