Comparative study of analytical methods for the determination of chromium ingroundwater samples containing iron

摘要

Determination of chromium in groundwater samples containing iron may pose analytical problems due tosorption and fixation of chromium species onto Fe(III)hydroxides.Parks et al.(Water Res. 2004, 38, 2827)hypothesized that chromium species trapped inside Fe(III) hydroxides i.e.“fixed chromium”may not besoluble by HNO3 digestion (APHA method 3030 B). In such cases, hydroxylamine digestion is required to release “fixed chromium”.To verify the hypothesis, we carried out this study on groundwater samplescontaining chromium and iron, using different methods of APHA and EPA.The results showed the presence of “fixed chromium”,ranged between 0.1 and 19.2 μg L1,contributing 0.2 to 14.1% towards true totalchromium.Digestion of samples with HNO3 released Cr(III)bound to organic complexes,but not the“fixed chromium”.The hydroxylamine digestion released“fixed chromium”,but not the Cr(III)bound to organiccomplexes.Microwave digestion of samples with HNO3+HCl was effective for the release of both“fixed”and“Cr(III)-organic complexes”.Cr(III) was only adsorbed onto suspended matter,whereas Cr(VI),and Cr(III)-organic complexes were not adsorbed onto suspended matter due to their solubility. Sample pH, buffering capacity,and matrix have a significant influence on the adsorption and fixation of chromiumspecies onto Fe(III)hydroxides.