Speciation of inorganic chromium in river water by graphite furnace-atomic absorption spectrometry after chromabond NH2 column based solid phase extraction

Chromium (Cr) can be either essential or carcinogenic depending on the chemical form. The aim of this study was to speciate Cr in water samples, collected from Blood and Mokolo Rivers, Limpopo Province. Water samples were collected from ten sampling sites from each river. The accuracy of the method was evaluated by employing standard reference material of trace elements in water (SRM 1643 f) before sample analysis. Total Cr and Cr(VI) in water samples were quantified using graphite furnace-atomic absorption spectrometry (GF-AAS). The concentrations of Cr in water samples collected from Blood and Mokolo Rivers were found in the range of 1.56 μg/L to 6.11 μg/L and 1.34 µg/L to 3.53 µg/L, respectively. A solid phase extraction (SPE) method based on chromabond NH2 column was used to determine Cr(VI) in water. In order to achieve separation of Cr(VI), the sample was pre-concentrated and passed through a conditioned chromabond NH2 column at a flow rate of 3 mL/min. Hexavalent Cr was selectively adsorbed onto the column and the contents were dried under vacuum. The retained Cr(VI) was subsequently eluted with two column volumes of 2 M HNO3 and diluted to a final volume of 10.0 mL. The limit of detection (LOD) was 0.105 µg/L and the percentage relative standard deviations were less than 10%. The validation of the procedure was performed by spiking standard solutions containing Cr(III) and Cr(VI) and the percentage recoveries were higher than 88%. The concentrations of Cr(VI) in Blood and Mokolo Rivers ranged from 0.13 µg/L to 1.99 µg/L and 0.13 µg/L to 0.55 µg/L, respectively. In Blood and Mokolo Rivers, although the concentrations of Cr(VI) are low, their values suggest a link with the industrial and agricultural activities in the area.