Determination of Trace Hexavalent Chromium in Water by Digital Image Colorimetry after Homogeneous Liquid-Liquid Extraction

A method for the determination of trace hexavalent chromium in water by digital image colorimetry after homogeneous liquid-liquid extraction was proposed. 2.5 mL of the water sample was taken, then 0.125 mL of sodium dodecyl sulfate solution (20 g·L^-1), 0.3 mL of sulfuric acid solution (0.5 mol·L^-1) and 0.125 mL of acetone solution containing 0.04 mol·L^-1 diphenylcar-bozide were added in sequence, and shaken well, reacted for 5 min. A mixture of 60 μL of dimethyl phthalate and 400 μL of isopropyl alcohol was used for extraction. After vortex and centrifugation, the green (G) value of the extraction layer was read by the Color Grab software in the color colorimetric device of smart phone. It was shown that linear range of the standard curve of hexavalent chromium was 4-60 μg·L^-1, with detection limit (3s/k) of 1 μg·L^-1. Test for recovery was made on the actual water samples by standard addition method, and the determined values of hexavalent chromium obtained by this method was basically consistent with those of the national standard method GB 7467-1987, with values of the recovery in the range of 87.8%-109%, RSDs (n=6) of the determined values in the range of 2.4%-3.7%.