Simple Colorimetric Analysis for Determining Hexavalent Chromium with High Sensitivity via Homogeneous Liquid-Liquid Extraction

Colorimetric analysis with diphenylcarbazide has been used as a simple method to determine hexavalent chromium (Cr(VI)). However, the low sensitivity of this technique makes it difficult to determine concentrations close to the environmental standard value (0.05 mg/L). We found that the phase separation phenomenon produced a small amount of the extraction phase when a mixture of 2-propanol and a small amount of dimethyl phthalate were added to a water sample, and that the Cr(VI)-diphenylcarbazide complex was extracted into this phase with high efficiency. Based on these findings, we report a simple method for colorimetric analysis for determining Cr(VI) with high sensitivity via homogeneous liquid-liquid extraction using water, 2-propanol, and dimethyl phthalate. As a result, the extraction percentage for Cr(VI) was 88% and the concentration factor improved up to 121-fold (27.4 mL -> 226 mu L). Using the proposed extraction method, determination limit (10 sigma) and detection limit (3 sigma) were 0.11 ppb and 0.03 ppb, respectively. This method can be employed for the determination of hexavalent chromium in groundwater systems by the use of EDTA as masking agent.