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 µL). Using the proposed extraction method, determination limit (10σ) and detection limit (3σ) were 0.11 ppb and 0.03 ppb...