Abstract: The trace Cr(Ⅵ) is usually determined by colorimetry using diphenylcarbazine, which is not able to be dissolved in water. In this paper, the diphenylcarbazine citrate was synthesized and the solubility of the diphenylcarbazine citrate was improved notably. Therefore, a new rapid spectrometry for Cr(Ⅵ) determination in situ was established using the reagent newly synthesized and the portable photometer made in our lab. In the weak acid medium, diphenylcarbazine citrate is colored by Cr(Ⅵ) to form a magenta-colored complex as the diphenylcarbazine usually does. The molar absorptivity for Cr(Ⅵ) is 3.32×10⁴ L·mol^-1·cm^-1 at 540 nm, and the Beer's law is obeyed in the range of 0.03-2.00 mg/L. All the analysis can be completed within 3 minutes. Contents of Cr(Ⅵ) in electroplating waste water and industrial waste water were determined in situ, and all the results were satisfactory.

Key words: In situ spectrometry, Portable photometer, Cr(Ⅵ), Diphenylcarbazine citrate