Catalytic Kinetic Fluorophotometric Determination of Chromium(Ⅵ)

Based on the catalytic action of Cr(Ⅵ) on the redox reaction between H2O2 and indigo carmine, the feasibility to develop a method for fluorophotometric determination of Cr(Ⅵ) on the basis of this catalytic reaction was studied. It was found that when in a solution of total volume of 10 mL, 1.5 mL of 1.0×10-3mol·L-1 indigo carmine solution, 0.1 mL of 30% (w) H2O2 solution and 3 mL of HOAc-NaOAc buffer solution of pH 4.0 were added in succession, and the mixture was heated at 65 ℃ for 11 min, and cooled rapidly to room temperature. When in the presence of Cr(Ⅵ), significant enhancement of fluorescence was observed as measured at λem of 415 nm with λex at 330 nm, and linear relationship between values of ΔF(F-F0) and mass concentration of Cr(Ⅵ) was found in the range of 0.001-0.06 mg·L-1, with detection limit (3s/k) of 0.004 4 mg·L-1. Test for recovery was made with capsule sample as matrixes by standard addition method, value of average recovery found was 98.0%.