Effect Elimination of Turbidity on Diphenylcarbazide Spectrophotometric Measurement of Cr(Ⅵ) in Waste Waters

Triplex-wavelength spectrophotometric methods using diphenylcarbazide as a chromogenic reagent was established to eliminate the interference of turbidity for determining Cr(Ⅵ) in waste water. However, this method could not be used to eliminate the effect of other factors on Cr(Ⅵ) except for turbidity. In the triplex-wavelength spectrophotometric method, the measuring wavelength was 540 nm, and the reference wavelengths were 460 nm and 660 nm. The triplex-wavelength spectrophotometric method had a good correlation coefficient (r=0.9998) and precision (RSD 1.44%, for seven 8.0 μg/L standard samples). The detection limit (L_D =3.143s) was 0.3 μg/L. The average value of recoveries in waste water samples were in the range of 84.8%-93.8% using an internal standard. Compared with the single-wavelength spectrophotometric method, the triplex-wavelength spectrophotometric method had better precision and accuracy. Furthermore, the triplex-wavelength spectrophotometric method had better precision and less workload than the turbidity compensation spectrophotometric method. This method is suitable for the determination of Cr(Ⅵ) in low turbidity waste water when the absorbency is lower than 0.1000 at 540 nm. High turbidity waste water needs to be diluted before spectrophotometric measurements can be made.