1988 Volume 37 Issue 2 Pages 76-82
The diphenylcarbazone method proposed by Tomonari, and Utumi et al. is very useful for the determination of low concentrations of chloride ion (01.0 mg/l). However, the reproducibility of the method is not satisfactory. We studied about the factors affecting the absorbance of Hg(II)-diphenylcarbazone complex. The process were as follows: under constant temperature (preferably less than 20 °C) and sufficient shielding from light, 2 ml of the Hg(II) reagent {1.0×10-4 M Hg(NO3)2+0.5×10-4 M HgBr2} in 1×10-2 M HNO3 solution was added to 10 ml of the sample solution with 01.0 mg/l Cl-. Ten ml of benzene was added followed by the addition of 2 ml of diphenylcarbazone reagent (0.05 g diphenylcarbazone-diphenylcarbazide equimolar mixture/100 ml EtOH). The mixture was allowed to stand for more than 15 min before shaking at constant rate (e.g. 180 times/min) for 30 s. After shaking, the mixture was again made to stand for 5 min and the organic phase was separated and the absorbance of the extracted complex {Hg(II)-diphenylcarbazone complex} was finally measured at 560 nm. By the above procedure, good reproducibility for making a calibration curve was obtained with better linearity. The relative standard deviation was 1.6% at [Cl-] =1.0 mg/l(n=6). The analytical reactions involved were also discussed.
