The spectrophotometric determination of cyanide ion with isonicotinic acid-pyrazolone.

Abstract

The pyridine-pyrazolone method for the determination of cyanide ion has been used widely as Testing Method for Industrial Waste Water (JIS K 0102) and Testing Method for Supplying Water, etc., because of the selectivity and high sensitivity. But, as the pyridine-pyrazolone reagent has an unpleasant odor owing to pyridine and the reagent solution is unstable and its preparation is time-consuming, pyridine-pyrazolone method is unsuitable for routine work.
For establishing a simpler analytical procedure without using pyridine, a spectrophotometric method using isonicotinic acid and pyrazolone has been developed and the optimum conditions have been established. This reagent has no unpleasant odor and is stable in N, N-dimethylformamide-water solution. A colored product with cyanide ion has an absorption maximum at 638 nm. The calibration curve followed the Beer's law in the range of 02.5 ppm CN^- in samples.
To 1 ml of sample containing 0.052.5 ppm CN^- 2 ml of 0.05 M phosphate buffer solution (pH 6.8) and 0.1 ml of 1% chloramine T solution were added. The mixture was allowed to stand at 1525°C for 5 min. Three ml of isonicotinic acid-pyrazolone reagent was added, and the mixture was kept at 40°C±2°C for 30 min. The amount of CN- was determined from the absorbance at 638 nm.
The presence of 1000 ppm of NH₄⁺, CNO-, hydroquinone did not interfere, but the presence of 10 ppm of Cu²⁺, Zn²⁺, or Ni²⁺interfered. Thiocyanate ion gave a color similar to that of the cyanide compound.