Specific spectrophotometric determination of hydrocyanic acid in the environment

A very simple, sensitive and specific method for the determination of hydrocyanic acid in air and water is described. Hydrocyanic acid is collected in dilute sodium hydroxide solution and then reacted at pH 7 and 100 °C with picric acid solution, forming 2,6-dinitro-5-hydroxy-4-hydroxylamino-1,3-dicyanobenzene. The absorbance of the red solution is read at 505 nm. The color system obeys Beer’s law in the range 0.1–10 mg m−3 hydrocyanic acid (0.2–20 μg g−1). The collection efficiency of the absorbing solution and the molar absorptivity (1.42 × 103 l mol−1 cm−1) were evaluated. All other important analytical parameters were studied and the method was applied to the determination of hydrocyanic acid in air samples and cigarette smoke.