Hydrogen cyanide is detected by oxidation of the atmospheric sample with chloramine-T (sodium N-chloro-4-methylbenzenesulphonamide) impregnated on XAD-7 resin beads to yield cyanogen chloride. This reacts with 4-picoline (4-methylpyridine) and barbituric acid (pyrimidinetrione) also impregnated on XAD-7 beads, to yield a colour change with a maximum absorbance change around 530–565 nm. Using a modulated monochromated white light source and lock-in detector, the reagent system was able to detect HCN in air at 1 μl l−1 within 1 min.
A flow- rate through the reagent cell of 60 ml min−1 air was chosen to give the best overall performance. Lifetime tests indicated a loss of 4-picoline due to evaporation, although reagent beads through which air was drawn at 100 ml min−1 for 66 h were still able to detect 10 μl l−1 HCN in less than 1 min. The method is not reversible and could not be used to monitor HCN concentration in air, but is nonetheless useful for the detection of HCN below its toxic level in a short time.
Bentley, A.E. and Alder, J.F., 1989. Optical fibre sensor for detection of hydrogen cyanide in air: Part 1. Reagent characterization and impregnated bead detector performance. Analytica chimica acta, 222(1), pp.63-73.
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Categories: Photonics & Optoelectronics