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| The complex bound cyanide is liberated at a pH of 3.8 by influence of UV light. For this a UVB lamp is used and a digestion spiral of borosilicate glass. UV light with a wavelength smaller than 290 nm is filtered out, thus preventing conversion of thiocyanate into cyanide. Next the hydrogen cyanide, which is freed at a pH of 3.8 and a temperature of 125 °C, is distilled over. The distillate is buffered atpH 5.2. The liberated hydrogen cyanide reacts with chloramine-T by forming cyanogen chloride. This reacts with iso-nicotinic acid and 1,3-dimethyl barbituric acid into a purple coloured complex. The extinction of the solution is measured at 600 nm, with a matrix correction at 400 nm, and is a measure for the present total quantity of cyanide, with exception of thiocyanate compounds. In order to determinethe content of free cyanide, prior to the distillation a zinc sulphate dilution is added to the sample flow. As a consequence the presentiron cyanides precipitate as zinc cyanoferrate complex, thus preventing the determination of these iron cyanides. Next the hydrogen cyanide, which is freed at a pH of 3.8 and a temperature of 125 °C, is distilled over and determined photometrically. |
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| Matrices qualified by the Dutch RvA: | Wastewater, Drinking water, Groundwater, Surface water |
| Reporting limit: | 1 μg/l, matrix dependent |
| Measurement uncertainty: | 20% |
| Sustainability: | 7 days
, if conserved with NaOH
|
| Sampling bottle: | Glass
, brown
, 100 ml
, conservation with NaOH
(fill up to the neck of the bottle)
|
