Lachat Method: Cyanide 10-204-00-2-C
Using in-line cyanide distillation, a liquid sample is first mixed with phosphoric acid, heated to 135°C, and then UV irradiated to break down metal-CN- complexes. The HCN(g) from the sample matrix passes through a Teflon membrane and is trapped into a sodium hydroxide solution. The CN- is determined colorimetrically (pyridine-barbituric acid chemistry) at 570 nm. Both standards and samples are distilled in-line. The distillation and gas diffusion steps are similar to those described in ISO method, DIN EN ISO 14403 Water Quality Determination of total cyanide and free cyanide by flow analysis.
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