ASTM D7237 Standard Test Method for Free Cyanide with Flow Injection Analysis (FIA) Utilizing Gas Diffusion Separation and Amperometric Detection
This is a new standard test method that was developed by ASTM Committee D19 to determine the concentration of free cyanide in an aqueous wastewater or effluents. The method detects free cyanide (HCN and CN-) and a few weak metal-cyanide complexes (Zn and Cd) that are easily dissociated into free cyanide ions under the conditions of the test.
The treated sample is introduced into a flow injection analysis (FIA) system where it is mildly acidified at pH 6 – 8 in an effort to measure the hydrogen cyanide (HCN) that would be present in an aqueous environment. The method does not utilize ligand exchange reagents. Hydrogen cyanide gas diffuses from the acid stream through a hydrophobic gas diffusion membrane into an alkaline acceptor stream. The diffused cyanide passes through an amperometric flow cell. In the presence of cyanide, silver in the working electrode of the flow cell is oxidized at the applied potential. The anodic current measured is directly proportional to the concentration of cyanide.