Method OIA-1677 demonstrates greater specificity for cyanide in matrices where interferences have been encountered using existing cyanide amenable to chlorination (CATC) methods. In addition, Method OIA-1677 measures cyanide at lower concentrations and offers improved precision and accuracy over currently approved CATC methods. This method offers improved laboratory safety and reduces laboratory waste compared to currently approved CATC methods and, of particular note, eliminates distillation, thereby significantly reducing the possibility of laboratory accidents.
The new method (Method OIA-1677) is divided into two parts: 1) sample pretreatment and 2) cyanide quantification via amperometric detection. In the sample pretreatment step, ligand-exchange reagents are added to a sample. Reagents displace cyanide ions (CN-) from weak and intermediate strength metallo-cyanide complexes. In the flow-injection analysis system, a 200-uL aliquot of the pretreated sample is injected into the flow injection manifold. Hydrochloric acid converts the cyanide ions to hydrogen cyanide (HCN), which diffuses through a membrane into an alkaline solution where it is converted back to cyanide ion (CN-). The amount of cyanide ion in the alkaline solution is measured amperometrically with a silver-working electrode, silver/silver chloride reference electrode, and platinum counter electrode at an applied potential of zero volts. Current generated in the cell is proportional to the concentration of cyanide in the original sample, as determined by calibration.
The latest Clean Water Act Method Update Rule from the EPA proposes the use of OI-1677 for determination of Free Cyanide. An analysis for Free Cyanide did not exist when the Rule was written. If your permit has a Free Cyanide requirement then you now can use OI-1677 to satisfy this requirement.