Determination of cyanide in microliter samples by capillary electrophoresis and in-capillary enzymatic reaction with rhodanese

This paper describes a method for the determination of cyanide using in-capillary enzymatic reaction with rhodanese. Poorly absorbing cyanide is in rhodanese reaction transformed into highly absorbing thiocyanate that is further separated by capillary electrophoresis (CE) and determined spectrophotometrically at 200 nm. Cyanide is thus estimated indirectly from the result of thiocyanate quantification and moreover, it can be easily determined with sufficient sensitivity by means of CE apparatus equipped with common UV detector. The linear detection range for concentration versus peak area for the assay is from 15 to 500 μM (correlation coefficient 0.997) with a detection limit of 3 μM and a limit of quantitation 9 μM. The inter-day reproducibility of the peak area was below 3.2% and the inter-day reproducibility of the migration time below 0.1%. The method is relatively rapid, simple and can be easily automated. Moreover, only limited amount of the sample is required.