Determination of blood cyanide by headspace gas chromatography with nitrogen-phosphorus detection and using a megabore capillary column

Abstract

A method for the determination of cyanide in blood using head-space capillary gas chromatography (HS-GC) with nitrogen-phosphorus detection (NPD) was developed. The separation efficiency and sensitivity for hydrogen cyanide (HCN) were improved by using a GS-Q megabore capillary column and by injection of 500 μl of HS gas with a splitting ratio of 5. No interference or column deterioration was observed. Optimum HS conditions were found to be incubation of 50°C for 30 min in the presence of 10% phosphoric acid as an acidifying reagent. The distribution coefficient ( k) was 75.7 and 158.9 for HCN acetonitrile (CH 3CN; candidate for internal standard), respectively. HCN showed a different vaporization behaviour to CH 3CN with respect to temperature and matrix effect. The salting-out effect was relatively small for HCN and CH 3CN. An increase in the blood content in the liquid phase resulted in a significant increase in k for HCN. The calibration graph was linear over a wide concentration range of cyanide, and the limit of determination was 1 ng ml −1 (R.S.D. 10%). Because a considerable amount of CH 3CN was detected in control blood, the direct calibration method could be used instead of the internal standard method using CH 3CN. The detectable amount of cyanide was significantly decreased during the preincubation of cyanide and blood at 2°C. Thiocyanate in blood showed a positive interference. Contents determined by this HS-GC method agreed closely with those obtained by the microdiffusion-spectrophotometric method for blood samples from fire victims.