A simple, rapid and sensitive semimicro method for the measurement of cyanide in blood

Conventional methods do not meet the clinical need for rapid cyanide measur ements. We report a procedure which can provide a result in 10 min. It shou ld be of particular interest to laboratories serving cardiac or renal units which use the hypotensive agent sodium nitroprusside, and burns units to w hich fire victims may be admitted suffering the effects of HCN from inhaled smoke. A sample of blood (100 mu L) is mixed with H3PO4, containing a surf actant, and the HCN is trapped in an alkaline mixture of 1,2-dinitrobenzene and 4-nitrobenzaldehyde in 2-methoxyethanol. The catalytic action of cyani de, which produces purple 2-nitrophenylhydroxylamine, is stopped with aceto ne after 6 min. The absorbance measured at 560 nm shows a linear relationsh ip with the cyanide concentration, but the slope varies with the ambient te mperature. Since KCN added to both 50 mmol/L NaOH and blood gives similar a ssay results, any inaccuracy arising from changes in temperature can be avo ided by running standards at the same time as the blood sample.