A colourimetric procedure for the determination of thiocyanate in plasma

A colourimetric method is described for the determination of thiocyanate using a modification of the König reaction. The reagents used are stable, relatively non-toxic, and produce a colour with lambda max 543 nm which is stable for at least 90 minutes after formation. Although the method requires only 0.1--0.5 mL of plasma, 0.25 mg/L of thiocyanate may be determined using this procedure. The calibration curve is linear to at least 60 mg/L and is highly reproducible. Plasma samples analysed on a within-day (10.0 mg/L) and between-day (4.9 mg/L) basis, had coefficients of variation (CV) of 2.39% and 3.09%, respectively. Recovery of thiocyanate added to plasma is quantitative.