Validation of a colorimetric method for measuring urinary thiocyanates applicable to cyanide poisoning

Abstract

The aim of this work is the validation of a spectrophotometric method for the measurement of urinary thiocyanates. In acidic pH, thiocyanate ions give, with ferric nitrate, a red colour corresponding to 400 nm. The reagents required for the assay were: a stock solution of thiocyanate prepared by dissolving ammonium thiocyanate (NH4SCN) in distilled water, a solution of ferric nitrate [Fe(NO3)3, 9H2O] at 1% prepared by dissolving ferric nitrate in distilled water, a solution of hydrochloric acid (10%) prepared by diluting hydrochloric acid in distilled water. A standard calibration range and three validation ranges were prepared and analysed every day for three days. A total of 3 standard ranges and 9 validation ranges were performed. A blank is used to tare the absorbance to zero, treating a 1 mL blank urine, in the same way as the range points. The evaluation examined specificity, accuracy, fidelity and linearity. The Accuracy Profile was established with an acceptable deviation λ set at ± 15%. The probability β was set at 80%. The validated method is linear in the concentration range varying between 0.232 g/L and 0.5 g/L. The response function used is Y = a3X (The acceptable deviation λ has been set at ± 15%. The probability β has been set at 80%). The coefficient of variation (CV) of repeatability varies between 0.123 and 0.215%. The limit of quantification is 0.232 g/L. Cyanide is quickly converted by sulfurization to thiocyanate (SCN−). This is the main route of cyanide biotransformation. Thiocyanate is excreted primarily in the urine. This method, which is easy to implement in laboratories with limited resources and useful as a marker for acute cyanide poisoning, can be used as a diagnostic aid.