Determination of trace amounts of thiocyanate by a new kinetic procedure based on an induction period

A new, simple and sensitive kinetic spectrophotometric method with no need for removing of interfering substances is proposed for the determination of thiocyanate ion in biological and water samples. The procedure is based on the inhibiting effect of thiocyanate on the sodium periodate–potassium bromide–meta cresol purple (MCP) system in acidic media. The induction period of the reaction is proportional to the SCN− concentration. The decolorization of meta cresol purple by the reaction products was used to monitor the reaction spectrophotometrically at 525 nm. Under optimum conditions, thiocyanate can be determined in the range of 0.02–0.8 μg ml−1 with a 3σ detection limit of 5 ng ml−1. The relative standard deviations for 10 replicate determinations of 0.060, 0.10 and 0.50 μg ml−1 thiocyanate are 3.7, 2.4 and 1.0%, respectively. This method has been successfully used to the determination of thiocyanate content in smokers and non-smokers saliva and spiked water sample.