Abstract
A polarographic method for simultaneous determination of organic thiocyanate and isothiocyanate has been investigated. Benzyl thiocyanate (BTC) and benzyl isothiocyanate (BIT) were used as the representatives of organic thiocyanate and isothiocyanate, respectively. Both compounds are polarographically active, but their half-wave potentials are so close (the half-wave potential of BTC was-1.23 V vs. SCE and that of BIT was-1.21 V vs. SCE at pH 11.2) that the waves are inseparable from each other. Consequently, an indirect method was used, in which BIT was allowed to react with a primary or secondary amine. In this procedure the resulting thiourea showed the oxidation wave, and the unreacted thiocyanate gave the reduction wave.
The reaction of BIT and the amines, such as n-butylamine, iso-butylamine, n-dibutylamine, benzylamine, dibenzylamine, aniline, and sulfanilic acid, were tested. From the fact that n-butylamine was more reactive than the others, it was chosen as the suitable one. The effects of the concentration of n-butylamine and pH of the electrolytic solution were examined.
The recomended procedure is as follows; To a sample dioxane solution containing 10-210-3 mmol of each of BTC and BIT contained in a 10 ml measuring flask 0.5 ml of 1 M n-butylamine, 5 ml of the Britton-Robinson buffer (pH 7.0), and 0.1 ml of 0.1% gelatin solution are added. After the addition of a sufficient volume o dioxane to make its resulting concentration 30%, the solution is made up to 10 ml with distilled. water. An aliquot of the solution is placed in a polarographic cell and deoxygenated with nitrogen for 20 minutes at 25±0.1°C, then d. c. polarograms are recorded between 0 and-1.9 V vs. SCE.
The amounts of BTC and BIT were calculated from the respective calibration curves. The coefficients of variation of the present procedure were 3.3% for 5 × 10-4 M BTC and 2.2% for 5 × 10-4 M BIT. The results of analysis of γ-irradiated BTC containing BIT, which had been isomerized on irradiation, by the proposed method were in good agreement with those obtained by the gas chromatographic method.
