Vapour phase Fourier transform infrared spectrometric determination of thiourea

Abstract

A novel and precise procedure for the determination of thiourea based on vapour-generation Fourier transform infrared spectrometry is described. A 4 ml volume of 1.4% m/v iodine solution was injected into a glass vessel containing 5 ml of thiourea and 0.2 ml of l M sodium hydrogencarbonate solution. The CO₂ evolved under these conditions was swept by a stream of nitrogen to an infrared gas cell. At 200 s after injection of the iodine solution, the vapour phase FTIR spectra were continously recorded, as a function of time, between 2500 and 2200 cm⁻¹, which includes the CO₂ absorption band at 2350 cm⁻¹. From the absorbance data in the 2399–2284 cm⁻¹ range, integrated absorbance measurements were obtained providing transient recordings which correspond to the absorbance of CO₂ in the selected wavenumber range. The method provided a limit of detection of 10 ppm of thiourea, a throughput of 14 samples h ⁻¹ and an RSD of 1.1% for three independent analyses of a 500 ppm thiourea solution. Results obtained for a series of real samples compared well with those obtained using potentiometric titration as a reference method.