Novel method using o-hydroxyphenylthiourea for cadmium sensing in water samples †

Cadmium(II) catalyses dimerisation of o-Hydroxyphenylthiourea(OHPTU) to a yellow coloured disulphide, 1,1’-dithio-bis-N-(o-Hydroxyphenyl)formamide. Rate of formation of the coloured dimer increases with the concentration of cadmium(II) ions. Photometric and fluorometric methods were employed to study this reaction at pH 9.0 and the range of determination was determined to be 600ng.mL-1 - 30.0ng.mL-1 with a detection limit of 20.0ng.mL-1 using fixed time approach. The absorbance measurements were taken at λmax=416nm and the quenching effect of cadmium(II) on the fluorescence intensity of OHPTU was studied at λEm=520nm using Stern-Volmer plots. Effects of variation in analytical parameters and interference of associated metal ions in the catalysed oxidation of OHPTU were investigated. This method is fairly selective, sensitive, low in cost and free from pre-concentration procedures. The developed method was successfully applied to the determination of cadmium(II) present in stream water, ground water, fountain water, tap water and sludge water samples.