Rapid Determination of Thiourea in Waste Water by APCI Tandem Mass Spectrometry Using Selected Reaction Monitoring

Thiourea, a toxic substance for nitrification bacteria, active at low concentration levels (toxicity limit: 76 ppb), cannot be analysed by conventional methods. Its high solubility in water and insolubility in non-polar organic solvents, such as diethyl ether or dichloromethane, make its extraction impossible. A rapid method for the direct determination of thiourea in waste water with a minimal sample pre-treatment by atmospheric-pressure chemical ionisation mass spectrometry is presented here. The method takes advantage of tandem mass spectrometry with selected-reaction monitoring so that the system acts as a completely specific detector for thiourea. A detection limit of 1 ppb has been obtained and linear calibration has been determined in the concentration range 10-5000 ppb. The reliability of the method was tested by the analysis of spiked samples, showing good accuracy. The method also proved its ruggedness in the analysis of real samples, giving very good results, despite the complexity of the matrix.