Determination of 232Th in urine by ICP-MS for individual monitoring purposes

Thorium is naturally occurring in various ores used for industrial purposes and has numerous applications. This paper sets out to investigate urine analysis as a suitable monitoring approach for workers potentially exposed to thorium, Due to its biokinetic behavior and its low solubility, urinary concentrations are generally very low, requiring therefore high sensitivity analytical methods. An analytical procedure has been developed for detecting Th-232 concentrations of below 1 mBq L-1 quickly and easily. Due to the long half-life (1.41 x 10(10) y) of Th-232, the potential of a procedure based on urine sample dilution and ICP-MS (inductively coupled plasma-mass spectrometry) measurement was investigated first. Two dilution factors were chosen: 100, which is more suitable for long-term measurement trials, and 20, which increases sensitivity. It has been shown that a 100-fold dilution can be used to measure concentrations of below 1 mBq L-1, whereas a 20-fold one ran be used to reach concentrations of below 0.06 mBq L-1. Then, on the basis of the limitation of the procedure based on urine dilution, the suitable field of application for the different procedures (100-fold and 20-fold dilution and also a chemical purification followed by an ICP-MS measurement) was determined in relation to monitoring objectives.