Determination of 99Tc in urine by liquid scintillation counting to evaluate internal contamination

A practical method is described which allows the radiochemical determination of 99Tc in urine. The radionuclide is recovered as tetraphenylarsonium pertechnetate by coprecipitation with tetraphenylarsonium perchlorate and its activity is counted by the liquid scintillation technique. The lower limit of detection, assumed equal to three standard deviations of the blank activity, is about 2 pCi in 50 ml of urine and permits an evaluation of an internal contamination of one investigation level even four months after intake. The urinary excretion function of 99Tc is calculated from experimental data reported in the literature for (95m)Tc and is used to establish investigation levels on the basis of annual limits on intake recommended by the International Commission on Radiological Protection. The illustrated method is sensitive enough to perform accurate evaluations every three months, a frequency suitable for radiological protection of workers.