Concurrent Determination Of Ra-224, Ra-226, Ra-228, And Unsupported Pb-212 In A Single Analysis For Drinking Water And Wastewater: Dissolved And Suspended Fractions

A technique has been developed for the measurement of Ra-224, Ra-226, Ra-228, and unsupported Pb-212 concurrently in a single analysis. The procedure can be applied to both drinking water and wastewater, including the dissolved and suspended fractions of a sample. For drinking water samples, using 3-L aliquots, the radium isotopes are isolated by a fast PbSO4 co-precipitation and then quantified by gamma-ray spectroscopy. The radium isotopes Ra-224, Ra-226, and Ra-228 are measured through their gamma-ray-emitting decay products, Pb-212, Pb-214 (and/or Bi-214), and Ac-228, respectively. Because of the short half-life of Ra-224 (T-1/2 = 3.66 d), the precipitate should be counted within 4 d of the sample collection date. In case the measurement of unsupported Pb-212 (T-1/2 = 10.64 h) is required, the gamma-ray analysis should be initiated as soon as possible, preferably on the same day of collection. The counting is repeated after about 21 d to ensure the Ra-226 progeny are in equilibrium with their parent. At this point, the Ac-228 equilibration with its Ra-228 parent is already established. In the case of samples containing suspended materials, an aliquot of sample is filtered and then the filtrate is treated as described above for drinking water samples. The suspended fraction of sample, collected on the filter, is directly analyzed by gamma-ray spectroscopy with no further chemical separation. Aliquots of de-ionized water spiked with various radium standards were analyzed to check the accuracy and precision of the method. In addition, analysis results of actual samples using this method were compared with the ones performed using U.S. Environmental Protection Agency-approved procedures, and the measured values were in close agreement. This method simplifies the analytical procedures and reduces the labor while achieving the precision, accuracy, and minimum detection concentration requirements of EPA's Regulations.