High Throughput, Direct Determination of 226Ra in Water and Digested Geological Samples

Abstract

A method was developed for direct measurements of 226Ra in water samples with triple quadrupole inductively coupled plasma mass spectrometry (ICP-QQQ). The limit of detection was 0.42 pg L-1226Ra (15 mBq L-1, 0.42 pCi L-1), which is compliant with the specifications for methods used for routine analysis of drinking water quality according to European and U.S. regulations. The use of N2O as reaction gas ensured that no separation before analysis was necessary. Water samples with high total dissolved solids (conductivity >100 mS cm-1) were also successfully analyzed after a simple dilution, yet the associated detection limit was higher (17 pg L-1, 0.61 Bq L-1, 16 pCi L-1). 226Ra content in soil and rock samples was determined with the same method after acid (HNO3 + H3PO4) digestion and dilution, resulting in a limit of detection of 0.75 ng kg-1 (27 Bq kg-1, 0.74 nCi L-1). Analysis of water samples was achieved within 2 min on a running instrument, while the preparation and analysis of 15 geological samples can be completed in 3 h. The key advantages of this direct analysis method are short preparation time, low labor intensity, low sample input (2 mL for water samples, 0.2 g for geological material), high sample throughput (2 min sample to sample, >150 samples measured in 8 h), and use of standard ICP-QQQ hardware. Overall, the proposed method offers a new opportunity for measuring a large number of samples with minimal effort and, in turn, for improving emergency preparedness, environmental monitoring, and data collection for environmental modeling.