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^{-1 226}Ra (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.