Application of synthetic benzoic acid technology in environmental radiocarbon monitoring

Environmental radiocarbon (¹⁴C) monitoring is gaining importance in China due to the recent rapid development of the nuclear industry. In this study, synthetic benzoic acid samples with the fingerprint of environmental ¹⁴C were generated by using the synthesis method, and the specific activity of ¹⁴C was determined using the liquid scintillation counting (LSC) method. The ultra-performance liquid chromatography (UPLC) analysis was performed in chemical properties test and results showed that the mean assay and yield of synthetic benzoic acid were 91.8% ± 2.4% and 84.5% ± 2.0%, respectively. Under adopted LSC counting conditions, the minimum detectable activity (MDA) of 64 Bq/kg C was achieved in our laboratory. The method's linearity was examined using a series of spiked samples, along with the ¹⁴C-free samples. The results showed a wide linear range up to 2000 Bq/kg C. Reproducible results were obtained from three batches of experiments with deviations in the intra-group and inter-group of 0.38%-3.06% and 1.24%-3.55%, respectively. Long-term evaluation of the system was found to be very stable (over 5 months storage) with the relative standard deviations of <1%. In addition, field applications in the vicinity of a nuclear power plant demonstrated that ¹⁴C data measured by our method was consistent with the accelerator mass spectrometry (AMS) method, suggesting the method's precision can meet the requirement of ¹⁴C monitoring near the nuclear facility. This is the first study to report the use of synthetic benzoic acid in environmental ¹⁴C monitoring, and it provides a new approach for improving the environmental ¹⁴C monitoring network.