Accelerator mass spectrometry and benzene synthesis coupled with liquid scintillation spectrometry are often used for accurate measurements of ¹⁴C activity in the environmental matrices. Thermal oxidation is one of the methods employed for ¹⁴C determination in environmental matrices. In this method, the sample is oxidised at high temperature (600–900 °C) to convert carbon species to CO₂ and trapped in an amine-based absorber for determining the activity in a liquid scintillation counting (LSC) system. In this study, the performance of a commercially available tube furnace system (pyrolyser), for batch combustion of samples, was evaluated for the determination of ¹⁴C specific activity in terrestrial biota samples. Significant improvements over the manufacturer specified method, which is primarily designed for analysis of samples with activity well above the environmental background level, was implemented to achieve accurate determination of ¹⁴C specific activity at ambient background level. In the improved method, the CO₂ produced from the combustion of the sample was isolated from the combustion products through cryogenic trapping and then absorbed in the absorber (Carbo-Sorb E) through a simple off-line transfer process. This allowed (i) optimisation of CO₂ absorption by the absorber (2.2477 g of CO₂/10 mL), (ii) achieving good accuracy and precision in the measurements, and a minimum detectable activity value of 13 Bq kg⁻¹C for a counting time of 300 min (7 Bq kg⁻¹C for 1000 min), (iii) avoiding uncertainty associated with the determination of recovery of ¹⁴C in the combustion and trapping process, and (iv) elimination of the need for an independent determination of carbon content (%) for expressing the results in terms of ¹⁴C specific activity. The method is capable of yielding accurate results with a deviation of <2.4% from the target value for IAEA C3 quality assurance reference material (with a relative standard deviation of 1.40%, and relative error of 0.34%). The combined uncertainty (1σ) associated with the measurements was computed to be 3.4%. Upon optimisation, the suitability of the method for the determination of ¹⁴C specific activity in typical terrestrial biota samples of clean air region (region not affected by local anthropogenic sources) and for the quantification of a small increase in the ¹⁴C activity above ambient levels in the vicinity of a nuclear power plant is demonstrated.

促进剂质谱和苯合成与液体闪烁光谱结合经常用于环境基质中¹⁴ C活性的准确测量。热氧化是在环境基质中测定¹⁴ C的方法之一。在这种方法中，样品在高温（600–900°C）下被氧化，将碳物质转化为CO _2，并被捕集在基于胺的吸收剂中，以测定液体闪烁计数（LSC）系统中的活性。在这项研究中，评估了用于样品批量燃烧的市售管式炉系统（热解炉）的性能，以确定¹⁴陆地生物区系样品中的C比活。对制造商指定的方法进行了重大改进，该方法主要用于分析活性远高于环境背景水平的样品，旨在准确测定环境背景水平下的¹⁴ C比活度。在改进的方法中，通过低温捕集将样品燃烧产生的CO ₂与燃烧产物分离，然后通过简单的离线传输过程将其吸收到吸收塔（Carbo-Sorb E）中。这允许（i）优化吸收塔对CO ₂的吸收（2.2477 g CO ₂/ 10 mL），（ii）在测量中达到良好的准确性和精密度，并且在300分钟的计数时间内的最低可检测活性值为13 Bq kg ^-1 C（1000分钟为7 Bq kg ^-1 C），（ iii）避免在燃烧和捕集过程中确定¹⁴ C的回收率时存在不确定性，并且（iv）无需为了确定^14中的结果而独立确定碳含量（％）C特定活动。该方法能够产生准确的结果，与IAEA C3质量保证参考材料的目标值之间的偏差为<2.4％（相对标准偏差为1.40％，相对误差为0.34％）。与测量相关的组合不确定度（1σ）计算为3.4％。经优化后，该方法适用于确定清洁空气区域（不受当地人为源影响的区域）的典型陆地生物群样品中¹⁴ C比活度以及定量高于环境水平的¹⁴ C活度的小幅增加在核电厂附近进行了演示。