Method validation for determination of ¹⁴C with the use of CO₂ absorption method

The CO₂ absorption method is applicable for analyzing radiocarbon content in environmental samples. Since this method is characterized with low accuracy and sensitivity, optimization and improvement are needed. In the Laboratory for Liquid Scintillation Spectrometry at Jožef Stefan Institute, internal method validation was performed. The main aim of this validation was to set optimal and controlled conditions that would improve the total uncertainty. For that purpose, we investigated the effect of three parameters on the final results: size of the trap, flow rate and combination of trapping mediums. All measurements were performed on ultra-low level liquid scintillation counter Quantulus™ 1220. The counting efficiency was determined with the use of the external standard method (SQP(E)) and standard addition method. We recognized the use of a big trap, thus use of a balance with a readability of 0.01 g, as the most significant contributor to the total uncertainty. A small trap, flow rate of 0.1 L/min and a mixture of CarbonCount™ and CarbonTrap™ proved to be the most suitable parameters. Using a small trap instead of a big one lowered the relative uncertainty from 2.4% to 0.01%, causing a decrease in the total uncertainty from 4.7% to 3.2%.