Radiocarbon-based direct liquid scintillation counting method to quantify biogenic carbon and fossil-derived...

Adulteration of natural bio-based products with petrochemical-derived synthetic alternatives poses potential human health and environmental hazards. Rapid, cost-effective methods for quantifying biogenic content and synthetic adulterants are beneficial for regulatory compliance and product authentication. We report a radiocarbon-based direct liquid scintillation counting (LSC) instrument method for quantifying biogenic content and synthetic adulterants in essential oils. Samples are mixed with a scintillator and analysed by LSC to determine the ¹⁴C specific activity. A calibration curve was established using 100% pure and biogenic essential oils from multiple species and applied to determine the biogenic content of the essential oils under examination. Validation of the method was performed via accelerator mass spectrometry (AMS), with percent modern carbon (pMC) values from the direct LSC method deviating by ≤3.7% from AMS measurements, and relative standard deviation (RSD) and relative error (RE) values of ≤2.0%. The method allows the analysis of up to 6.8 g of carbon (10 ml of sample, 0.86 g mL^-1). The minimum detection level across different quench levels was 0.58 ± 0.12 pMC for a counting time of 300 min, demonstrating the ability to quantify trace levels of adulterants and representing a 8.4-fold improvement over the CO₂ absorption and LSC method. A method is also described for converting unsaturated functional groups, such as aldehydes or ketones, to their saturated forms using NaBH₄ reduction, thereby rendering the oil suitable for direct LSC analysis. Analysis of several essential oils confirmed the robustness and accuracy of the method. Owing to its rapidity, low cost, and several advantages over other methods, the direct LSC method merit consideration for future review and standardisation for possible incorporation into ASTM test methods, facilitating reliable quality control and the global export of essential oils.