Stable isotope ratio analysis combined with likelihood ratio as a new tool for establishing ethanol origin

Abstract

Blood alcohol concentration is an important objective basis in traffic accidents and accounts for the majority of forensic toxicology worldwide each year. The origin of ethanol detected in bio-samples has three possible origins: consumption, contamination or decomposition, which are frequently at the center of legal disputes. The stable carbon isotope is a value that can characterize the origin of a substance and has received increasing attention from forensic chemistry researchers in recent years. In a previous study, the stable carbon isotope of ethanol showed its potential for traceability; however, the overlap between the δ13C values of different ethanol origins gradually appeared as the sample size increased. In this study, 324 alcohol consumption samples (group A), 97 contamination samples (group B), and 26 decomposition samples (group C) were analyzed by gas chromatography-isotope ratio mass spectrometry. The δ13C values of the three groups ranged from –33.05 ‰ to −2.85 ‰ with different densities. The overlap interval of the groups ranged from 48.64 % to 56.69 % of the total. Based on the corresponding probability density curve, the likelihood ratio was used to describe the indication of ethanol origin. This study analyzed ten samples in real cases. Innovative pathway (stable carbon isotope -likelihood system) and traditional pathway (ethyl glucuronide-n-propanol system) were used to indicate the ethanol origin in the blood. This study demonstrates the feasibility and potential of combining stable isotope analysis with chemometrics to discriminate ethanol origin in alcohol-related cases and also provides new ideas to discriminate ethanol origin.