Alcohol congener analysis in a forensic context: detection of iso-α-acids to confirm beer consumption

Alcohol abuse is a leading factor in many crimes and accidents with beer being the oldest and most widely consumed alcoholic beverage in the world. This research has focused on iso-α-acids (IAA) derived from the hop plant (Humulus lupulus L.) used in brewing and found in beer. Additionally, three structurally similar but chemically-altered IAA known as “reduced IAA” (rho-, tetrahydro- and hexahydro-IAA), are also beer-specific ingredient congeners found in beer, specifically used in green or clear bottled beer. A protein precipitation extraction and ESI-UHPLC-MS/MS method was developed and validated for the detection of these compounds in biological specimens that can confirm beer consumption. The long-term stabilities of these analytes in stored blood specimens was assessed over 8 weeks with freezing (-20 °C) and refrigeration (4 °C) conditions determined as acceptable. The analysis of blood and urine collected over 6 hours from volunteers given five different beers in five drinking studies separated by at least one week. The natural and reduced IAA were found to be bioavailable, show small inter-variable differences in concentration-time profile, and possess pharmacokinetic data such as quick absorption rates and half-lives ranging between ~30-46 minutes. Furthermore, in the assessment of 130 postmortem cases, ~57% of positive BAC cases showed beer consumption prior to death, and an even higher prevalence (87%) in casework where “beer” was mentioned in the case circumstances. Considerable postmortem redistribution, a serum to blood ratio of ~3 and a weak association between BAC and IAA groups was observed. Vitreous humour and urine specimens contained very low concentrations and prevalence of IAA groups. Lastly, the analytical method was used to assess the IAA profiles for over 30 different brown, green and clear bottled, local and international beers. This reference catalogue assists forensic toxicologists in comparing and interpreting the results of authentic and unknown casework. This novel approach can be used to provide important information on the drinking behaviour and circumstances surrounding after-drinking (hip-flask) defence cases and additional forensic applications such as coronial, drug facilitated sexual assault, research or clinical medico-legal casework. Thesis by publication is the primary structure of this PhD thesis with a total of seven peer-reviewed publications (three in review) resulting from this project that providing comprehensive knowledge for the use of this technique in forensic institutes locally and internationally.