Analysis of polyfunctional thiols in beer : Developing a novel method of extraction and analysis using GC-FID

Abstract: In this project, attempts were made to identify and quantify two polyfunctional thiols – 4-mercapto-4-methyl-pentanone and 3-mercaptohexyl acetate – and three monoterpene alcohols – linalool, geraniol, and β-citronellol – in beer samples. In order to avoid the use of hazardous compounds such as dichloromethane and hydroxymercuriobenzoate, common in traditional methods, two novel techniques were tested: a pure liquid-liquid extraction of the beer samples with cyclohexane, and a liquid-liquid extraction with cyclohexane followed by solid phase extraction on silver ion columns. Analyses were then performed with GC-FID. Evaluation of the methods showed both to be insufficiently sensitive to measure the low concentrations of thiols in the beer samples. The complexity of the beer matrix also proved cumbersome, as the analyte peaks of the more abundant monoterpene alcohols in the chromatograms were often blotted out by non-analyte peaks. To improve this method towards thiol analysis, it is recommended to further enrich the extracts, such as by allowing the volatile solvent to evaporate and thereby increase the concentration of analyte in the remaining solvent, or to use a different detector such as a mass spectrometer or a sulfur chemiluminescence detector. To improve the methods towards monoterpene alcohols, it is recommended to use a column that more specifically retains the compounds of interest or use a slower temperature programme to improve resolution between peaks.