Development of a LC/MS Method for Analysis of Total Vicinal Diketones in Beer. Maxime Blanchette, Barry van Bergen, and John D. Sheppard (1), Department of Bioresource Engineering, Macdonald Campus of McGill University, Ste-Anne-de-Bellevue, Quebec, Canada. (1) Corresponding author. Department of Food Science, Campus Box 7624, North Carolina State University, Raleigh 27695; E-mail: <jdsheppa@ncsu.edu> J. Am. Soc. Brew. Chem. 65(2):70-76, 2007.

A liquid chromatography/mass spectrometry (LC/MS) method was developed for the simultaneous determination of vicinal diketones (VDK), diacetyl and pentanedione, in beer. Diacetyl and pentanedione were derivatized with o-phenylenediamine (OPDA) to form quinoxaline compounds. Total VDK were measured directly over a concentration range of 10 µg/L to 10 mg/L with less than 10% variation. The reaction of VDK with OPDA was studied to optimize reaction time. Decarboxylation of the diacetyl precursor alpha-acetolactate was evaluated using two decarboxylation techniques. Attempts to simultaneously determine the amino acids leucine, isoleucine, and valine as well as the VDK in beer were successful, but only for amino acid concentrations up to 10 mg/L. Because levels of amino acids found in wort are generally higher than this, sample dilution and separate injections were required. Samples were collected from a local commercial brewery and analyzed for total VDK to further evaluate the method’s practical application. Keywords: Amino acids, Decarboxylation, LC/MS, o-Phenylenediamine, Vicinal diketones