The present work describes a simple and straightforward methodology for the determination of α-ketoglutaric acid (KA) and pyruvic acid (PA) in beer. This work involves three basic steps: (a) cleaning of the sample by solid phase extraction (SPE); (b) α-ketoacids' derivatization with o-phenylenediamine (OPDA) to form quinoxalines; and (c) separation and detection of the quinoxalines by high-performance liquid chromatography with spectrophotometric detection (HPLC-UV). The identity of the eluted compounds was also confirmed by high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) in the positive ion mode. The developed methodology showed good repeatability (ca. 4%) and linearity as well as good limits of detection (0.091 and 0.055 mg L−1 for KA and PA, respectively) and quantification (0.30 and 0.18 mg L−1 for KA and PA, respectively). To sum up, the goal of this technical note is to develop a single HPLC procedure with previous SPE clean up suitable to use in routine analysis laboratories.
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Montenegro et al. (2011) studied this question.