Chromatographic analysis of methylglyoxal and other α-dicarbonyls using gas-diffusion microextraction

Many α-dicarbonyl compounds such as methylglyoxal, diacetyl and pentane-2,3-dione are important quality markers of processed foods. They are produced by enzymatic and chemical processes, the Maillard reaction is the most known chemical route for α-dicarbonyl formation. In the case of methylglyoxal, there are obstacles to be overcome when analysing this compound due to its high reactivity, low volatility and low concentration. The use of extraction techniques based on the volatilization of methylglyoxal (like solid-phase microextraction) showed to be ineffective for the methylglyoxal extraction from aqueous solutions. Therefore, derivatization is typically applied to increase analyte's volatility. In this work a new methodology for the extraction and analysis of methylglyoxal and also diacetyl and pentane-2,3-dione from selected food matrices is presented. It is based on a gas-diffusion microextraction step followed by high performance liquid chromatographic analysis. It was successfully applied to port wines, black tea and soy sauce. Methylglyoxal, diacetyl and pentane-2,3-dione were quantified in the following concentration ranges: 0.24-1.74 mg L(-1), 0.1-1.85 mg L(-1) and 0.023-0.15 mg L(-1), respectively. The main advantages over existing methodologies are its simplicity in terms of sample handling, not requiring any chemical modification of the α-dicarbonyls prior to the extraction, low reagent consumption and short time of analysis.