ABSTRACT
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.
ABSTRACT
The QuEChERS methodology has been used for the determination of pesticides in solid samples. However, this technique can be equally useful for other applications, namely for liquid samples. This work presents a new application of QuEChERS to the analysis of important ageing markers in beverages, the volatile phenols, by liquid chromatography with fluorimetric and UV detection. The sample preparation methodology comprises two sequential steps: (1) salting-out liquid-liquid extraction and (2) dispersive solid-phase extraction for extract clean-up. The methodology showed good repeatability (ca. 3%) and reproducibility (ca. 6%) with recovery levels above 90% and limits of detection varied in the range of 0.001-0.055 mg L(-1). A variable amount of phenols was found in the analysed samples (beers, wines and fruit juices), being 4-ethylphenol and 4-ethylguaiacol the compounds found in higher amounts, varying in the range of 0.12-1.11 mg L(-1) and 0.13-1.23 mg L(-1), respectively.