Ultrasound-assisted emulsification–microextraction for the sensitive determination of Brett character responsible compounds in wines

In this study, a method based on ultrasound-assisted emulsification–microextraction (USAEME) was optimised for the determination of Brett character responsible compounds (4-ethylguaiacol (EG), 4-ethylphenol (EP), 4-vinylguaiacol (VG) and 4-vinylphenol (VP)) in wines. For this purpose, once the extraction solvent had been selected, the influence on the extraction efficiency of ratio between extraction solvent and sample volumes, temperature, ionic strength and time was studied using experimental design methodology. The optimum conditions found for USAEME of 5 mL of wine were 160 μL of chlorobenzene at 60 °C during 5 min without salt addition. Then, the analytical performance of the optimised USAEME procedure was evaluated. For all the studied compounds, the proposed method showed correlation coefficients over 0.984. Satisfactory repeatability (below 10%) and inter-day repeatability (below 11%) were obtained at different concentration levels and the method achieved detection limits similar or even lower than previously reported for these compounds in wines. Moreover, the applicability of the method was evaluated by the analysis of real samples. To our knowledge, this is the first time that USAEME has been applied to the determination of Brett character responsible compounds in wine.