Improving headspace-solid-phase microextraction of 3-isobutyl-2-methoxypyrazine by experimental design with regard to stable isotope dilution gas chromatography-mass spectrometric analysis of wine

To solve problems of sensitivity, repeatability and multi-step extraction related to 3-isobutyl-2-methoxypyrazine (IBMP) determination in wines, a simple method based on the novel combination of solid-phase microextraction and stable isotope dilution assay is presented. Among the parameters that affect this type of extraction, five of them have been optimised since the other parameters have common values or do not require optimisation (e.g. addition of sodium chloride at saturated concentration) and so were fixed. Vial volume, sample volume/vial volume ratio, pH, adsorption time and temperature have been optimised by means of two experimental designs. After extraction, quantification was performed by stable isotope dilution with gas chromatography-tandem mass spectrometry ([]-IBMP as internal standard). The final procedure allowed quantification far below IBMP’s sensory threshold (1 ng l⁻¹ versus 15 ng l⁻¹) with a 4% standard deviation. This method has been applied to experimental Fer servadou wines. Comparison of IBMP contents confirmed the efficiency of some viticultural and enological techniques on the herbaceous flavour decrease, such as prior fermentation maceration at high temperature (70 °C) and the use of a reflective carpet on viticultural soil.