Development, validation and application of a specific method for the quantitative determination of wine esters by headspace-solid-phase microextraction-gas chromatography-mass spectrometry
Résumé
A method for specifically quantifying 32 apolar esters in wine is reported that employs head space solid phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC–MS). A dozen esters were studied for the first time in wines, among them methyl trans-geranate, never reported in red wines until now. The target esters were apolar but bore a broad range of functional groups and have concentrations ranging from mg/l to ng/l levels; polar esters being effectively extracted by dichloromethane. Extraction and desorption conditions were optimised to obtain the best compromise for the simultaneous analysis of all 32 studied esters. To provide specificity for the method, deuterated ethyl esters were used as internal standards. These were ethyl-d5 butyrate, hexanoate, octanoate and cinnamate, synthesised from the appropriate acyl chloride and ethanol-d6. The esters were quantified in the wines with satisfactory repeatability (1.8% < RSD < 11.2%), reproducibility (1.5% < RSD < 15%), sensitivity (0.4 ng/l < LOQ < 4 μg/l), accuracy and specificity. The validation was carried out with several wine types as matrices (red, dry and sweet white). The optimised method was applied to 19 French wines and the results confirmed some well established oenological principles and opened prospects for further study on wine esters that had not been previously measured.