The effect of wine matrix on the analysis of volatile sulfur compounds by solid-phase microextraction-GC-PFPD

Graduation date: 2012Constituents of the wine matrix, including ethanol, affect adsorption of sulfur volatiles on solid-phase microextraction (SPME) fibers, which can impact sensitivity and accuracy of volatile sulfur analysis in wine. Several common wine sulfur volatiles, including hydrogen sulfide (H2S), methanethiol (MeSH), dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), diethyl disulfide (DEDS), methyl thioacetate (MeSOAc), and ethyl thioacetate (EtSOAc), have been analyzed with multiple internal standards using SPME-GC equipped with pulsed-flame photometric detection (PFPD) at various concentrations of ethanol, volatile-, and non-volatile-matrix components in synthetic wine samples. All compounds exhibit a stark decrease in detectability with the addition of ethanol, especially between 0.0 and 0.5%v/v, but the ratio of standard to internal standard was more stable when alcohol concentration was greater than 1%. Addition of volatile matrix components yields a similar decrease but the standard-to-internal-standard ratio was consistent, suggesting the volatile matrix did not affect the quantification of volatile sulfur compounds in wine. Non-volatile wine matrix appears to have negligible effect on sensitivity. Based on analyte:internal standard ratios, DMS can be accurately measured against ethyl methyl sulfide (EMS), the thioacetates and DMDS with diethyl sulfide (DES), and H₂S, MeSH, DEDS, and DMTS with diisopropyl disulfide (DIDS) in wine with proper dilution. The developed method was then used to quantify sulfur compounds in 21 various California wines. H₂S and MeSH were found in higher concentrations in white varietals, while DMS was slightly higher in red varietals, particularly cabernet sauvignon and merlot. Trace amounts of DEDS and MeSOAc were found in almost all wines. DMS and DMTS were found in all wines, in some instances above reported thresholds