## 2 Results and Discussion
### Ratio Analysis  
It was shown that different sulfur compounds were not affected by ethanol concentration in the same way. This causes an issue with wine analysis, where two different wines could have up to a 20-30% difference in ethanol concentration, or even more so if brandies or other spirits are involved. However, calibration and quantification rely on the ratio of analytes to internal standards. If an internal standard is selected that most closely mimics the behavior of an analyte in question, its ratio, at constant concentrations of both, will be constant despite an increase in ethanol. Thus, proper internal standards are necessary for accurate quantification. EMS and DIDS have been used as internal standards to measure smaller (DMS, thioacetates, etc.) and larger (DEDS, DMTS) compounds respectively [8; 14], though other compounds have been used, including hexylmercaptan, propylthioacetate [11], 4-methylthiobutanol [8], thiophene [15], etc. In addition to the traditional EMS and DIDS, this study used the internal standards DES, MIS, and EIS. These sulfides were selected for the protective nature of their large substituents, in an effort to reduce the outside influence on the central sulfur atom. Diisopropyl sulfide (DIS) was attempted to be used, however, it co-eluted with ethanol, causing an irregular peak due to quenching effects. The results from the analyte-to-internal-standard ratio tests on Carboxen-PDMS fiber are shown in Figure 4. As the Carboxen-PDMS fiber had the greatest sensitivity, and the ratios were at least as consistent as the other fibers, it was decided to only pursue a single fiber for analysis. DMS is most closely matched by EMS, as indicated by a flat curve shape throughout the increase of ethanol concentration. However, all other analytes show a large discrepancy when compared to EMS. The data suggest that DMDS and the thioacetates may be better suited with DES or EIS. DEDS and DMTS seem to most closely follow DIDS. H\({}_{2}\)S and MeSH, counter-intuitively, seem to follow DIDS, rather than EMS, as might be expected from their size. The direct analysis curves of H\({}_{2}\)S, MeSH, and DIDS show a similar gradual decrease with rising ethanol concentration, suggesting a less extreme influence. This may be a function of molecular size and displacement on the SPME fiber. For instance, DIDS is a relatively large compound that could displace smaller compounds, and H\({}_{2}\)S and MeSH are small enough to fit in the minute pores of the Carboxen phase and avoid displacement. This could decrease the effect of ethanol competition for both, as more mid-sized compounds may lack the ability to displace ethanol or remain on the fiber against larger compounds. Furthermore, between 0.0% and 1.0% ethanol, all ratios are unstable. This suggests a minimum of 1.0% ethanol is required for accuracy, above which the ratios become more consistent. Figure 4: Analyte to internal standard ratios (based on square roots of peak areas) to each of the five internal standards of DMS, DMDS, MeSOAc, EtSOAc, DEDS, DMTS, H\({}_{2}\)S, and MeSH on Carboxen/PDMS fiber. Similar effects were seen using the DVB-Carboxen-PDMS and DVB-PDMS fibers (data not shown). However, because the sensitivity was greatest on the traditional Carboxen-PDMS fiber, and as the ratio analysis suggests accurate measurements within defined ethanol ranges, it was decided to pursue the single fiber for further analysis. Based on the apparent stabilization above 1% EtOH, the ideal wine sample would be diluted to 2 mL wine:8 mL saturated salt water. Wine commonly ranges between 12-15% ethanol, which, after dilution, is reduced to 2.4-3%. It is within this range that analyte to internal standard ratios are best maintained, especially in the case of H\({}_{2}\)S and MeSH, in which a consistent correlation was not found across the entire ethanol range. Thus, in order to avoid strong ethanol matrix effects, internal standards EMS, EIS, and DIDS should be used on Carboxen-PDMS fiber.