The Effects of Sample Preparation and Gas Chromatograph Injection Techniques on the Accuracy of Measuring Guaiacol, 4-Methylguaiacol and Other Volatile Oak Compounds in Oak Extracts by Stable Isotope Dilution Analyses

Abstract

The deuterium-labeled standards [(2)H(3)]-guaiacol and [(2)H(3)]-4-methylguaiacol were synthesized and utilized in a method employing gas chromatography-mass spectrometry to determine the concentration of guaiacol and 4-methylguaiacol in wine or extracts of oak shavings. The method was combined with previously published methods for 4-ethylphenol, 4-ethylguaiacol, cis- and trans-oak lactone and vanillin, so that all these compounds could be quantified in a single analysis. The method can employ either liquid-liquid extraction or headspace solid-phase microextraction (SPME) and is rapid, robust, precise, and accurate. Under certain conditions, there was artifactual generation, to varying degrees, of guaiacol, 4-methylguaiacol, cis-oak lactone, and vanillin during the analysis of oak extracts, especially when diethyl ether extraction and injector block temperatures at or above 225 degrees C were employed. The most substantial effects were observed for guaiacol, in which results could be exaggerated by over 10 times. These artifacts could be avoided by using headspace SPME or by preparing liquid-liquid extracts with pentane or pentane/diethyl ether (2:1) injected at 200 degrees C providing spot checks using headspace SPME were performed. Data obtained for previously published quantitative determination of guaiacol in oak extracts should be reexamined carefully, with special attention paid to their respective methods of sample preparation and analysis.

Phenolic and furanic compounds of Portuguese chestnut and French, American and Portuguese oak wood chips

“…Since extractions are done at elevated temperatures, thermal degradation is a potential concern. Pollnitz et al [12] have reported, for some volatiles compounds extracted from oak wood, artifacts formation due to the high injector temperature used for GC-MS analysis or the high temperature and relatively polar solvent used on PLE. We did not observe any artifacts, and most of the compounds identified have already been detected, in similar samples, using others extraction techniques [3,7,33,34].…”

“…The toasting level of wood plays a significant role on wine aging. In fact, during the heating treatment, large wood polymers such as lignin or cellulose and hemicelluloses [12] are fragmented by high temperature, and many compounds such as phenols, phenolic aldehydes, furanic derivatives and lactones are formed and transferred to the wine [6]. Thus, the study of the interaction between wood species and toasting levels is of great importance, in order to establish its influence on wine properties.…”

Aroma‐active compounds of American, French, Hungarian and Russian oak woods, studied by GC–MS and GC–O

“…Guaiacol, together with other volatile oak compounds, can be generated during the analysis of oak extracts by GC, especially when the injector temperature is >225°C. 23 Other volatile compounds identified in non-toasted oak wood were nonanal, trans-2-nonenal and decanal. These compounds can transmit unpleasant aromas to the wine, such as the 'sawdust' aroma of dry wood that is perceptible in some wines aged in new barrels.…”

The effect of winemaking techniques on the intensity of smoke taint in wine

“…The internal standards were prepared as previously described (Dungey et al 2011). Guaiacol and 4-methylguaiacol concentrations were determined using an Agilent 6890N gas chromatograph coupled to a 5975 inert source mass spectrometer and stable isotope dilution assay methods reported previously (Pollnitz et al 2000(Pollnitz et al , 2004. The analysis was performed by the Australian Wine Research Institute's Commercial Services Laboratory (Adelaide, Australia).…”

“…Oak or tannin additives increased guaiacol and 4-methylguaiacol concentrations, with greater contributions from oak treatments, including oak-derived Tannin 4, compared with tannin treatments. However, this is not surprising given that guaiacol and 4-methylguaiacol are known oak volatiles (Pollnitz et al 2004, Garde-Cerdán et al 2008, Rodriguez-Bencomo et al 2009). Guaiacol glycoconjugate concentrations were approximately 10% higher in control wines than oak-or tannin-treated wines; possibly indicating some adsorption of glycoconjugates by the oak and tannin.…”