D4 4 ethylphenol

The following chemicals were of analytical reagent grade. Eugenol, 4-methylsyringol, 4-ethylguaiacol, 4-ethylphenol and hydrochloric acid (HCl) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Guaiacol, o-cresol, p-cresol, and m-cresol were obtained from TCI America (Portland, OR, USA). 4-methylguaiacol and syringol were purchased from Alfa Aesar (Tewksbury, MA, USA). Deuterated standards d3-guaiacol, d3-4-methylguaiacol, d7-o-cresol, d7-p-cresol, d7-m-cresol, d5-4-ethylguaiacol, and d4-4-ethylphenol were obtained from CDN Isotopes (Pointe-Claire, QC, Canada) and d6-syringol was purchased from EPTES (Vevey, Switzerland). Solvents ethyl acetate (EtOAc) and pentane were of HPLC grade and purchased from Millipore Corporation (Darmstadt, Germany) and Sigma-Aldrich (St. Louis, MO, USA), respectively. HPLC-grade ethanol used in this study was from Sigma-Aldrich (St. Louis, MO, USA). Water was produced by a Milli-Q Element system (Millipore, Rockville, MD, USA).

Analytical grade volatile phenols (guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-ethylphenol, o-cresol, m-cresol, p-cresol, and eugenol) and deuterated NMR solvents (d₆-ethanol, D₂O, and DCl) were purchased from Sigma-Aldrich (Castle Hill, NSW, Australia). Deuterium-labelled internal standards (d₃-guaiacol, d₃-4-methylguaiacol, and d₄-4-ethylphenol) were sourced from CDN Isotopes (Pointe-Claire, Quebec, Canada). Analytical grade ethanol, tartaric acid, and sodium hydroxide were purchased from Thermo Fisher Scientific (Waltham, MA, USA). Food grade (>98% purity) α-, β-, and γ-CDs were supplied by IMCD Group (Adelaide, SA, Australia). Model wine was prepared by dissolving tartaric acid (5 g/L) in aqueous ethanol (12% alcohol by volume) and adjusting the pH to 3.5 by dropwise addition of 1 M sodium hydroxide. Stock solutions of internal standards and volatile phenols were prepared volumetrically in absolute ethanol and stored at −20 °C, with working solutions prepared in model wine and stored at 4 °C.