Quantitative determination of 4-ethylphenol and 4-ethyl-2-methoxyphenol in wines by a stable isotope dilution assay

The deuterium-labelled standards 4-ethylphenol-d3 and 4-ethyl-2-methoxyphenol-d3 were synthesized and utilized in a rapid, sensitive, and accurate stable isotope dilution assay for 4-ethylphenol and 4-ethyl-2-methoxyphenol in wine. For a 5-mL sample of a Merlot wine, quantitation was reliable down to 500 ng/L for 4-ethylphenol and 100 ng/L for 4-ethyl-2-methoxyphenol at estimated signal-to-noise ratio of 3:1, respectively. The concentrations of 4-ethylphenol and 4-ethyl-2-methoxyphenol were also measured in 54-barrelled red commercial wines from the Okanagan Valley in British Columbia. The results indicate significantly different internal standard recoveries for the two analytes, demonstrating the need for individual stable isotope derivatives to reliably quantitate 4-ethylphenol and 4-ethyl-2-methoxyphenol in wines.