Intelligent use of ethanol for the direct quantitative determination of methanol in alcoholic beverages

A gas chromatography flame ionization detector (GC-FID) method based on the use of ethanol as an internal standard was developed and in-house validated for the direct determination of methanol in ethanol containing products (alcoholic beverages and rectified ethyl alcohol) with ethanol concentrations from 6.5 % to 96.6 % by volume. Validation of the method was performed in terms of linearity, limit of detection (LOD), limit of quantification (LOQ), recovery, repeatability, intermediate precision, trueness, uncertainty and matrix effect. The method showed satisfactory results, considering the parameters of linearity (R-2 > 0.999), LOQ and LOD (0.5 and 1.5 mg/L, correspondingly), recovery (95-105 %), standard deviation of repeatability (2.6 %), standard deviation of intermediate precision (3.4 %) and relative expanded uncertainty (with coverage factor k = 2 and confidence level P = 95 %) of method (7.4 %). The developed method has been applied to 23 samples of different types of alcoholic beverages (brandy, gin, rum, calvados, whiskey, bourbon, vermouth, slivovice, tsikoudia, sake, tequila, grappa, mulled wine, strong drink, grain spirit, nalewka, cocktail, krupnik, bitter and sweet tinctures, sweet, herbal and egg liquors). The absence of matrix effect associated with ethanol volume concentration and presence of non-volatile compounds in studied alcoholic beverages was proven.