Determination of 3 Furfural Compounds in Coffee Beverages by Gas Chromatography-Mass Spectrometry with Ethanol Solution Extraction and Liquid-Liquid Extraction Displacement

A method for determination of furfural, 5-methylfurfural, and 5-hydroxymethylfurfural in coffee beans (powder), pure instant coffee, all-in-one instant coffee, and coffee-flavored drinks was proposed. After the sample was crushed, the 50% (volume fraction) ethanol solution was added as an extraction solvent, and the 10% (mass fraction) sodium carbonate solution was added as an alkaline treatment agent. The mixture was extracted by ultrosound at 40 ℃. Three furfural compounds in the extract were replaced by liquid-liquid extraction using acetonitrile, to reduce the damage of the aqueous extract to liquid chromatographic column and the effect of impurities on the determination. A mixed internal standard solution containing both ¹³C₆-5-hydroxymethylfurfural and furfural-d₄ at a mass concentration of 10.0 mg·L^-1 was added, and the solution was mixed well by vortex and centrifuged. The mixed solution was placed into a QuEChERS purification tube containing 100 mg of C₁₈ bulk filler, 50 mg of DSC-SCX strong cation exchange solid-phase extraction bulk filler, and 200 mg of anhydrous magnesium sulfate. The mixture was mixed well by vortex, and centrifuged, and the supernatant was determined by gas chromatography-mass spectrometry. Three furfural compounds in the obove supernatant were separated on an HP-INNOWAX elastic quartz capillary chromatography column under programmed temperature conditions, ionized by electron impact ion source, detected by selected ion monitoring mode, and quantitatively detected by the internal standard method. It was shown that linear relationships between values of the mass concentration ratios and quantitative ion peak area ratios of 3 furfural compounds to their corresponding internal standards were kept in the range of 0.050-9.92 mg·L^-1, with detection limits of 0.002, 0.002, 0.003 mg·kg⁻¹ for furfural, 5-methylfurfural, and 5-hydroxymethylfurfural, respectively. Coffee bean powder samples with low detection amounts of 3 furfural compounds were used as matrices for 2 concentration levels of spiked recovery tests, giving recoveries in the range of 94.0%-107% and RSDs (n=6) of the determined values in the range of 0.70%-2.2%. The proposed method was used for the analysis of 32 actual samples, 3 furfural compounds were detected, and average detection amounts of 5-hydroxymethylfurfural in pure instant coffee samples were highest.