Extraction from Wine and Grape Juice

Liquid-liquid extraction can be performed using as an internal standard 2-undecanone (150 pL of a 100-mg/L ethanolic solution added to 1.5 L of sample). The sample is extracted three times with 60,40, and 40 ml. of pentane for 10 min with stirring. The extracts are collected together and the resulting solution is concentrated to 10 mL at 4°C under vacuum, then concentrated to 500 pL, and purified on silica gel (70-230 mesh, 60A), activated at 120 °C. The wine extract is then passed through the silica column (100 x 10 mm) and four 40-mL fractions are recovered using pentane (I), pentane/dichloromethane 

80 20 (II), pentane/dichloromethane 60 40 (III), and pentane/dichlo-romethane 50 50 (IV). Geosmin is recovered in fraction II. This solution is concentrated to 500 pL under a nitrogen flow before GC/MS analysis (Darriet et al., 2000). 

HS-SPME has been used for analysis of geosmin in wine 5 mL of sample is transferred in a 20-mL vial and saturated with 3 g of NaCl. The solution is diluted 1 1 by volume with water acidified to pH 3. Sampling is carried out by a PD MS 100-pm fiber at 40 °C while keeping the solution stirred for 30min. Desorpition of fiber is performed in the GC injector port at 260 °C (Dumoulin and Riboulet, 2004). 

Usually a PEG fused silica capillary column (e.g., 50m x 0.25 mm i.d., 0.25-pm film thickness) is used with the following oven temperature program 45 °C isotherm for lmin, 3°C/min to 230 °C, isotherm for 10min. An example of a GC chromatogram for a Cabernet Sauvignon wine analysis is shown in Fig. 8.10. The GC/MS-EI (70 eV) mass spectrum of geosmin is reported in Fig. 8.11 (Darriet et al.,2000). 

Mass spectrum ions used for identification of geosmin are at m/z 111, 168, and 182. Quantification is performed on the ion at m/z 112 recorded in SIM mode. For internal standard 2-undecanone, the signal recorded is 

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