Analytical Methods Stereodifferentiation of some chiral aroma compounds in wine using solid phase microextraction and multidimensional gas chromatography Carmen Barba, Gema Flores, Marta Herraiz * Instituto de Fermentaciones Industriales, Consejo Superior de Investigaciones Científicas (CSIC), c/Juan de la Cierva 3, 28006 Madrid, Spain article info Article history: Received 29 December 2008 Received in revised form 17 February 2010 Accepted 3 May 2010 Keywords: Chiral compounds Enantiomers Multidimensional gas chromatography Solid phase microextraction Wine aroma abstract The stereodifferentiation of some chiral components of importance for the character or intensity of wine aroma was achieved with headspace solid phase microextraction and multidimensional gas chromatog- raphy coupled to mass spectrometry. Chiral evaluation of linalool and 2,3-butanediol is performed in less than 75 min (overall analysis time) using a polydimethylsiloxane/divinylbenzene fibre during the sample concentration step and permethylated b-cyclodextrin as the chiral stationary phase in the main column of the multidimensional system. Enantiomeric excesses of linalool and percentage values of 2,3-butane- diol stereoisomers were determined in three different white wines. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Delicate and balanced aroma is widely recognised as a valuable characteristic of high-class wines. Thus, wine quality evaluation demands the reliable analysis of aroma compounds, gas chroma- tography being usually the technique of choice in the separation step. However, wine aroma is a very complex mixture in which certain relevant compounds are often chromatographically over- lapped by other components which may disturb the separation and, eventually, may avoid satisfactory resolutions to be obtained. Moreover, although the influence of stereochemical aspects has been occasionally underlined in quality assurance of food and bev- erages (Ekborg-Ott & Armstrong, 1997; Luan, Mosandl, Gubesch, & Wüst, 2006; Romano et al., 2000), it is easy to realise that chiral separations and enantiomeric ratio assessments are not usually considered in the available literature when analysing wine aroma. This is probably due to the fact that enantiomeric resolutions of chiral compounds that are of importance for the character or inten- sity of wine aroma may be especially difficult as two chromato- graphic signals, for each stereochemical centre, can be observed when performing the analysis in a chiral column of adequate enantioselectivity (Schurig, 2002; Subramanian, 2001). Precisely due to the difficulty of achieving satisfactory separa- tions in complex mixtures, there is often required a substantial in- crease in the resolving power of unidimensional chromatographic techniques conventionally used. In this respect, Multidimensional Gas Chromatography (MDGC) allows a two-dimensional operation to be accomplished using two coupled columns in such a way that narrow cuts containing unresolved compounds can be selected in the precolumn and subsequently transferred to the second column, namely the main column (Bertsch, 1999; Deans, 1981; Herraiz, Reglero, Herraiz, & Loyola, 1990; Schomburg, 1995). On the other hand, the choice of the concentration procedure most suitable to enrich the sample prior to the chromatographic analysis itself is considered as one of the most critical steps when performing an analytical method. For that reason, several authors have proposed very different sample preparation approaches to analyse volatile compounds occurring in complex matrices (Bicchi, Cordero, Liberto, Sgorbini, & Rubiolo, 2008; David & Sandra, 2007; Durán, Natera, Castro, & García-Barroso, 2006; Salinas, Zalacain, Pardo, & Alonso, 2004) and, particularly, in wine aroma (Blanch, Reglero, & Herraiz, 1995,1996; Campo, Cacho, & Ferreira, 2007; Vil- lén, Señoráns, Reglero, & Herraiz, 1995; Zalacain, Marín, Alonso, & Salinas, 2007). In this respect, Headspace Solid Phase Microextraction (HS- SPME) (Pawliszyn, 1995; Zhang & Pawliszyn, 1993) has proven its versatility and ease of use for volatile analysis in complex matri- ces of quite different characteristics, also including wine aroma (de la Calle García, Magnaghi, Reichenbächer, & Danzer, 1996; Kalua & Boss, 2008; Pozo-Bayón, Pueyo, Martín-Álvarez, & Polo, 2001; Setk- ova, Risticevic, & Pawliszyn, 2007). As reported by these authors, using this technique the sample preparation step is rapidly per- formed via the extraction and concentration on the SPME fibre of volatile compounds which subsequently are thermally desorbed and then introduced into the chromatographic system. 0308-8146/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2010.05.021 * Corresponding author. Tel.: +34 91 258 75 35; fax: +34 91 564 48 53. E-mail address: ifihc23@ifi.csic.es (M. Herraiz). Food Chemistry 123 (2010) 846–851 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem