GC-MS Determination of Volatile Compounds in Wine Using Needle Concentrator INCAT
Abstract
There are several methods for determining of volatile organic compounds in wine. All these sample preparation methods present several disadvantages, such as excessive cost, volume of sample and time, the possible generation of artefacts, etc. Previously developed simple method of solventless extraction of volatile organic compounds from liquid samples has been applied to wines samples. Inside needle capillary adsorption trap device (INCAT) with Carboxen 1000 as a sorbent material and wet alumina as a source of desorptive water vapour flow in a closed GC analytical system is presented. In relations to other extraction techniques used in wine analysis like liquid-liquid and solid-phase extraction, purge-andtrap, and solid-phase microextraction, the INCAT technique offers some advantages because it does not require solvent or any sample treatment, is fast, inexpensive, requires low sample volumes. The analytical characteristics of developed device and of compared purge-and-trap device for analysed samples are similar; the limits of detection as well as quantification are approx. 1 ng/l. The main advantage of INCAT device lies mainly in substantially lower price of analysis and the possibility of sampling directly in the field.
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Introduction
Wines contain over 800 different volatile organic compounds (VOCs) belonging to different chemical families such as alcohols, ketones, aldehydes, esters, lactones, etc. [1-3]. Among major compounds beside ethanol belong ethyl acetate and higher alcohols. Ethyl acetate is the most abundant ester in wines and is produced by the yeast during the alcoholic fermentation and by the acetic bacteria metabolism. High amounts of ethyl acetate can be considered to be a symptom of wine spoil. It is known that the content in higher alcohols is a factor conditioning wine quality. Amounts higher than 400 – 500 mg/l imply defects in the aroma [1]. Wine quality is significantly influenced by flavor compounds from different chemical families in different concentrations, too. Such compounds come from grapes, fermentation processes and wine ageing. However, both qualitatively and quantitatively, fermentation compounds are the main group, especially esters, which play an important role in white wine aroma [2, 4]. The main technique to analyze these wine components is gas chromatography (GC). The quantification of minor compounds needs a prior concentration step, while major compounds can be analyzed by direct injection of wine sample.
Classical analytical methods used for gas chromatographic analysis of wine volatile compounds such as liquid-liquid extraction [5], purge and trap [6], solid-phase extraction [7, 8], etc., have at least one of the following disadvantages: taking a long time, laboriousness, possibility of contamination or loss, artifact formation, use of environmentally hazardous solvents, difficulties in automation, etc. [4]. Over the last two decades solid-phase microextraction (SPME) has become a powerful technique, commonly employed for the analysis of aroma compounds in wine [3, 9-16]. SPME presents many advantages over traditional analytical methods by combining sampling, preconcentration, and the transfer of the analytes into a standard gas chromatograph. The sensitivity of SPME coatings, such as polydimethylsiloxane and divinylbenzene (PDMS/DVB) and Carboxen/PDMS, was reported to be very high for extracting VOCs. However, competitive adsorption and displacement effects make mass calibration and quantification particularly challenging.
Conclusion
A simple method of solventless extraction of volatile organic compounds from liquid samples has been applied to wine samples. In relation to other extraction techniques used in wine analysis the INCAT offers many advantages because it does not require solvent or any sample treatment. The main advantages of this method lies particularly in the possibility of sampling directly in the field, and very short sampling time up to two minutes.