Determination of vicinal diketons in beer by means of SPME method

The necessity of monitoring of the content of vicinal diketons - 2,3-butandione (diacetyl) and 2,3-pentanedione - in beer is based on the fact that the exceeding of threshold concentration of perception results in the negative influence of sensorial properties of beer, called as butter aroma. For the determination of these substances, a spectrophotometry method is used after distillation with water stream, high-efficient liquid chromatography or gas chromatography in connection with headspace technique. This work gives a new opportunity of the selective determination of diacetyl and pentanedione by means of gas chromatography. During the preparation of sample, the classic static headspace technique was replaced by solid phase microextraction (SPME). The method is easy to do, quick and in comparison with the headspace dosing device, it has significantly lower cost of acquisition. The authors dealt with finding the most suitable fiber type and conditions effecting the extraction - the effect of salt addition, various alcohol concentrations. Further to this validation characteristics of the method were measured. The new SPME method is a suitable alternative to the conventional statistic headspace technique not only from the economic point of view but with respect to efficient concentrating of analyses, it also enables the determination of free vicinal diketons without the necessity of sample temperature treatment that can influence the conversion of precursors into vicinal diketons and so influence the results of their determination. Thus, this method con be recommended for current control analyses being carried out by brewery laboratories.(In Czech, English summary only)