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MIR SPECTROSCOPY ANALYSIS OF CITRAL AND GERANIOL

Krzysztof Wójcicki1 and Aleksandra Zielińska2

1Poznań University of Economics and Business, Al Niepodległości 10, 61-875, Poznań, POL

2Faculty of Chemistry, Adam Mickiewicz University in Poznań, ul. Umultowska 89b, 61-614, Poznań, POL

Citral (C10H16O) is consisted of 70–85 wt.% of the essential oil of Cymbopogon citratus, commonly recognised as a lemon grass 1 2 and due to its strong lemon-like aroma can be widely used in cosmetics or as a flavor additive in food industry. Citral is a mixture of two geometric isomers: geranial (citral A; approx. 55-70 wt.%) and neral (citral B; 35-45 wt.%). On the other hand, geraniol (C10H18O), occuring mainly in rose oil, palmarosa oil or citronella oil 3 is chemically known as a terpenic alcohol: (Z)-3,7-dimethyl-2,6-octadien-1-ol that has the most significant properties in a form of geranial (citral A) 4. In this study, two of selected monoterpenes - citral and geraniol, were analysed by mid-infrared (MIR) spectroscopy to show the differences between main components and functional groups. MIR spectra were recorded on a Jasco FT/IR-4700 spectrometer using the attenuated total reflection (ATR) technique. Single-beam spectra were collected against the background of air. For each sample, the MIR spectra were recorded between 4000-500 cm-1. Measured were taken in triplicated without sample pre-preparing. As a result, the MIR spectra of two terpenes: citral and geraniol measured in the range 4000-500 cm-1 were analyzed. The spectra were offset to allow visual comparison. The obtained spectra were similar to those, which were presented by Schulz et al. 5 and Schulz and Barańska 6. For geraniol, the absorption band with maximum at 2915 cm-1, corresponds to C-H asymmetric vibrations of methylene group, was observed. This band. Moreover, the wide and flat absorption band in the range 3100-3700 cm-1 occurred, which is characteristic for OH group. For both samples the absorption bands typical for methyl salicylate (in the region 1700-750 cm-1) was also noticed. In that region, called as a “fingerprint region”, it is difficult to pick out individual bonds, but a different pattern of troughs in this part of the spectrum was shown by each of compound. For example, only for citral the intensive band (correspond to C=C vibrations) with the maximum absorption at 1671 cm-1 was observed. The results indicate that MIR spectroscopy could be used for fast identification of monoterpenes.


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