Influence of the Scanning Temperature on the Classification of Whisky Samples Analysed by UV-VIS Spectroscopy  
[PERSON]  
[PERSON] and [PERSON]  
1 School of Science, RMIT University, GPO Box 2476, Melbourne 3001, Australia 1  
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distinct UV fingerprints, while the most abundant sample components, such as water, alcohol, organic acids, and sugars, have no absorbance in the UV wavelength region (200-600 nm) [2; 7; 15; 17]. Recently, analytical methods based in UV-VIS spectroscopy have been reported as having a great potential to target issues related with brand authentication and traceability in a diverse group of distilled spirits, such as whisky, brandy, rum, and other flavoured spirits [7]. In addition, UV-VIS spectroscopy has also shown its potential in the authentication of beer, wine, and other non-alcoholic beverages (although sample filtration and degassing may be required prior to spectral analysis) [2; 15; 17]. Nowadays, developments in data handling and mining techniques have provided new opportunities to develop and enhance the analysis of the spectra (e.g., the use of derivatives) [3; 17; 18; 19]. UV-VIS spectral analysis can provide information on covalently unsaturated compounds with electronic transition energy differences equivalent to the energy of the UV-VIS light that absorbs at specific wavelengths [20; 21]. These compounds are known as chromophores and are responsible for the colour of the sample [20; 21]. Covalently saturated groups usually do not absorb in the UV-VIS region of the electromagnetic spectrum but can influence or alter the absorption of some chromophore groups [2; 3; 20; 21]. It is well known that when UV-VIS radiation interacts with chromophores, electrons in the ground state jump to an excited state, known as the electron-excitation state. Meanwhile, other chromophore molecules can act as electron-donating entities with the ability to affect the colour of the chromophores, but they do not change colour themselves [2; 3; 20; 21]. On the other hand, water and other organic compounds (e.g., alcohol) are mostly transparent and do not absorb in the UV-VIS region [2; 3; 20; 21].  
It has been reported that the spectrum of alcohols is very sensitive to scanning temperature due to the self-associated forms of the alcohols dissociated into small oligomers, dimmers, and monomers as a function of temperature [22]. For example, it has been demonstrated that temperature changes affect the vibration intensity of molecular bonds in the near infrared (NIR) region, thus the spectrum changes according to the temperature variation [22]. Although extensive research has been done on the effect of temperature on the NIR spectra of alcoholic beverages, no information is available when UV-VIS spectroscopy is used to analyse alcoholic beverages [22; 23; 24; 25; 26]. It has been reported that increasing temperature dilates solvents, thus to measure concentration accurately requires a correction factor for the coefficient of thermal expansion. However, volume expansion may impact absorbance less than the effect of temperature on hydration of the chromophore compounds. Therefore, the definition of the optimal temperature and its effects (increasing or variations of temperature) during analysis are of importance to develop a protocol to analyse alcoholic beverages using UV-VIS spectroscopy [22].  
Although few reports have been published on the use of spectroscopy combined with chemometric methods to classify and authenticate alcoholic beverages such as whisky [2; 3; 7; 27], no reports were found in relation to the effect of temperature during spectra collection and its consequences on the classification performance. The objective of this study was to evaluate the effect of increasing temperature on both the UV-VIS spectra of whisky and on the classification results of the samples according to country of origin.