Quantitative Evaluation of Methanol Content in Beverages Based on Raman Spectral Data

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1 Quantitative Evaluation of Methanol Content in Beverages Based on Raman Spectral Data HANA VASKOVA Tomas Bata University in Zlin Nad Stranemi 45, , Zlin CZECH REPUBLIC Abstract: - The topic of the contribution arises out of the actual situation in the Czech Republic, where the methanol affair was unleashed in autumn 0. A large amount of harmful toxic alcohol containing methanol in quantities many times over legal limit has been illegally distributed. This event led up to serious problems with poisoned people and the losses in lives. However, after-effects may occur in future. For this reason an innovative method for quantitative evaluating the methanol content in drinks has been developed. A novel approach lies in using Raman spectroscopic data which gives unique information about the structure of material. Raman spectroscopy provides a rapid, nondestructive and noncontact analysis that can be performed through the glass. These properties bring benefits over the typically used chromatographic techniques. The method is based on diverse Raman spectra for methanol and ethanol and their mathematical processing. Essential information comes from the calibration data. The detection limit of the method lies below the permitted and even safe amount of methanol in the beverages. Key-Words: - Evaluation, methanol, ethanol, Raman spectroscopy, fitting, intoxication, alcoholic drinks Introduction Alcoholic beverages are popular in many countries and often consumed. Due to its effects on the human organism the popularity is linked to the content of ethanol. Several health problems have been observed in recent years in Estonia, Norway, Turkey, Brazil, China, India []. Now another country Czech Republic solves problems with harmful alcohol, poisoned people and the losses in lives. According to the Ministry of Health 7 people were poisoned, forty-two of them died after consuming dangerous alcohol since last autumn. Problem is that not all the dangerous beverages are already captured. This affair can last to the future and effects may occur even after several years, when someone gets to the defective alcohol. Workers of regional health authorities and Health Station in Prague made through the autumn 0 a total of 7,34 controls, analyzed 03 samples of beverages, 6 samples did not regard the content of methanol. [] This is a great risk of consumers of alcoholic beverages from unknown sources. The ingestion of drinks with the nonqualified raw materials containing high levels of methanol can cause serious health difficulties metabolic problems, blindness, permanent neurological damage or even death. Methanol itself can be harmless, but in the organism is transformed into highly toxic formic acid. The effects of intoxication are fast, that is why it is important to recognize the methanol intoxication in time. The lethal oral dosis for human is from 30 to 00 ml of methanol [3]. To taste, smell or appearance methanol cannot be recognized from ethanol. Common method for laboratory proving of methanol content is gas chromatography. Problem Formulation Interest in the problematic of detection methanol in beverages has serious reasons that are connected to human health and lives. In the situation when a large quantity of harmful toxic alcohol containing excess of methanol is spread among people, it is advantageous to have a reliable and rapid method for methanol identification and quantification. These features provide Raman spectroscopy a modern analytical method for identification of different types of substances and materials. Raman spectroscopy was studied and after experimental data acquisition was used for developing a quantitative determining of methanol in alcoholic beverages. ISBN:

2 3 Theory Methanol CH 3 OH is the simplest aliphatic alcohol. It is a colorless liquid freely miscible with water and other alcohols, is transparent and volatile and highly flammable. Its confusion with ethanol CH 3 CH OH, the alcohol complex with similar properties can have fatal consequences. It cannot be clearly distinguished by smell or taste. In distillates significantly prevails ethanol, which is primarily metabolized. Several thousand methanol poisoning happen every year all around the world and many of them ending in death [4, 5]. 3.. Limits of methanol According to Czech legislation the permitted and safe limit for methanol in spirits is to grams per liter of pure ethanol. From known concentrations of these substances for the purposes of the experimental part of this research the value can be recalculated. The limit concentration is 0.756% of methanol in ethanol. 3.. Raman spectroscopy Raman spectroscopy is an analytical tool that becomes a valuable part of laboratories around the world in recent years. In principle, Raman spectroscopy as a vibrational spectroscopic method has the potential to answer a number of questions related to chemical details of molecular structure what makes this technique definitely proper for material identification. Raman spectroscopy provides very specific chemical fingerprint of every single chemical substance in the form of the Raman spectrum. Raman effect, the fundamental principle of Raman spectroscopy is known since thirties of the 0th century. The effect remained for a long time only on a theoretical level and practically was marginalized because of low sensitivity and difficulties with overcoming fluorescence phenomena. However, renaissance of Raman spectroscopy is coming even in the last decade hand in hand with technical advancements and latest developments in the field of new extremely sensitive detection devices, efficient filters for filtering Raman scattered light from the Rayleigh scattering, and also innovative laser technology designs. As is known, molecules have an ability to absorb or emit photons an electromagnetic radiation with specific energy and by this way change their own energy. Raman spectroscopy is based on the characteristic vibrations of molecules of investigated sample caused by monochromatic light of laser. After irradiation of the sample by monochromatic light we can observe the scattered light with a predominant representation of laser wavelength, but there are also other slightly changed wavelengths characteristic for the substance. Let follow the analogy with human fingerprints every single human being on Earth have different set of fingerprints. Every single chemical substance has its own specific fingerprint its unique Raman spectrum the key for the identification. Diagram of the measurement using Raman spectroscopy is shown in Fig.. Fig. The sample is irradiated with laser, molecule vibrates, filter eliminates intense Rayleigh scattering, the grating disperses the light onto a detector to generate a spectrum, which gives the information about molecule bonding and provides a chemical fingerprint utilizable for identification. Raman spectroscopy brings advantages of nondestructiveness, non-contactless of the measuring. It is not necessary to come into direct contact with hazardous toxic substances. Analyses are rapid Raman spectrum can be acquired within seconds. Another great benefit especially for application in beverages is the ability to measure through transparent packaging materials - glass, plastic, what is safe, convenient and prompt Fitting the spectral data Coming out of the quantum theory, transitions between energy levels in molecules after absorbing or emitting energy and related lifetimes it is proper to use for fitting Raman spectral data different functions. Gaussian () is usually used for solids, Lorentzian () for gasses. ISBN:

3 ( x µ ) f ( x) = e σ () σ π L( x) = π ( x x Γ 0 ) + ( Γ) () Where x 0 represent the centre, parameter Γ specifies the width. In the case of methanol a liquid a combination of these functions the Gaussian- Lorentzian profile is an appropriate solution. Spectral line shapes has features of both Gaussian and Lorentzian character. The Gaussian-Lorentzian is represented A G + ( A) L ( 3) Where A is a variable parameter in the fit being the fraction of Gaussian character (0 A ). 4 Experimental part To verify the applicability of Raman spectroscopy to measure the methanol content in alcoholic beverages it was necessary to prepare suitable samples. Then to find appropriate measurement parameters, measure the samples, process the results and create calibration curves. On the basis of calibration curves was created a procedure for experimental detection of the dangerous methanol in alcoholic beverages. excitation wavelength 54nm and maximum output power of 0 mw and 785 nm and NIR diode laser with maximum output power 300mW. Both were tested but more precise results were obtained using NIR laser. A Leica DM 500 confocal microscope with the resolution up to μm was coupled to the Raman spectrometer. All measurement were collected at 5x - 0x magnification, with 0s exposure time and 0 accumulations. The samples were firstly scanned in range 00 to 300 cm - with cm - spectral resolution. After determining the principle peaks the spectral range was reduced approximately to the area cm -. 5 Results Raman spectra of pure methanol and ethanol are displayed in Fig.. Main attention was paid to two dominant peaks: 035 cm - for methanol (C O stretching) and 88 cm - for ethanol (C C stretching). All sample mixtures were analyzed under the same conditions. 4.. Mixtures of methanol and ethanol Pure methanol and pure 00%ethanol were used for the set of mixtures. Fifteen mixtures were prepared in concentration range 0.05% to 50% solution of methanol in ethanol. Concentrations close to the limit value of the relevant legislation were chosen with little difference. Mixtures were analyzed both directly under the Raman microscope and in glass vials. Advantage of vials consists in preventing evaporation of the two components, which is relatively fast. Thus the concentration difference between the actual and prepared concentration emerging already in short period of several seconds was reduced. 4. Raman spectroscopy InVia Basis Raman microscope from Renishaw was used for recording Raman spectra methanol and ethanol mixtures. The Raman instrument uses two lasers as light sources: argon ion laser with the Fig. Raman spectra of pure methanol and ethanol The obtained spectra are shown in Fig.3. Baseline corrections were applied on acquired spectra. The spectra were subjected to normalization according the intensity of corresponding ethanol peak at 88 cm -. Spectrum of normalized ethanol was subtracted from all the resulting spectra what allowed focusing on methanol peak at 035 cm -. Subtracted data are shown in Fig 4. Data for calibration curve were acquired by fitting the methanol peak at 035 cm - using Gaussian- Lorentzian profile. Obtained methanol peak intensities were plotted against the concentration of methanol in samples resulting in a linear ISBN:

4 Fig. 5 Calibration curve of methanol Fig. 3 Raman spectra of prepared mixtures of methanol and ethanol dependence with R value 0,990, the calibration curve of methanol. The detection limit for the method was 0,5% of methanol in ethanol. Lower concentrations were not detected on Raman spectra. subtraction of normalized ethanol spectrum is performed and methanol peak intensity is obtained from the resulting spectrum by fitting. Then it is evaluated according the calibration curve for methanol. The process of methanol determination was verified on ten mixtures with known concentrations, the standard deviation was at average 0.%. The method was meanwhile applied on alcoholic beverages mainly form most trusted sources or distilled beverages, detrimental one not yet been revealed. Fig. 4 Methanol peak of mixtures after ethanol subtraction 5.. Alcoholic beverages The process of measuring the methanol content in alcoholic beverages is based on the obtained data and dependences. Sample of alcoholic beverage is analyzed due Raman microscope, baseline correction is applied on the spectrum, the 6 Conclusion An innovative method of measuring methanol in alcoholic beverages was created in connection with the recent methanol affair in the Czech Republic in autumn 0. The method utilizes Raman spectroscopy as a tool for rapid, nondestructive and noncontact analysis that can be performed through the glass bottles since the glass does not affect the Raman spectrum of beverage. With knowledge of the calibration of methanol and implementation of all the steps with the measured spectra there can be quite accurately determine whether the alcoholic beverage is defective and health-threatening or not. Acknowledgments: This work is supported by the Ministry of Education, Youth and Sports of the Czech Republic, by European Regional Development Fund under the project CEBIA-Tech No. CZ..05/..00/ The work is also supported by Internal Grant Agency of Tomas Bata University in Zlin under the project No. IGA/FAI/03/00. ISBN:

5 References: [] Yayci, N., Agritmis, H., Turla A., Koc, S. Author, Fatalities due to methyl alcohol intoxication in Turkey; an 8 - year study, Forensic Science International. Vol.3, 003, pp [] Ministerstvo zdravotniství České republiky [online] [3] M.J.C. Pontes, S.R.B. Santos, M.C.U. Araújo, L.F. Almeida, R.A.C. Lima, E.N. Gaião, U.T.C.P. Souto. Classification of distilled alcoholic beverages and verification of adulteration by near infrared spectrometry. Food Research International. Vol. 39. Is., 006. Pp [4] Široký, M. Otrava methanolem. Prevence úrazů, otrav a násilí [5] Davis, L. E., Hudson, D., Benson, B. E., Jones Easom, L. A., Coleman, J. K.: Methanol poisoning exposures in the United States: Journal of Toxicology - clinical Toxicology. Vol. 40, 00. pp ISBN: