The Chromatographic Analysis of Adulterated Alcohols

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Abstract

Ireland and many other countries around the world often deal with the issues regarding alcohol. These issues are based on adulteration by watering-down, addition of cheap or artificial ingredients, and the addition of harmful non-potable alcohols. Various surveys, articles and scientific studies have been developed through recent years to tackle the problems the everyday consumer has to deal with, as alcohol quality reduces and price increases. The methods of determining alcohol content are vast within the scientific community, and deciding which method is the most sensitive, accessible and affordable can be challenging. These methods include Gas Chromatography, UV/Vis Spectrophotometry, Ion Chromatography, Proton NMR and Isotope Ratio NMR.

Introduction

For many years the adulteration of alcoholic beverages has been a recurring problem in the night-scene around the country of Ireland. Adulteration refers to the addition of a substance to tamper with said-product, be it water, sugars, or drugs (CCPC, 2018). Pubs and nightclubs are commonly known to commit adulteration of spirits and other alcoholic beverages by “watering-down” their alcohol in an attempt to increase sales and also save money. Other applications of adulterated alcohol are to improve the assumed quality of the substance by adding inexpensive sources of sugar and starch, other than grapes, to improve the sweetness of wines (Lachenmeier, 2016). According to Irish law “it is illegal for a business to provide false or misleading information about a product, including its content or characteristics” (CCPC, 2018).

There have been many scandals about tampering with alcoholic beverages around the world, such as the addition of diethylene glycol to wine to heighten the sweetness of it which took place in Austria (Tagliabue, 1985). Most adulteration occurred during the early 1400-1500’s and was not detectable. During the 19th century most adulterants were undetectable (Lachenmeier, 2016) but nowadays with more laws in place it is generally more difficult to escape prosecution for committing this crime.

Many methods of identifying the composition of alcohols have been adapted over the years, including site-specific natural isotope fractionation nuclear magnetic resonance (SNIF-NMR), Gas Chromatography-Mass Spectroscopy (GC-MS), Fourier-transform infrared spectroscopy (FTIR), High Performance Liquid Chromatography (HPLC), Ultra Violet-visible spectrophotometry (UV/VIS), different Gas Chromatography detectors such as Flame Ionisation Detector, Electron Capture Detector and Thermal Conductivity Detector (GC-FID, ECD and TCD), and Ion Chromatography (Lachenmeier, 2016).

After reading several articles based on detecting alcohols it is clear to see that the methods mentioned above are the most accurate and accessible to use for different types of alcoholic beverages. The most frequently used machine is the GC-FID, which Bright (2018), Lachenmeier (2016) and Gerchman (2015) agree is the most accurate and suitable for the detection of alcoholic components, although ion chromatography is another useful method (Lachenmeier, 2003). However other authors such as Kenessov et al (2013) would argue that Solid-Phase microextraction (SPME) with GC-MS is even more efficient. Although the interpretation of the results would be expected to be straightforward, there have been incidents of the misidentification of substances such as ethyl chloride, which is used as a pain relief in sporting injuries, in place of ethanol which is a main component in alcohol, by the use of GC-FID (Tarnovski et al., 2009).

1.1-            Alcohol sales and the effects of adulterated alcohols on licensed premises

Over the last few years the issues regarding the availability of alcohol and the prices it is being sold at to an everyday consumer has been a major concern for the Irish Government. A recent survey had been carried out and appeared to conclude that fatal levels of alcohol can be purchased for as little as €10. Alcohol Action Ireland (AAI) produced a survey based on a market review and price review of alcohol, and they stated that it “demonstrates the remarkable affordability of alcohol to everyday shoppers”.  In the report it suggests that a Public Health Alcohol Bill needs to be put in place immediately to tackle issues regarding the low-cost of the strongest alcohol in various retail operators. The strongest and cheapest products were found to be cider, with beer coming next and wine, vodka and gin following up next. According to the Health Service Executive (HSE) the low-risk weekly guidelines for consuming alcohol for a healthy adult between the ages of 18 to 65 is seventeen standard drinks for men and eleven for women. A beer containing 4.3% of alcohol in a 500 ml container equals 1.7 standard drinks, whereas gin containing 37.5% of alcohol in a 700 ml container equals 21 standard drinks. Therefore, a man can reach his weekly threshold for only €8.49, and women can reach their weekly threshold for as little as €5.49 (Halpin, 2018).

A Healthy Ireland Survey was carried out in 2015 and concluded the amount of alcohol consumed by adults was at harmful levels. Four out of ten people whom consumed alcohol drank harmful levels on a monthly basis. Over a fifth of people did so on a weekly basis (HIS, 2015).

Figure 1- A pie chart representing the percentage of alcohol consumed by adults aged 15 to over 65 over the twelve months of 2014-2015. The results show alcohol consumers and non-alcohol consumers (HIS, 2015).

Consumers are purchasing more alcohol through Off-Licenses and other licensed supermarkets because it is a cheaper alternative to going out to a pub or nightclub where the case of adulterated alcohol is more common. The National Consumer Agency (NCA) published a list stating that two licensed premises were guilty of watering down their alcoholic beverages. Both premises located in County Wexford were selling their alcohol where its percentage alcohol by volume was considerably less than what was stated on the bottle. Another thirteen premises were investigated to test for adulterated alcohols due to complaints from consumers. According to the NCA chief executive Ann Fitzgerald “consumers must be provided with accurate information regarding products and not exposed to unfair or misleading commercial practices” (Shevlin, 2009).

The Irish State Laboratory carries out duties to test alcoholic beverages for their alcoholic content. The aim is to prevent counterfeit alcohols being produced and sold in Ireland as they tend to be harmful to consumers. Often adulterants such as methanol and other dangerous alcohols, that aren’t ethyl alcohol, are found which can be fatal. Methanol can also be used as a denaturant which causes the alcohol to be non-potable. A potable alcohol is one that contains pure alcohol, this includes spirits such as liquors (Cargill, 2018). Congener profiling and authenticity indicator testing is also done by the laboratory (The State Laboratory Ireland, 2014).

                   Figure 2- Image depicting empty beer bottles

 

 

 

 

1.2-            Gas chromatography and an explanation of the Flame Ionisation Detector

Gas chromatography is a method which can separate a mixture of compounds into its constituents and producing quantitative as well as qualitative results, as a gas vapour. It involves the use of gas as the mobile phase and the stationary phase is based inside the column through which the sample travels. The mixture separates when it is injected into the injection port, where it evaporates and reaches the column containing the stationary phase, and then it moves onto the detector. The mobile phase can be either hydrogen, nitrogen, argon or helium gas, depending on the type of detector. The stationary phase is present within the column. The column can be a packed or capillary column. The capillary column is the most frequently used as it is more efficient in separation. Capillary columns are made of glass or fused quartz and they also take the shape of a coil and come in different sizes (Wisniewska et al, 2015). The compounds within the sample being analysed interact with the stationary phase as it passes through the column. The longer the compound interacts with the column, the longer it takes for it to pass through. Normally the rule of “like dissolves like” is used to explain that organic substances will dissolve quickly due to the mobile phase or stationary phase containing organic compounds within them.

The detector produces the results in the form of a chromatogram. The chromatogram shows various peaks at different points on the chromatogram which correlate to the compounds that were separated during analysis (Refer to figure 4a and 4b for an example of a chromatogram). The compounds that interacted the most with the stationary phase have a longer retention time and therefore elute off later than a compound that took less time to elute off (UCLA, 2016).

Figure 3- A general schematic diagram of a GC detector. 1-carrier gas; 2-flowmeter; 3-injector; 4-column; 5-column over; 6-detector; 7-waste; 8-computer system (Wisniewska et al, 2015).

 

 

Flame Ionisation Detectors

This type of GC detector is destructive in that the sample injected is destroyed. The sample being analysed goes through a column and is partially combusted within a hydrogen flame which forms different free radicals such as hydrogen, oxygen, and hydroxide (HO and OH). If carbon is present, then it creates an aldehyde (CHO). The ions are gathered on the collection electrode and are counted. The mobile phase used in this type of detector is normally helium. The detector can range in sensitivity i.e. 0.1g to 10g. The temperature at which the detector would usually operate is between 250ºC and 300ºC but can also go up to as high as 400ºC to 450ºC. The reason behind using such a high temperature it so there will be no condensation formed during combustion. (Wisniewska et al, 2015).

Figure 4- A schematic diagram of a GC-FID. 1-capillary column; 2-air inlet; 3-hydrogen inlet; 4-polarized electrode; 5-burner; 6-hydrogen flame; 7 and 8- collector electrode; 9-gas outlet (Wisniewska et al, 2015).

1.3-            Various ways to prepare a sample prior to chromatographic analysis

According to Wisniewska et al (2015) the way in which a sample is prepared before it is analysed using chromatographic techniques depends on the sample being investigated. Methods that are most commonly used are Solid-Phase microextraction (SPME), Liquid-liquid extraction (LLE) and Solid-Phase extraction (SPE).

Solid-Phase Microextraction

Small amounts of the sample adsorb onto a thin layer of stationary phase which coats the glass or quartz fibre. The fibre is within a tube which must contain no rust, and this is found in the syringe. Mass exchange occurs during enrichment and adsorbed compounds are released to prevent clogging of the tube, which can occur due to suspension in the sample. Immersing the exposed fibre into the liquid or placing the fibre into the head space above the sample will lead to enrichment. Organic compounds are separated between the stationary phase and the matrix. Afterwards the fibre gets retracted inside of the needle, which is then put into the injector and the fibre is exposed. The use of a high temperature changes the organic compounds in the stationary phase to desorb into a gas which can be forced onto the column by the carrier gas. This technique of sample preparation has both advantages and disadvantages when it comes to preparing a sample. Some advantages include; the use of mobile or portable equipment, it is a simple technique to carry out, it is low in cost, and it takes a short time to complete the preparation before analysis. One of the disadvantages includes the degradation of the stationary phase during desorption under high temperatures.

Liquid-Liquid Extraction

This technique is well known and used for preparing samples. The extraction can only be performed with two phases of immiscible liquids. The extraction involves the addition of a solvent to the mixture that contains the component to be extracted for analysis. The highest concentration of the component being extracted needs to be secured. This is done so by adding a suitable extractant. The extractant mixture needs to contain the lowest concentration, and an equilibrium is reached between the two. The two phases are separated mechanically, and the extraction is repeated numerous times. The extracts are washed with the dissolvent and then they are dried using a drying agent. The main advantages of this method are the simplicity of the technique and the low-cost equipment. The disadvantages are the high cost of the solvents as well as the loss of the obtained material.

Solid-Phase Extraction

Analytes are transferred from the sample to the solid phase. It uses a water/solid partition for the analysed organic compounds. There are two ways in which the technique can be done. One method involves the compounds passing through a column whilst the substances that remain are adsorbed by the column packing. The second method involves the compound being adsorbed by the column packing whilst the other substances are passed out of the column. This is used when the concentration of the analyte in the sample is low. The advantages of SPE are that it requires less solvent than LLE and it is also inexpensive to do. The disadvantages include the length of time it takes to carry out the extraction and the clogging of the column bed due to suspension in the sample.

Upon reading and analysing the various techniques explained by Wisniewska et al, it would be suggested that the SPE method is the most useful way to prepare a liquid-based sample (2015). Another article also found during experimentation that SPE gave higher recovery for alcohols in rose aromatic water in comparison to liquid-liquid extraction and solid-phase microextraction (Canbay, 2017).

For most GC-FID methods, the above procedures do not need to be carried out. The samples, in this instance being alcohol including an internal standard of propanol, can be injected directly into the detector. This is due to the method being destructive of the sample being analysed.

1.4-            Use of ion chromatography vs. gas chromatography for analysing vodka and rum samples

There are a wide variety of brand-name spirits available to the everyday consumer which tend to be expensive, therefore it can be desirable to produce adulterated versions of these products or to even relabel cheaper versions. The most common premises to come across these alcoholic beverages would be the nightclubs and pubs who sell their spirits very cheaply. In Ireland it is easiest to dilute alcohol with water to reduce the strength, therefore causing increases in sales due to the lesser effect the alcohol has on the consumer. It can be easily detected if an alcohol sample has been tampered with, as the content will be much lower than the original product.

One method used for the authentication of vodka, rum and brandy is ion chromatography. A study carried out by Lachenmeier et al (2003) used ion chromatography to determine chloride, nitrate and sulphate for characterising spirits such as vodka and white rum. In this study it was stated that gas chromatography is normally used to identify substances that are volatile. However, a new and improved method of using ion chromatography can determine the ionic content of domestic water and brand-specific spirit water used for distillation which show different compositions. It was concluded that ion chromatography is an easy way to determine the ionic composition as it requires very little sample and very little sample preparation.

Figure 5a- Ion chromatogram of vodka samples with (A) Suspicious vodka sold as Smirnoff and (B) Authentic Smirnoff (Lachenmeier et al, 2003)

Figure 5b- Ion chromatogram of rum samples with (A) Suspicious rum sold as Bacardi and (B) Authentic Bacardi (Lachenmeier et al, 2003)

High sensitivity, reproducibility and selectivity are shown during the analysis which is a must have to produce accurate results. The study also concluded that a GC analysis was carried out for the vodka and run samples which only showed acetaldehyde and isoamyl alcohol present in the vodka samples. Originally in another study carried out by one of the same authors, Lachenmeier (2016) had claimed that GC was a suitable method for the same analysis, which would appear contradictory but perhaps giving the difference of 2003-2016 there have been advancements made regarding the accuracy and expandability of the GC method. Upon further reading it was discovered that there was a large difference in chloride, nitrate and sulphate levels using GC methods and therefore it was an acceptable way to determine the purity of the alcohol samples. It also concluded that the expansion of samples to other spirits such as whiskey and brandy could also be determined using ion chromatography by extensive sample preparation.

 

Table 1a- Gas chromatography results of suspicious vodka sample sold as Smirnoff and reference Smirnoff and German vodka samples. ND = Not Detected (Lachenmeier et al, 2003).

 

Table 1b- Gas chromatography results of suspicious white rum samples sold as Bacardi and reference Bacardi and authentic German rum samples. ND = Not Detected (Lachenmeier et al, 2003).

1.5-            The use of Fluorescence Spectroscopy to determine adulterated alcoholic beverages

A study carried out by De la Rosa Vazquez et al (2015), examined the use of fluorescence by UV light to determine adulterated tequila from genuine tequila. A fluorescence spectrum was produced showing four excitation wavelengths at 255, 330, 365 and 405nm for the genuine tequila, ethanol, ethanol-water mixtures and methanol. The results gathered have been given in figure 6 below. The distilled water and the ethanol gave very little absorption. The methanol showed a small decrease in transmittance with the wavelength shortening up to 330nm which later gave an absorption at 250nm. The fake tequila was the only sample to show an incomparable dependence of the wavelength.

Figure 6- A Fluorescence spectroscopy spectrum of distilled water (DW), ethanol (ET), methanol (ME), aged tequila (AT), rested tequila (RT), mixed tequila (MT), silver tequila (ST), and fake tequila (FT), at 255nm, 330 nm, 365nm and 405nm (De la Rosa Vaquez et al, 2015).

It had been concluded from the results that the fluorescence excited at 255nm could be used to show the adulterated tequila from the original tequila. The method could be improved by the measurement of spectral transmittance in the 255 to 405nm wavelength interval. Overall the use of fluorescence spectroscopy is a very practical method in determining the adulteration of alcoholic beverages, specifically tequila.

1.6-            Wine fraudulence and the use of SNIF-NMR and Proton NMR to detect it

The main components of wine include acid such as malic acid and lactic acid, alcohol such as ethanol, sugars, tannin and water (Spirits wine cellar, 2016). The most common ways in which wine has been adulterated is through the addition of sugars and watering down the samples, but nevertheless seriously dangerous additions have been made, such as lead salts which clarified and sweetened the wines. This type of practice occurred in France during the 19th century, but as analytical chemistry techniques became more advanced over the years, the adulterations became more refined. It is thought that at least 10% of wines produced in Europe are of lesser quality than what is being indicated on the label, but the taste would not be any different in comparison to high quality wines. Geographical origins are a popular concern in the production of wine and the most common way to establish the origin of wine samples was through stable isotope ratios, due to the isotope ratios varying depending on the country’s climate. Site-specific natural isotope fractionization nuclear magnetic resonance (SNIF-NMR) could then be used to determine the distribution of deuterium in ethanol along with the isotope ratio of water, ethanol and glycerol (Lachenmeier, 2016).

Proton NMR has been developed to detect wine samples because of its high sensitivity and its ability to predict the variety of the grapes used in the wine. After a study was carried out by Godelmann et al, a sample of over 600 wines produced in Germany were detected for different grapes such as Pinot Noir, Müller-Thurgau, Riesling and Gewürztraminer which were easily distinguished with 95% accurate predictions (2013).

Figure 7- A proton NMR spectrum showing the separation of peaks depending on the type of acid present. There is a presence of tartaric acid, glycerol, MeOH, succinic acid, acetic acid, lactic acid, malic acid, glucose, GABA, proline and sorbic acid (A-Lachenmeier, 2016) (B-Godelmann et al, 2013).

The method of SNIF-NMR is also useful for analysing beer samples for the distribution of deuterium in ethanol. Although there is a lack of literature for analysing and authenticating beer in comparison to wine, it can be of interest to test it to differentiate certain types of beer or to determine different malt types used in the beer. Other methods apart from SNIF-NMR can be used such as FTIR and Proton NMR. Since beer adulteration is not harmful to a consumer, the development of analysing it has not taken place in recent years and it may remain that way due to the lesser importance of it compared to the authenticity of wines and spirits (Lachenmeier, 2016).

Conclusion

After reading and reviewing various studies on methods for analysing alcohols for adulterants it can be said that different types of alcohol i.e. beers, wines and spirits (such as vodka, rum, tequila, brandy and whiskey), can be analysed using different machines and techniques. Various sample preparation techniques can also be used, and they all have their own advantages and disadvantages.

The techniques that both wine and beer have in common is the SNIF-NMR. It can detect geographical origins and varieties of grapes which was discovered by Godelmann et al, (2013) and Lachenmeier (2016). Beer can be tested using other methods such as FTIR and Proton NMR to distinguish its type and if there may have been brand fraud, but they have not been applied over a large range due to lack of risk factors to humans when looking at adulterated beer consumption.

Vodka and rum can be easily detected using GC-FID or ion chromatography. Compounds such as ethanol, acetaldehyde, chloride, nitrate, n-propanol and iso-butanol were detected using gas chromatography. GC has developed over a period of time, to become more accurate and sensitive, and therefore more acceptable to use for determining alcohol purity. Regarding spirits such as brandy and whiskey, it may be more desirable to use ion chromatography due to its sensitivity and the extensive sample preparation that may not be available with gas chromatography (A-Lachenmeier, 2016), (B-Lachenmeier et al, 2003). Gas chromatography, however, is much more accessible and common for everyday analysis and would be perfectly acceptable to use for analysing the majority of alcohol samples.

Tequila was found to be best analysed using fluorescence spectroscopy. Adulterated tequila could be distinguished from genuine tequila by comparing the wavelengths at which each component in the tequila absorbed at. Although it is a suitable method for tequila, it may also be possible to detect other types of alcoholic beverages by fluorescence spectroscopy (De la Rosa Vazquez et al, 2015).

Sample preparation through SPME, LLE and SPE gave many similar advantages and disadvantages. The advantages included the low cost of the equipment required and the simplicity of the preparation. The major disadvantage concluded was the loss of material. Upon interpretation the SPE method for sample preparation was the best because it required very little solvent compared to LLE and it was inexpensive to carry out. It also gave a higher alcohol recovery in comparison to LLE and SPME in rose-aromatic water (Canbay, 2017). The main disadvantage in relation to SPE is the length of time the preparation takes to complete (Wisniewska et al, 2015).

Method Pros Cons
SNIF-NMR -Can detect geographical origin of samples -Can take time to carry out investigations

-Has not been developed to detect any other types of alcohol

FTIR -Can detect different types of alcohol, such as beer, to detect any fraud -Must be compared to known fingerprint regions

-May require further analysis such as Proton NMR

GC-FID -Can easily detect fraudulent vodka and rum samples

-Can be accessible for everyday use

-Requires little or no sample preparation

-Inexpensive to run

-Can be subject to a limited range in sample analysis

-Requires development to analyse samples such as whiskey and brandy

Fluorescence Spectroscopy -Analysis of results is easily done by comparing wavelengths -Research has only found use in analysing genuine tequila samples against adulterated tequila

Table 2- Summary of methods of analysing alcohol samples, giving both pros and cons of each method

Table 3- Summary of sample preparation of GC samples and the pros and cons of each method

Method Pros Cons
SPME Inexpensive to prepare

-Portable equipment

-Easy method to follow

-Does not require a lot of time

Stationary phase degrades due to high temperatures
LLE Equipment used is inexpensive

-It method is easy to follow

Solvents used are expensive

There can be a loss of obtained material

SPE It requires less solvent than LLE

-It is inexpensive to carry out

-There is a higher recovery of samples

The extraction can be time consuming

-The column can become clogged due to suspension in the sample

 

References

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