How strong is that drink?

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  • Published: Jul 23, 2014
  • Author: Steve Down
  • Channels: X-ray Spectrometry / NMR Knowledge Base / MRI Spectroscopy / Infrared Spectroscopy / Proteomics / Raman / Chemometrics & Informatics / Atomic / UV/Vis Spectroscopy / Base Peak

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A simple colour test can check the ethanol content of drinks and detect counterfeit beverages containing methanol, which are a serious health hazard. It has been devised by scientists in China and is based on the colour change when a bound dye is released from a complex by the presence of an alcohol, such as methanol or ethanol. The concept is simple, if the compounds involved are not, yet they constitute a test that gives result within a few minutes.

When you mix an imidazolium-type dication with a benzothiazoline-sulphonic acid dianion, they self-assemble into a supramolecular ionic material. And, as described in Analytical Chemistry, the product is capable of encapsulating optically active compounds such as the fluorescent dye Rhodamine 6G. What is good about this construction is that it will release the dye when it is immersed in an alcoholic solution to colour the liquid in a manner that is proportional to the amount of alcohol present. The more highly concentrated the alcohol, the pinker the solution.

Rather than relying on the human eye to assess the degree of the colouration, the Chinese scientists confined the complex to a spot on a TLC plate which they immersed in the alcohol. The dye was released in a line along the plate, the length of which was related to the alcohol content of the liquid. This could be assessed visually, or the content could be determined by measuring the fluorescence signals from the lines. A linear relationship existed for alcoholic beverages of 15-40% strength.

When methanol was added to an alcoholic beverage, the lengths of the lines were increased sharply, presumably as the supramolecular material was more soluble in the solution, releasing the dye more quickly. A visual inspection would probably be sufficient to spot methanol adulteration.

This discovery presents a neat way to assess the alcoholic strength of beverages and to test for methanol in bars and clubs, since the TLC plates would be easily portable.


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