Chemists use infrared sensors to catch the cheats

Pouring out a measure of alcohol into a shot glass

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Can you be sure you getting the right measure?

A new portable device that uses infrared technology to identify the components of a sample could help law enforcement and regulators find adulterated alcoholic drinks or illicit products with levels of ethanol above those allowed by law for particular drinks.

Nineteenth century French chemist and physicist, Joseph Louis Gay-Lussac developed a technique for measuring the alcoholic strength by volume (per cent vol) which is, in one form or another, still in use today. The latter are based on densimetric measurements that compare the measured density of the alcohol and work out the relative proportions of the ethanol and water it contains. 

However, according to Dirk Lachenmeier and colleagues at the testing agency, Chemical and Veterinary Investigation in Karlsruhe, Germany, such devices are not precise enough for the legal measurement tolerances required by regulatory authorities. And other available techniques, including titration methods, enzymatic analysis, liquid or gas chromatographic methods etc are labour- intensive, expensive and offer no real advantage over the traditional densimetric measurement. 

In contrast, Fourier transform-infrared spectroscopy (FT-IR) provides better data and can screen samples in a couple of minutes. But, infrared spectrometers are also expensive and need to be calibrated prior to testing. According to Lachenmeier, the large investment in instrumentation means the technique is not available to smaller laboratories or small-scale manufacturers who need to keep a constant record of their products whether wine or spirits. 

Now, Lachenmeier and colleague Rolf Godelmann, working with Markus Steiner, Bob Ansay, Jurgen Weigel and Gunther Krieg of Unisensor Sensorsysteme GmbH, have developed a new infrared device that has a multiple-beam infrared sensor. By using a flow-through cell system, the sample can be fed through and automated alcohol analyses done without any complex sample preparation steps. The team has successfully tested the device with 260 different alcoholic drinks and were able to measure ethanol content to within 0.2 per cent accuracy.