Different methods are used to test caffeine levels in beverages, including liquid chromatography, gas chromatography, and UV spectroscopy. Liquid chromatography is the most precise, while UV spectroscopy is popular. A new method uses heat-resistant antibodies to detect caffeine in drinks, but does not provide exact amounts.
There are several methods used to test the amount of caffeine in a particular beverage. The tests used depend on a number of factors, including the accuracy of the measurements. In a laboratory setting the three most common tests are liquid chromatography, gas chromatography and UV spectroscopy.
Both liquid and gas chromatography work on much the same principle, passing a mobile phase of something through a fixed bed to separate the parts. Basically, whatever you’re trying to test is being passed in a column of some sort of material. The various parts, like the caffeine in a drink, separate due to the different affinities they have for what is used as a fixed bed. The output of this process, a chromatogram, is a graph with several peaks, with each peak representing a different component. So once a test like this is done on a drink, whoever is doing it need only look at the chromatogram for the caffeine peak, to determine how much caffeine was in the overall brew.
In liquid chromatography, everything being tested will remain in liquid form as it passes through the stationary phase. Liquid chromatography can take place in a column, but it can also take place on a plane. For greater accuracy and at higher pressure, a liquid can be subjected to what is called high-performance liquid chromatography (HPLC), which is in fact what the most precise determinations of caffeine content use. In gas chromatography, the test liquid is placed in a gaseous state together with a mobile gas such as helium before passing through the stationary phase.
In UV spectroscopy, a light is passed through a liquid and how the light exits the other end helps scientists determine the caffeine content of the liquid. Different compounds have different wavelengths and these are quite accurate. By observing how the color of light passing through the liquid changes, scientists can determine in a very specific way how much of different compounds are present in the liquid. This is a fairly popular method for determining caffeine in liquids and recent advances in the field have made it even more specific.
Recently, a new method has emerged to determine whether or not a drink contains caffeine. Using heat-resistant antibodies from llamas and camels, scientists have devised a highly portable device that can be dropped into a cup of coffee or tea or any other beverage to detect the presence of caffeine. While this technique doesn’t give exact amounts, it is useful for people who are trying to avoid caffeine in their diet altogether and want to make sure that the decaf they order is actually caffeine-free.
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