What is the standard industrial method for measuring caffeine content in food and drinks?

There are a lot of questions here looking for simple methods to measure caffeine content (or extract it), including one of mine here and on the [*Coffee* site](https://coffee.stackexchange.com/tour):


* [Home science optical absorption test for approximate caffeine quantity in coffee?](https://chemistry.stackexchange.com/q/70793/16035)
* [Are there any ways that coffee consumers can measure the caffeine content of what they are drinking by themselves?](https://coffee.stackexchange.com/q/6073/9096)


But here I'd like to ask something different:


**Question:** Is there a standard industrial method for measuring caffeine content in food and drinks?


For example, if there were government requirements to post the amount of caffeine in a product there may be some standard way that government advised that it be done (i.e., "this is the way we're going to do it to verify what you report."). While I don't know of any such requirements, that doesn't mean there aren't any.




The answer is fortunately rather simple. Use a C18 reversed phase column and a UV detector in an HPLC system. One would make a calibration curve by injecting various concentrations into the column. Now, if an unknown sample of a drink is injected, and one sees a peak at the same retention time in the sample chromatogram, you know it is caffeine. By interpolating the area, we know its concentration. When an HPLC method is developed, it is ensured that no other component elutes at the same time. This is achieved by using gradients of mobile phase composition.


If there is a *legal* issue and one has to provide a 100% foolproof test, then one has to use a mass spectrometer along with a UV detector to confirm the identity of the peak at various locations, i.e., one ensures that the peak is pure.


See the examples in Agilent's note "Determination of Caffeine in Coffee Products According to DIN 20481 by Edgar Naegele from where this figure is taken:


[![enter image description here](https://i.stack.imgur.com/cDF27.png)](https://i.stack.imgur.com/cDF27.png)


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