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I know that the decaffeination process is not perfect and that it leaves some caffeine. I've looked online and there was a company in 2009 that offered caffeine test strips but they seem to be no longer offered.

Another approach would be to use a GCMS, but used GCMS devices are expensive and it takes alot of effort to keep them in calibration (at least it did when I was in college).

Are there services where I can send a sample off and they will tell me how much caffeine they contain? Failing that, how would I reasonably test how much caffeine is in my tea and coffee?

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    $\begingroup$ Why do you want to do that? $\endgroup$
    – Karl
    Commented Mar 2, 2021 at 17:32
  • $\begingroup$ Yes, there are many labs that do food testing, and include caffeine testing among their services. But it's expensive; the pricing is designed for businesses rather than consumers. E.g., mydrinkbeverages.com/services/new-beverage-development/… does caffeine testing by LC/UV, but it costs $150 per sample (search this document for "caffeine": 4557656.app.netsuite.com/core/media/… ) $\endgroup$
    – theorist
    Commented Mar 3, 2021 at 3:22
  • $\begingroup$ Why do it yourself when others have already done the analysis? As this report shows. $\endgroup$
    – matt_black
    Commented Mar 3, 2021 at 12:08
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    $\begingroup$ I want to do it for myself because every cup is different. And every batch of tea is different. And I want to know what’s going on with my food, not other food. $\endgroup$
    – vy32
    Commented Mar 3, 2021 at 19:03

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I originally thought that UV/vis on tea samples (the liquid from contacting tea with hot water) would not be a good method as the tea is a complex mixture. I think that with a lot of clean up that it would be possible to make the measurement. I know that HPLC with a UV detector would be the best method of making the measurement.

But after reading the work of a famous tea and coffee chemist, I have come to the view that direct measurement of the brewed tea would work using measurement at 273 nm.

There was an electrochemist at Imperial College named Michael Spiro, he did a lot of work on tea and coffee. One of the things he did was to model and measure the brewing process which occurs when you make a cup of tea.

See for example

Kinetics and equilibria of tea infusion, Part 15. Transport of caffeine across a teabag membrane in a modified rotating diffusion cell, Michael Spiro and Deogratius Jaganyi, Food Chemistry, Volume 69, Issue 2, 1 May 2000, Pages 119-124

I would not want to use GCMS for caffine as the caffine is so very polar.

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  • $\begingroup$ Thanks. I wasn’t aware that GCMS wouldn’t work for this. $\endgroup$
    – vy32
    Commented Oct 12, 2022 at 9:27
  • $\begingroup$ Also a great reference! $\endgroup$
    – vy32
    Commented Oct 12, 2022 at 9:27
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You may try to extract the caffeine with DCM and determine its concentration by spectrophotometry.

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  • $\begingroup$ So the idea would be to get a used UV spectrometer? $\endgroup$
    – vy32
    Commented Mar 3, 2021 at 19:03
  • $\begingroup$ I would suggest so. See ncbi.nlm.nih.gov/pmc/articles/PMC4641934. The spectrum of caffeine has a peak of absorbance at 274 nm (UV). $\endgroup$
    – 1__
    Commented Mar 3, 2021 at 19:28

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