Actually, I mentioned this to a co-worker who pointed me at:

http://www.medicalnewstoday.com/medi...p?newsid=43343

which is an article about a home caffeine test that the Wash U
medical school folks are developing.

The standard old-fashioned test is to mix with an oxidizing agent,
then ammonia is added until a color change is seen. In the case
of tea, you have to clear the tannins out by adding a little bit of
portland cement first... the cement adsorbs the tannins and gives
you a cup of clear liquid. These days with cheap mass spectrometry
I don't think anyone bothers but there's no reason you can't do the
caffeine titres in a kitchen at home. I don't know how specific it is
for caffeine, though, and it may also detect other related xanthines
at the same time.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."