[kwroyer]

I want to be  able to determine the amount of caffeine I am getting in a cup of coffee. Simple that can be done at the time of consumption. A need would be to verify if a coffee is decafinatied.
I have searched many sites including very technical ones but they only discuss the effects of caffeine on various human and animal conditions.

[lemonoman]

I don't think you're going to find one.  Coffee is a HUGE matrix, with thousands of chemicals in it.  A single test that can instantaneously determine the caffeine content of a beverage doesn't exist (to my knowledge).  Chromatographic methods are currently one of the best ways to get this value.

Wanna find out how complex a coffee matrix REALLY is?  Go to Analysis of roasted coffee bean volatiles by using comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry - Journal of Chromatography A, Volume 1054, Issues 1-2, 29 October 2004, Pages 57-65 by Danielle Ryan, Robert Shellie, Peter Tranchida, Alessandro Casilli, Luigi Mondello and Philip Marriott

Want a pile of articles about caffeine (including one about, "Caffeine effects on resting-state arousal"  ) ? Try This page from Elsevier

Good luck!

[constant thinker]

I have an idea.

Just drink the coffee. If you feel perkier later then you got caffeine in it.

lemonoman does have a point thought. I looked up what was in coffee other than caffeine once. I got a huge list of molecules.