Dear Allgae;
To inform you about Caffeine you may read for this times in “Wiki”.
You will see there that Caffeine is an Organic Base, because the lot of Nitrogens.
That means that you can moderate its solubility, especially for water.
So the basic recipe would be:
Take 300ml cola (a can) into a 1.0 Liter “Separatory Funnel” and add slowly (Why?) concentrated NaHCO3 Solution till you reaches a pH 6 till 7 (at least higher then 5). Now the Caffeine will be back to the base state and is easy and quantitave to be extracted with your “DCM”. Do the Extraction with 3 till 5 times a small volume of DCM to be as quantitative as possible.
The rest of the procedure depends of your main goal, that means if you need it quantitative or preparative. Primary you can do with a Spectrometer, secondary by first drying the DCM solution and finally evaporation the DCM.
I hope this may be of help to you
Good Luck!
ARGOS++