How do I extract free amino acids form leaf tissue?

[Tony Larson]

I'd like to know a method to extract free amino acids from small
(5-100 mg) amounts of plant leaf tissue.  These will than be
derivatized and analyzed by either HPLC or GC.  I would particularly
like to know the best way to clean up the extracts, to remove
background contaminants, in as small a working volume as possible
before derivatization.  This is because I will need to process a large
number of samples.