I'd be very grateful if someone could suggest a reliable method for measurement of ascorbic and dehydroascorbic acids from plant (ie. non-fruit) tissue. I've tried a few methods with a fairly standard C18 RP column, but so far the main problem has been in detecting the dehydroascorbate; I need this measurement for redox calculations. Details of suitable mobile phase/running conditions would be a big help.

Careful! It may well be that there is no DHA in living material, except in a transitory state. Living material has large amounts of sulfhydril groups and other reducing agents which reduce DHA immediatly to Asc.
We have experimented with converting DHA to osazones with dinitrophenyl hydrazine, but donīt like this method, as two isomeric and easily interconvertible osazones are produced, among other negative aspects. To get the Asc you would need to oxidize it to DHA, etc. The details are too extensive to list here, but since we are also still in the process of getting at a HPLC of Asc, etc., it might make sense to continue contacts.

Dear Emma
In LCWorldtalk Vol 2, no 1 Oct, 1997 (from Shimadzu) is described a metod for ascorbic acid and dehydroascorbic acid. ( by Yoshihide Yasui and Morimasa Hayashi)