I've done a bit of reasearch into TBA assays regarding its Malondialdehyde reaction and its uses in testing various fruit samples. However one thing that many of these have in common is that they note that after about 6 hours the photospectrometer results begin to vary and they Reccommend that new TBA be prepared daily.
Now as far as I've found there is nothing that has looked into why this happens or how to preserve the reagent longer. From my own thinking it shouldn't be particularly unstable and the best I can find is a mention of a solution with sodium sulfate that "keeps for up to 1 month" in a fairly old paper that I'm not sure tested to the same degree of specificity as others I've read.
Does anyone have any experience/ideas/suggestions as to what could be causing this? 4,6 Dihydroxy-2-mercaptopyrimidine in case it helps someone out.