I have to prove scientifically why a sodium ascorbate solution in water turns yellowish - reddish over time. I know ascorbic acid is supposed to oxidize into dehydroascorbic acid, and the latter then oxidizes into more subproducts... But I have to prove this by using UV-vis spectroscopy and whenever I analyze the yellowish solution the only peak I see is the ascorbic acid peak (around 262 nm). Why don't I see the dehydroascorbic acid peak (210 nm) or even other peaks related to the other subproducts ? Update: I found this graph on a published article and I was expecting to obtain something like it:
Below are the peaks of a fresh sodium ascorbate 10% w/w solution (orange peak) and a solution with the same concentration that has been aged for 50 days and has acquired a deep yellow color (green peak). Both of the solutions have been diluted to 1:80.000 in water for the UV-vis analysis. The ascorbic acid in the aged solution has obviously degraded in some way since the peak is lower, but why are there no new peaks regarding the degradation products ?