Filpi replied: "Hello there, At elevated temperatures the entropic driving force for scission in molecules rises. This is because high temperatures favour the formation more molecules, as more molecules have more entropy than fewer. This is typical of cracking type reactions. Upto 300 deg C, we get a set of decomposition pathways, typical to all carbohydrates and many amino acids. In fact, the thermal decomposition products are indistinguishable from those of other 'reducing sugars' The 'Maillard reaction' is responsible for the browning of foods when you cook them, like toast, and also the aroma of coffee etc. This the key pathway to talk about. Unfortunately, the Wiki article does not have a mechanism for this; I'll try and explain it here, but its difficult without being silly verbose and without pictures! The principle mode of degradation is dehydration and intra-molecular redox. The decomposition is not clean and produces a varied distribution of products, although principally furfural is produced (accounting for some 60-80% of the products). Traces of furoic acid, furil and similar products are produced, the oxidation products of furfural. The formation of these cyclic products involves ring-opening of the vit c, some other reactions and then the cycle reforms. C13 labelling experiments have shown that the ring does in fact open, and reform. The main pathway is as follows: Keto-enol tautomerism, to the ketone form. Hydrolysis of the lactone, followed by decarboxylation, loosing the terminal carboxyl group. The final few steps involve shuffling the newly formed double bond down along the chain by means of water addition/elimination; and lastly reformation of the 5 membered furan cycle. Hundreds of trace products are produced, which represent different chunks of the vit c molecule, and the multitude of reactions between these products. The product of these reactions are typically furan derivatives. If you want to know more about this, ask another question; no point me going off topic if it's not what you're after! Cheerio"

killerjoe777 replied: "This is a tricky problem depending on what resources you have access to and how much time and/or money you are willing to put into this project. There are several analytical techniques that would hopefully be fairly straight forward, however require access to analytical instruments. Ion chromatography (ion exchange on weak organic acids) and gas chromatography with an ascorbic acid standard might be easy depending on what other ingredients are present in your samples, though preparing your samples might be tedious. Another option is using titration, this method requiring access to glassware (buret, beakers, etc.) and a few chemicals. I searched google for analysis "vitiman C" and the first link that pops up (see below) gives a procedure for titration determination."