Ascorbic acid, determination differential method

A study of the relaxational transitions and related heat capacity anomalies for galactose and fructose has been described which employs calorimetric methods. The kinetics of solution oxidation of L-ascorbic acid have been studied using an isothermal microcalorimeter. Differential scanning calorimetry (DSC) has been used to measure solid state co-crystallization of sugar alcohols (xylitol, o-sorbitol and D-mannitol), and the thermal behaviour of anticoagulant heparins. Thermal measurements indicate a role for the structural transition from hydrated P-CD to dehydrated P-CD. Calorimetry was used to establish thermodynamic parameters for (1 1) complexation equilibrium of citric acid and P-CD in water. Several thermal techniques were used to study the decomposition of p-CD inclusion complexes of ferrocene and derivatives. DSC and derivative thermogravimetric measurements have been reported for crystalline cytidine and deoxycytidine. Heats of formation have been determined for a-D-glucose esters and compared with semiempirical quantum mechanical calculations. ... 

Differential Method for Determination of Ascorbic Acid, Dehydro-ascorbic Acid, and Diketogulonic Acid. Method of Roe, Mills, Oesterling,... 

The methods of Roe and Kuether (21) and of Roe and Oesterling (22) for the determination of vitamin C do not differentiate between ascorbic acid (AsA), dehydroascorbic acid (DHA), and diketogulonic acid (DKA). The same basic principle is applied to the determination of the three substances (23), the differentiation being made through the use of H2S which reduces DHA to AsA and does not reduce DKA under the conditions used. In analyzing an extract which contains all three forms of vitamin C, one aliquot is reduced with H2S, a second aliquot is left untreated, and a third aliquot is treated with bromine. After coupling with 2,4-dinitrophenyl-hydrazine the derivative in the first aliquot is that of DKA, the one in the second aliquot is that of DHA and DKA, and the one in the third aliquot is that of AsA, DHA, and DKA. Appropriate subtraction of the values obtained by colorimetric measurements will give the value for each component. 

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