Due to the destructive oxidation hydrolysis at higher PH,
this results in the opening of the lactone ring
of the ascorbic acid and loose the vitamin activity. These processes naturally occurre in fruits, and some
amounts of diketogulonic acid is present in the fruits (Geigertj et al., 1981). As the diketogulonic acid has
keto group, it should give the osazone with DNPH as that of ascorbic acid and should give the colored complex
on treatment with 85% H2SO4. Thus there is chance of error in this method. But actually this cannot interfere
with the ascorbic acid. Here diketogulonic acid was prepared by the acid hydrolysis of ascorbic acid. The
spectrum shows that there is no considerable absorption peak near the 280nm (the absorption maxima of
DNPH complex of ascorbic acid).