Dichlorophenolindophenol reduced and becomes colorless, the resultant increase in light transmittance can be measured using a spectrophotometer. DCPIP can also be used as an indicator for vitamin C. If vitamin C, which is a good reducing agent, is present, the blue dye, which turns pink in acid conditions, is reduced to a colorless compound by ascorbic acid. This reaction is a redox reaction: vitamin C (ascorbic acid) is oxidized to dehydroascorbic acid, and DCPIP is reduced to the colorless compound DCPIPH In this titration, when all the ascorbic acid in the solution has been used up, there will not be any
Folinic acid to be metabolized in the liver before it could support growth of "L. citrovorum." The synthesis of citrovorum factor by liver cells in culture was eventually accomplished from pteroylglutamic acid in the presence of suitable concentrations of ascorbic acid. The simultaneous addition of sodium formate to such systems resulted in increased citrovorum factor activity in the cell-free supernatants (producing, as now known, the 5-formyl derivative), and from this method of preparation of large amounts of the factor, its structure as levo-folinic acid (5-formyl tetrahydrofolic acid) was eventually deduced. Folinic acid should be distinguished from folic acid (vitamin B). However, folinic