Titrimetric Method for Reduced Vitamin C 1. Extract with metaphosphoric acid (HPO3) in HOAC. 2. Titrate with 2, 6-dichloroindophenol (blue). At end point, rose pink (2, 6-dichloroindophenol in acidic condition).Titrimetric Method for Reduced Vitamin C 1. Extract with metaphosphoric acid (HPO3) in HOAC. 2. Titrate with 2, 6-dichloroindophenol (blue). At end point, rose pink (2, 6-dichloroindophenol in acidic condition)