Observations on the use of 2,4-dinitrophenylhydrazine and of 2,6-dichlorophenolindophenol for the determination of vitamin C in raw and in heat-treated milk.

A study has been made of methods using 2,4-dinitrophenylhydrazine (DNPH) or 2,6-dichlorophenolindophenol (DCP) for the determination of vitamin C (ascorbic acid+dehydroascorbic acid) in raw, UHT processed, evaporated and sterilized milk. Interfering substances were not detected in milk that had received a heat treatment no more severe than 145°C for 4 s (UHT process), so that either reagent could be used. With more drastic heat treatment, interfering substances were formed and only the DNPH method with column and thin layer chromatography of the DNPH derivatives was specific for vitamin C. With in-bottle sterilized milk, the values for ascorbic acid were (in mg/100 ml) 1·16 (DCP method with H 2 S reduction); 0·58 (DCP method with Escherichia coli reduction); 0·64 (DNPH method); 0·33 (DNPH method combined with chromatography). In our experience the DNPH method combined with chromatography of the derivatives is highly specific for vitamin C and should be used to check the results obtained by other and simpler methods.