Two-dimensional correlation analysis of oxidation process of ascorbic acid at different temperature by Fourier transform infrared spectroscopy

The Fourier transform infrared ( FTIR) spectroscopy and two-dimensional correlation analysis were applied to study the oxidation process of the solid ascorbic acid from 20degreesC to 160degreesC. The changes of absorption peaks of ascorbic acid in the FTIR spectra were inconspicuous during heating up. With the help of 2D correlation analysis, the resolution of the spectra was improved, the peak at 1674 cm(-1) on FTIR was distinguished as two autopeaks which were assigned to the vibrations of the C=O group of keto form and the C C group of hydrin form respectively. The two forms are the isomers of the ascorbic acid. Also the relationship between the different groups of ascorbic acid and the sequence of them to change during the oxidation process were illustrated. The groups C=O, C=C and C-O-C of ascorbic acid interact each other, and the sequences of change are C=O. C-O-C and. C=C. The results are in good accordance with the oxidation mechanism of ascorbic acid. In conclusion, the 2D correlation analysis of FTIR can be a new method to analyze the microcosmic dynamic change of the structure of ascorbic acid during the oxidation process and also offers an important theory gist to the study of oxidation mechanism of ascorbic acid.