The use of ATR-FTIR spectroscopy to measure changes in the oxirane content and iodine value of vegetable oils during epoxidation

A rapid attenuated total reflectance Fourier transform infrared (ATR-FTIR) method was developed to simultaneously measure for vegetable oils both their oxirane oxygen content (OOC) and the change in their iodine values (IV) that occur during their epoxidation. The method uses the peak area of the epoxy functional group absorption (1497.3-1432.0 cm(-1)) to measure OOC and the H-C=absorption associated with a carbon-carbon double bond (3017.5-3004.2 cm(-1)) to determine the relative changes in iodine value (Delta IV). Calibrations were developed by gravimetrically blending epoxidized canola oil (ECO) with unreacted canola oil (CO) to vary both OOC and IV. Oils including canola, camelina, and flaxseed were epoxidized, during which the OOC and DIV were tracked as a function of time using both the new ATR-FTIR procedures and the standard ASTM methods. Both the OOC and DIV values measured by the ATR-FTIR method correlate well to values from standard methods (R-2 >= 0.992 and mean relative error of <3%). The FTIR procedure is simple and fast to perform and facilitates the determination of selectivity (conversion of double bonds into oxirane group) and the end-point for the epoxidation reaction, which requires measurement of both OOC and IV.