Determination of the acid values of edible oils via FTIR spectroscopy based on the OH stretching band

• A simple method to determine the acid value of the edible oil with FTIR spectroscopy by using the OH stretching band.
• Details of the FTIR spectrum of the oil sample were measured with a dilute solution in carbon tetrachloride.
• The sample was placed into an infrared quartz cuvette to collect the FTIR spectrum.
• The sample thickness was controlled exactly with an infrared quartz cell.

A new method for determining the acid values (AVs) of edible oils based on the OH stretching band was developed. The oil sample was diluted with carbon tetrachloride and was placed in a quartz cuvette with a thickness of 1 cm to record the FTIR spectrum. The peak at 3535 cm−1, which corresponds to the OH stretch of the carboxyl group in free fatty acids, together with the peak valley at 3508 cm−1 and the spectral data in the range of 3340–3390 cm−1 were used to determine the AV of the edible oil. The excellent linear relationship between the AVs measured in this work and those measured using a titration method, with a correlation coefficient (R) of 0.9929, indicates that the present procedure can be applied as an alternative to the classic method for determining the AVs of edible oils.