Determination of low trans levels in refined oils by Fourier transform infrared spectroscopy

A Nicolet 410 Fourier (FTIR) spectrophotometer, equipped with a DGTS detector and a sample cell with NaCl windows (nominal pathlength = 50 mu m), was used for the development of an FTIR method for routine analysis of low trans levels in physically refined oils. The approach of the study differed from those previously described in that a separate calibration curve was established for each type of oil. Quantitation was established by use of Basic Quant Software(R) and by measuring the peak height at 967 cm(-1) relative to a baseline drawn between 1002 and 932 cm(-1). The slope of the different calibration curves established in six vegetable oils (soybean, corn, sunflower, high-oleic sunflower, low-erucic rapeseed, and high-erucic rapeseed) was close to 1 (0.9942-1.0041), and correlation coefficients (r(2)) were rather good (0.9990-0.9999). FTIR spectra of 20 soybean oil samples were collected and quantitated with the different calibrations. Compared to previous reported literature data, increased accuracy (mean difference = 0.05%; standard deviation of difference = 0.11%) and reproducibility (r(2) = 0.09-0.12%) were obtained when the FTIR spectra were quantitated with a calibration curve based on 10 physically refined soybean oil samples.