SB-ATR FTIR Spectroscopic Monitoring of Free Fatty Acids in Commercially Available Nigella sativa (Kalonji) Oil

Free fatty acids (FFA) in Nigella sativa (N. sativa) commercial and seed oil were determined using single-bounce attenuated total reflectance (SB-ATR) Fourier transform infrared (FTIR) spectroscopy. Gravimetrical mixing was done by adding 0.1–40% oleic acids in neutralized N. sativa oil containing 0.1% FFA. FTIR spectroscopy technique and partial least square (PLS) calibration were used to detect the absorption region of carbonyl (C=O) which is in the range of 1690–1727 cm−1. The results of PLS calibration model and root mean square error of calibration (RMSEC) are 0.999 and 0.449, respectively. Comparing the FFA obtained in N. sativa oil by using FTIR with the FFA obtained using AOCS titrimetric method shows a positive correlation and confirms that the described method is a useful procedure.