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. 1. Introduction Herbal products are increasingly used as alternatives to orthodox drugs or medicine. Nigella sativa plant belongs to the Ranunculaceae family and it is commonly found in South, Southwest Asia, North Africa, and Southern Europe where it has been used traditionally as medicinal plant and spice since ancient time [1]. In Pakistan and India, N. sativa is cultivated as an annual herb and is commonly called kalonji [2]; other names are black cumin or black seed or Roman coriander or nutmeg flower or fennel flower [3]. It has been commonly used in traditional medicine as natural remedy for various diseases for over 2000 years in the Middle Eastern folk medicines [4]. N. sativa is used as seasoning and flavouring supplement for food, bread, pickles, and bakery products [5]. N. sativa oil or extract has protective and curative actions. Extracts of N. sativa have been used for the treatment of hypertension, asthma, inflammation, diabetes, eczema, bronchitis, fever, headache, dizziness, cough, and influenza [6, 7]. It has been reported in the literature that seed of N. sativa found to be diuretic, carminative, stimulant, galactagogue and emmenagogue, and antipyretic [8]. Oil is a complex mixture that contains fatty acids, vitamins, pigments, volatile, and antioxidative components. The hydrolysis of oil results in the formation of FFA and glycerol residues. Among the oil quality parameters, FFA is the major cause of flavor deterioration and shelf life of the oil [9]. Therefore, it is a crucial factor associated with the quality and economic value of edible oils, especially for unrefined high value oils such as olive and N. sativa oil. Generally, FFA content is determined by titration method. According to the procedure, oil is dissolved in diethyl ether or
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