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Determination of Free Fatty Acids in Edible Oils with the Use of a Variable Filter Array IR Spectrometer
Author(s) -
Li Yue,
GarcíaGonzález Diego L.,
Yu Xiuzhu,
Voort Frederik R.
Publication year - 2008
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/s11746-008-1232-z
Subject(s) - methanol , spectrometer , chemistry , biodiesel , absorbance , fourier transform infrared spectroscopy , extraction (chemistry) , chromatography , solvent , analytical chemistry (journal) , infrared spectroscopy , absorption (acoustics) , materials science , organic chemistry , catalysis , chemical engineering , physics , quantum mechanics , engineering , composite material
The feasibility of employing a portable variable filter array (VFA) IR spectrometer equipped with a transmission flow cell to quantitatively analyze edible oils or biodiesel feedstocks for free fatty acids (FFA) was evaluated. The approach to FFA determination employed was based on a previously reported FTIR method that involves the extraction of FFAs into methanol containing the base NaHNCN, which converts the FFAs to their salts, followed by measurement of the carboxylate absorbance at ~1,573 cm −1 in the spectrum of the methanol phase. When this methodology was implemented on the low‐resolution VFA‐IR spectrometer, the analytical performance was comparable to that of conventional FTIR instrumentation at FFA concentrations of <1%. However, at higher FFA levels, the relatively weak pulsed IR source of the VFA‐IR spectrometer was found to provide insufficient energy for accurate measurement of the carboxylate absorption superimposed on the strong methanol absorption at ~1,450 cm −1 . By changing the extraction solvent to ethanol (EtOH), good spectra and calibrations could be obtained over an FFA range of 0–5%, having an overall SD of ±0.07% FFA. Based on this assessment, a VFA‐IR spectrometer provides an economical instrumental means for at‐line monitoring of FFA levels in crude and refined edible oils and biodiesel feedstocks, capable of analyzing ~20–30 prepared samples per hour.