1118 Rapid and Direct Iodine Value and Saponification Number Determination of Fats and Oils by Attenuated Total Reflectance/Fourier Transform Infrared Spectroscopy F.R. van de Voort*, J. Sedman, G. Emo and A.A. Ismail Department of Food Science and Agricultural Chemistry, Macdonald Campus of McGill University, Ste. Anne de Bellevue, Qu6bec, Canada H9X 1CO A simple, rapid and reproducible method of determining the iodine value (IV) and saponification number (SN) for fats and oils was developed with an attenuated total refle~ tance/Fourier transform infrared spectrometer and com- mercially available triglycerides as calibration standards. Partial least squares was used to determine the spectral regions correlating with the known chemical IV and SN values, and the calibration set was augmented with addi- tional standards generated by spectral co-adding tech- niques. The calibration model obtained was used to analyze commercially available fats and oils with a wide range of IV and SN values, and the results were compared to the values obtained by American Oil Chemists' Society methods. With the spectrometer calibrated and program- med, IV and SN results could be obtained within 2-3 min per sample, a major improvement over conventional wet chemical methods. KEY WORDS: Edible oils, fats, Fourier transform infrared spec- troscopy, iodine value, saponification number. Fats and oils from a wide variety of sources ave important to the food industry and other industrial sectors. In almost every situation, the general characterization of such oils and the monitoring of modifications they may undergo during processing are important relative to their quality, functionali- ty and economic value Typical analyses that are important include iodine value {degree of unsaturation), saponification number (average molecular weight), moisture content, level of trans fatty acids, free fatty acids, peroxide value and 2-thiobarbituric acid (TBA) number. Iodine value (IV) and saponification number (SN) are two of the more common analyses used for characterizing fats and oils, with IV be- ing crucial in monitoring hydrogenation processes. Both of these analyses are tedious, time consuming and expensive, but needed on a routine basis. The possibility of developing a rapid method for IV deter- mination based on infrared spectroscopic analysis has been investigated by several workers. Arnold and Hartung (1), using a dispersive infrared spectrometer, determined IV for a variety of fats and oils from the ratio of intensities of the olefinic and aliphatic C~H stretching bands in their infrared spectr~ The samples were dissolved in CCI 4 and analyzed in an infrared transmission cell. Bernard and Sims (2) de- veloped a similar infrared method except that they ana- lyzed oils in their neat form and used the weak C=C stretch- ing band (~ 1660 cm -1) to determine total unsaturation. Recently, Afran and Newbery (3) employed Fourier trans- form infrared (FTIR) spectroscopy and an attenuated total reflectance (ATR) sampling technique for the evaluation of unsaturation in edible oils and compared their results to *Towhom correspondence should be addressed at Departmentof Food Science and AgriculturalChemistry, Macdonald Campusof McGill University, 21,111 Lakeshore Road, Ste. Annede Bellevue,Quebec, Canada H9X 1CO. those obtained by gas chromatography. Similarly to Arnold and Hartung (1), they based their method on the measur~ ment of peak height ratios in the C-H stretching region. In our laboratory we have been investigating the develop- ment of general-purpose quality control methods based on FTIR spectroscopy (4-6). FTIR spectrometers are a major advance over conventional grating instruments in that they have more energy; excellent wavenumber reproducibility and accuracy (laser-calibrated); data manipulation capabilities (subtraction, ratio determination, derivative spectra and deconvolution); and advanced chemometric software to han- dle calibration development (7,8). Systems such as the Nicc~ let 8200 series FTIR spectrometers (Nicolet Instrument Inn, Madison, WI) include the analytical software and macro programming capabilities required to automate analytical procedures. FTIR, coupled with an ATR accessory, which simplifies many of the sample handling problems asociated with IR analyses, provides a new approach to quality con- trol applications in the food sector. This paper describes the development of a practical, automated ATR/FTIR method to determine IV and SN simultaneously by the partial least squares (PLS) technique for multivariate analysis of the FTIR data (9) and using pure triglycerides as a basis for calibration rather than pre~analyzed oils. EXPERIMENTAL PROCEDURES Calibration standards. Reagent-grade trigiyceride stan- dards (purity > 98%) tricaproin (C6), tricaprylin (C8), tri- caprin (C10), trilaurin (C12), tripalmitin (C16), tristearin (C18), triolein (C18:1c), trielaidin (C18:lt), trilinolein (C18:2c), trilinolelaidin (C18:2t) and trilinoleinin (C18:3c) were obtained from Sigma Chemical Company (St. Louis, MO). These triglycerides were chosen to cover a range of molecular weights and degrees of unsaturation. Based on their known structures, their theoretical IV and SN were calculated and used as reference values for subsequent calibration development. Instrumentation. For this work a Nicolet 8210 Fourier transform infrared spectrometer (Nicolet Instrument Inn) was used, equipped with a horizontal germanium ATR ac- cessory placed in the instrument optical cavity. The in- strument was purged with a Baiston dryer (Bal- ston, Lexington, MA) to minimize water vapor and CO2 interferences. The ATR plate was heated to 60°C (+_ 0.2°C) by attaching four 25W strips of heating tape onto the plate, with the temperature controlled by an Omega CN4400 temperature controller (Omega Engineering, Stamford, CT). Calibration. For the calibration, all spectra were col- lected from 128 scans at 16 cm -1 resolution. Prior to cali- bration or analysis, the ATR crystal was cleaned with a 1% Triton X-100 solution (Sigma Chemical) followed by hexane and dried, and the temperature of the ATR crystal was equilibrated to 60°C. A reference background emit- tance spectrum was taken of the clean cyrstal and stored to disk. The triglyceride standards were equilibrated to JAOCS, Vol. 69, no. 11 (November 1992)