Monitoring of Polymerized Triglycerides in Deep-Frying Oil by On-Line GPC-FTIR Spectrometry Using the Science Based Calibration Multivariate Approach Julia Kuligowski, Guillermo Quinta ´s, Salvador Garrigues, Miguel de la Guardia & Department of Analytical Chemistry, Universidad de Valencia, Edificio Jero ´nimo Mun ˜oz, 50th Dr. Moliner, 46100 Burjassot, Spain; E-Mail: miguel.delaguardia@uv.es Received: 30 July 2009 / Revised: 14 October 2009 / Accepted: 9 November 2009 Online publication: 15 December 2009 Abstract On-line gel permeation chromatography Fourier transform infrared (GPC-FTIR) is proposed as detection technique for the determination of the total polymer triacylglyceride (PTG) content in olive oil as an alternative to other conventional detectors such as the evaporative light scattering detector (ELSD) or the refraction index detector (RID). FTIR detection allowed confirmation additionally to quantification of the analytes via their characteristic infrared spectra. For the extraction of chromatograms, a multivariate method called science based calibration (SBC) was used. The SBC method employed a reference spectrum of triacylglycerides (TG) extracted from the injection of a fresh olive oil sample and data obtained from a blank injection as ‘noise’ matrix, to estimate a regression vector subsequently used to predict the relative concentration of the analyte during the GPC run. Results found evidenced that the use of SBC improved the selectivity, sensitivity and repeatability of the GPC-FTIR measurements as compared to the ‘classical’ approach based on the measurement of the spectral area in a defined spectral range. The developed method provided a limit of detection for PTGs of 0.19 mg mL -1 , which corre- sponds to a 0.65% w/w for an oil sample mass of 300 mg. Keywords Gel permeation chromatography-infrared spectrometry Science based calibration Polymerized triacylglycerides Olive oil Introduction Olive oil is used worldwide for the prep- aration of a variety of food products. However, when heated it is subjected to a series of degradation reactions. This degradation process varies according to different factors such as the type of food frying (composition, continuous or intermittent frying, quantity of fried food), fryer (capacity, surface, T, metals in contact with the oil), oil (nature, ther- mostabillity, amount of fresh oil) and others including the presence of protec- tive gas, antioxidants or antifoams [1]. Frying olive oil, a wide variety of products can result from the different chemical reactions of the unsaturated fatty acyl groups in the different triacyl- glycerides (TGs). According to their molecular weight and structure, the non- volatile compounds formed during a frying process can be classified in three groups: (1) polymer triacylglycerides (PTGs) (dimers and oligomers) are the major compounds in used frying fats and are also the major degradation com- pounds formed during frying [2]; (2) oxidized monomers; these are TGs with at least one of their fatty acyl groups oxidized and with a molecular weight similar to the parent TGs; and (3) TGs containing short-chain components and volatile compounds with molecular weights lower than those of parent TGs. All the aforementioned products (including those obtained by oxidation, hydrolysis and polymerization) take place in the unsaturated fatty acyl groups attached to the glyceridic back- bone and, therefore, the stable final products are triglyceride monomers, 2010, 71, 201–209 DOI: 10.1365/s10337-009-1426-z 0009-5893/10/02 Ó 2009 Vieweg+Teubner | GWV Fachverlage GmbH Original Chromatographia 2010, 71, February (No. 3/4) 201