Temperature-Sensitive Resolution of cis- and trans-Fatty Acid Isomers of Partially Hydrogenated Vegetable Oils on SP-2560 and CP-Sil 88 Capillary Columns

Abstract

Abstract This study examines the effect of the column operating temperature of 100 m SP-2560 and CP-Sil 88 capillary gas chromatographic (GC) columns on the separation of cis- and trans-octadecenoic (18:1) isomers in partially hydrogenated vegetable oils. The overlapping GC peaks were measured at column isothermal temperatures of 170, 175, 180, 185, and 190°C. With both columns, isothermal operation at 180°C produced the fewest overlapping peaks of the cis and trans isomers. At this temperature, all trans-18:1 isomers, except 13t-18:1 (t = trans), 14t-18:1, and 15t-18:1 isomers were resolved from 14t-18:1, the cis-18:1 isomers. The peaks of the 13t-18:1 and 14t-18:1 isomer pair, which always elute together, overlapped peaks of the 6c-18:1 (c = cis), 7c-18:1, and 8c-18:1 isomers; the peak of the 15t-18:1 isomer overlapped the major cis-18:1 peak, which was mainly due to 9c-18:1. Isothermal operations above or below 180°C produced some additional overlapping problems. At 185 and 190°C, the peaks of the 16t-18:1 and 13c-18:1 isomers overlapped. At 175 and 170°C, the 16t-18:1 peak overlapped the 14c-18:1 peak, and the peaks of the 13t + 14t-18:1 isomer pair partially overlapped the major cis-18:1 peak. The separation of 11c-20:1 and α-linolenic acid and its geometric isomers was also affected by the column operating temperature. Isothermal operation of the SP-2560 column at 180°C produced a baseline separation of 11c-20:1 and α-linolenic acid and its geometric isomers, whereas with the CP-Sil 88 column the best resolution was obtained at 170°C. The results of this study show that the SP-2560 capillary column has a slight advantage over the CP-Sil 88 column for the simultaneous resolution of all the fatty acids generally found in partially hydrogenated vegetable oils.