cis/trans FAME Isomers

Fatty acids in the cis configuration are the dominant form in nature. Correspondingly, enzymes have evolved to efficiently digest and metabolize them with a high degree of specificity. Conversely, trans fatty acids are relatively rare in nature. However, because they can increase the shelf life and flavor stability of foods containing them, they have become predominant synthetic additives to processed foods, especially fried foods and baked goods.

Unfortunately, trans fatty acids, formed by partial hydrogenation of vegetable oil, interfere with natural metabolic process, resulting in an imbalance of the LDL:HDL ratio, and also increasing lipoprotein(a) levels. Studies have linked their nutritional contribution to be similar to that of saturated fatty acids, possibly playing a role in the heightened risk of coronary artery disease.

Because trans fatty acids have adverse health consequences and no known nutritional benefits over other fats, consumer groups have pressured manufacturers and restaurants for their elimination. Many regulatory agencies worldwide now require content labeling to inform buyers of ′trans fat′ levels of foods and some dietary supplements.

The differences between cis isomer FAMEs and trans isomer FAMEs of the same carbon length and degree of unsaturation are very small. Therefore, very efficient capillary GC columns with highly polar phases are required.
  • The highly polar SP-2560 column was specifically designed for the separation of geometric-positional (cis/trans) isomers of FAMEs, and is extremely effective for special FAME applications including the separation of FAMEs in hydrogenated vegetable oil samples. This well-established column is specified in many methods.
  • The extremely polar SLB-IL111 column exhibits the highest polarity of any GC phase, providing an alternative selectivity for FAME applications typically performed on SP-2560 and SP-2380 columns. It is able to provide resolution of some key isomers that cannot be resolved on the SP-2560 or SP-2380 columns.
  • The highly polar SP-2380 column allows the separation of geometric (cis/trans) isomers as a group. The phase is stabilized, providing a maximum temperature slightly higher than the popular SP-2560 column. It is available in shorter column lengths than the SP-2560, therefore, useful for short analyses where detailed resolution is not necessary.

Technical Article:
Compehensive Determination of Trans Fats in Cookies using SP-2560 and SLB-IL111 GC Columns after Silver-Ion SPE Fractionation
Fast GC Analysis of Detailed cis/trans Fatty Acid Methyl Esters (FAMEs) on the 75 m SP-2560 Capillary Column
New cis/trans FAME Standard for Optimizing GC System Performance