Trans Fatty Acid Analyses in Samples of Marine Origin: The Risk of False Positives

Abstract

At conditions commonly applied for trans fatty analyses by gas chromatography, fatty acids naturally occurring in marine lipids may overlap chromatographically with C16 and C18 trans fatty acids and lead to false positives. Elution patterns were studied by tracking retention indices at shifting temperature conditions on two cyanopropyl-coated capillary columns. Most overlaps can be avoided by selecting the right chromatographic conditions, but it was not possible to find a single condition that eliminates the risk of overlap between trans fatty acids and interferents. In total, 17 compounds were identified as potential interferents, and the amounts of these compounds were quantified in various samples of marine origin. The interferents that will most likely contribute to incorrect assessments of trans fatty acids in marine lipids are probably 18:3 n-4 and 18:1 n-11.

Separation of the Fatty Acids in Menhaden Oil as Methyl Esters with a Highly Polar Ionic Liquid Gas Chromatographic Column and Identification by Time of Flight Mass spectrometry

“…However, five FAME could not be resolved as individual peaks using either temperature program and they included 18:2n-6, 16:4n-1, 18:3n-3, t9-19:1 and 23:0 [3]. A similar conclusion was reached after combining the results of marine oil analyses using a BPX-70 column (bonded cyanopropyl polysilphenylene siloxane polymer phase equivalent to 70 % CPS) and an SP-2560 column [21].…”

“…Use of capillary columns coated with 100 % cyanopropyl siloxane (CPS) is the current preferred approach for the separation of positional and geometric isomers of unsaturated FAME, specifically for trans FA [3,[16][17][18][19][20]. However, it is evident that isothermal elutions [17,19,21], single temperature programs [18,19], combinations of temperature programs [18] or use of a combination of results achieved using different GC columns [16,21] are unable to resolve all the FA present in marine [3,21] or ruminant lipids [16,18].…”

Asymmetric Synthesis of Methoxylated Ether Lipids: Total Synthesis of n-3 Polyunsaturated Docosahexaenoic Acid-Like Methoxylated Ether Lipid

“…It is the only routine method that enables the quantification of trans-isomer levels below 1% and is extensively used within the marine oil industry. 42 It is based on the use of highly polar extra-long capillary GC columns commonly with cyanopropyl-coated stationary phases. Reference samples for the trans-isomer GLC analysis are prepared by chemical isomerization of pure EPA or DHA with p-toluenesulfinic acid and the isomers fractionated by silver ion HPLC to get hold of pure fractions of mono-and ditrans-isomers.…”

Comparison of Separations of Fatty Acids from Fish Products Using a 30‐m Supelcowax‐10 and a 100‐m SP‐2560 Column

“…It is becoming evident that even a 100-m CPS by itself is limited in its capacity to resolve these FAME mixtures in a single analysis. Mjøs and Haugsgjerd [40] recently reported extensive overlap of FA common in fish oils with 16:1, 18:1, 18:2, and 18:3 isomers present in other fats. FAME were identified on the basis of the distinct differences in their electron impact mass spectra, but identification of minor and overlapping peaks by mass spectrometry was not possible [40].…”

“…Mjøs and Haugsgjerd [40] recently reported extensive overlap of FA common in fish oils with 16:1, 18:1, 18:2, and 18:3 isomers present in other fats. FAME were identified on the basis of the distinct differences in their electron impact mass spectra, but identification of minor and overlapping peaks by mass spectrometry was not possible [40]. There are numerous instances of such limitations in GC separations, indicating that mass spectrometric analysis and silver-ion separations will both be necessary to resolve these mixtures.…”