Restek
Resource Hub / ChromaBLOGraphy / EN 14103 on the Rtx-225 Separate cis trans FAMEs without co-eluting C190

EN 14103 on the Rtx-225 – Separate cis/trans FAMEs without co-eluting C19:0

3 Oct 2022

EN 14103 describes analytical methods for the determination of the ester content in fatty acid methyl esters (FAME) intended for incorporation into diesel fuel, with a specific measurement of linoleic methyl ester content. FAMEs with methyl esters between C6-C24, excluding linoleic acid methyl ester, are expected to comprise 90% mass fraction (m/m) of the methyl ester content, while methyl esters from linoleic acid methyl ester are expected to comprise 1-15% m/m.

In 2020, EN 14103 was updated to include a purity analysis of the internal standard, nonadecanoic acid methyl ester, using a separate GC column and method. Other updates include new calculations, results from an interlaboratory study, increased sample size, and specifics regarding chromatogram interpretation. The method recommends a high temperature column such as the Rxi-5HT (cat# 13906) for determining the purity of your nondecanoic acid methyl ester (cat# 35055) internal standard, and a polyethylene glycol phase column similar to a Stabilwax (cat# 10623) or FAMEWAX (cat# 10623) for separating FAMEs in your sample. The polyethylene glycol phase works best for applications where the cis- and trans- separations are not critical, but depending on the oils being used, it may be necessary to separate those cis- and trans- isomers. Luckily, the method does allow for alternative stationary phases to be used, provided it is adequately tested.

Unlike the Stabilwax, cyanopropyl phases are pretty good at separating cis- and trans- FAMEs. The cyanopropyl groups in the stationary phase can interact more easily with cis- double bonds in the FAME backbone (Figure 1), increasing retention of cis- isomers.

blog-EN-14103-on-the-RTX-225-01.png

Figure 1: Simplified interactions between cis- and trans- FAME isomers, and the Rtx-225 stationary phase

Comprised of 50% cyanopropylmethyl and 50% propylmethyl polysiloxane, the Rtx-225 (cat# 14023) may serve as your solution for separating cis- and trans- isomers during your EN 14103 analyses. Despite cautionary notes in EN 14103 about cyano-phase columns, the Rtx-225 separates linoleic acid and nonadecanoic acid methyl esters (Figure 2). Nonadecanoic acid methyl ester has been added to the Rtx-225’s ProEZGC FAME library, so you can see if the Rtx-225 is the right column for your EN 14103 analyses. Adjust oven and column parameters to improve separations without running samples.

blog-EN-14103-on-the-RTX-225-02.png

Figure 2: (GC22_FF1379) Separation of cis/trans FAME Mix (cat# 35079) and nondecanoic acid methyl ester cat# 35055 on the Rtx-225 using conditions recommended in EN 14103.