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Now you will focus on the methods to determine the fatty acid profile of a food (in this case margarine). At the end of this part you will finalize your database.

Stationary phases and resolution problems

The liquid stationary phase in both packed columns and capillary columns can have different separation properties. Roughly 3 types of stationary phases are used: high polarity phases, medium polarity phases and apolair phases. Each type of stationary phase has different separation characteristics. Here you see an overview of the important characteristics (limitations) with respect to the power to separate fatty acids.

• Packed column with apolar or medium polar stationary phase:
- Poor resolution of saturated and unsaturated fatty acids of the same chain length.

• Packed column with polar stationary phase:
- Incomplete separations of geometrical isomers (cis/trans fatty acids)
- Separations of positional isomers [(n-3), (n-6) fatty acids] may be inadequate
- Co-elution of fatty acids (FA) with different chain lengths may occur

• Capillary column with medium polar stationary phase:
Far better separation than corresponding packed columns, however
- No separation of cis/trans isomers

• Capillary column with high polar stationary phase:
- Improved separation of positional [n-3, n-6, n-9] isomers and geometrical isomers (cis/trans), but still no complete cis/trans separation
- Resolution problems in separation of very long chain polyunsaturated cis/trans isomers (margarines containing partially hydrogenated fish oils)
For the separation of fatty acids in samples containing no geometrical isomers, capillary columns with medium polar stationary phases can best be used. For the separation of fatty acids in samples containing geometric (cis/trans) isomers, capillary columns with a highly polar stationary phase can best be used.