New methods for analysing fatty acids in foods

Agilent Technologies Europe has announced two improved methods for identifying fatty acids in foods.

Fatty acids can be isolated from most foods, especially from edible fats and oils derived from agricultural products such as corn, maize, olives, and soybeans.

Fatty acid analysis is preceded by saponification of the glycerols and derivitisation to the fatty acid methyl esters (Fames).

Fames are normally analysed by gas chromatography (GC) or GC/mass spectrometry (GC/MS) on columns coated with polar stationary phases.

Chemists from Agilent Technologies, the Research Institute for Chromatography in Kortrijk, Belgium, and the University of Gent in Gent, Belgium, have developed two retention time locking (RTL) methods for analysing Fames.

RTL offers easy peak identification and simple comparison of data from different GCs and different laboratories.

The choice between the two methods depends on sample complexity and the degree of fatty acid characterisation required.

The first method uses a DB-WAX column that separates Fames according to carbon number (from C4 to C24) and fatty acid saturation.

This method uses a gas chromatograph with flame ionisation detector or mass spectrometer (GC/MS).

The DB-WAX column does not separate cis and trans isomers, and for complex mixtures such as fish oils, does not resolve some Fames.

However, this column is sufficient for most classical oil and fat characterisations.

In addition, it can be used to characterise some animal fats such as butyric acid in milk fat, which is important in milk and dairy analysis and in the analysis of chocolate products.

The second method uses the same instruments as the first method but with a DB-23 cyanopropyl column.

This method is appropriate for analysing more complex samples such as fish oils, hydrogenated fats and cis and trans isomers.

Both methods use RTL, which allows analysts to obtain virtually identical retention times on any gas chromatograph, independent of inlet, injection technique or detector.

This makes peak identification more accurate and allows easy correlation of results between instruments.

Agilent's published retention time database, which is available at no charge from its website, enables rapid and reliable Fame identification.

An additional benefit of RTL is that retention times in the calibration table remain unchanged, even after column maintenance or change.

For GC/MS, an available spectral library can screen data files using spectra in combination with their locked retention times.

For further information, request application note 'Improving the Analysis of Fatty Acid Methyl Esters Using Retention Time Locked Methods and Retention Time Databases,' Agilent publication number 5988-5871EN.

This note is available without charge from any Agilent sales office or its website (see link above).