GC Analyses of Free Fatty Acids

Introduction

One area of current public interest is nutrition, specifically, the fat content of food. Obesity, diabetes, and cardiovascular disease, along with their related complications, are increasing in America, Europe, and in other parts of the world. However, it is not only total fat, but also the type of fat that must be considered. Some ‘good fats’ are required for biochemical processes or necessary for dissolving fat-soluble vitamins. Other ‘bad fats’ accumulate in the cardiovascular system, potentially leading to health problems.

Each type of fat has unique physical (such as boiling point) and chemical (such as degree, location, and configuration of unsaturation) properties. Because of this, different analytical methods are required to properly obtain all desired information to be of use in determining the nutritional and health value of a food.

Another article in this Reporter covers the analysis of FAMEs by boiling point elution (1). Previous Reporter articles have detailed the GC analysis of omega 3 and omega 6 fatty acids as FAMEs and cis/trans fatty acid isomers as FAMEs (2-3). This article will discuss the analysis of free fatty acid.

Free Fatty Acids

Short chain, volatile fatty acids are typically analyzed in the free form using specialized columns. This group of compounds may be referred to as free fatty acids (FFAs), volatile fatty acids (VFA), or carboxylic acids. The analysis of fatty acids in the free form instead of as fatty acid methyl esters results in easier and quicker sample preparation. Additionally, artifact formation that may result from a derivatization procedure, is eliminated.

GC Column Choices

For the GC analysis of free fatty acids, a specialized column that will not allow the adsorption of active carboxyl groups is required. The Nukol™, with its acidic character, is well suited for this application, allowing chromatography with excellent peak shapes.

Column Specifications for the Nukol™:

• Application: The incorporation of acid functional groups into the phase lends an acidic character to this column, useful for analyses of volatile acidic compounds. Difficult to analyze carboxylic acids (free fatty aClds) can be analyzed with excellent peak shape and minimal adsorption.
• USP Code: This column meets USP G25 and G35 requirements.
  
• Polymer: Bonded; acid-modified poly(ethylene glycol)
  
• Temperature Limits: 60 °C to 200/220 °C
  

Figures 1-3 show chromatograms of various free fatty acid mixes on several dimensions of the Nukol, using both isothermal and oven temperature programmed run conditions. Fatty acid chain lengths in these three analyses range from C2-C20. As shown, excellent peak shapes are observed for all analytes.

Chemical Standards

Standards for the determination of free fatty acids should be purchased from a chemical manufacturer with knowledge in the preparation, handling, storage, and shipment of volatile analytes. Supelco, with over 40 years in chemical standard manufacturing, offers several suitable standards. Selected standards can be found in the product listing at the end of this article.

Conclusion

Measuring and reporting of the fatty acid content of food is an important step that allows consumers the chance to establish a healthy dietary strategy. Nukol capillary GC columns and specially formulated chemical standards are quite suitable for the application shown in this article, GC analyses of free fatty acids.

This article, those in previous Reporters, and the sigma-aldrich.com/fame web page illustrate the breadth of specialized GC columns and the vast array of specially formulated chemical standards that are available for fatty acid and FAME analyses. Sigma-Aldrich/Supelco, with unsurpassed knowledge and product offerings, is truly the total solution for obtaining superior products for the GC analyses of fatty acids from foods for nutritional needs.