DEFINITION
This method provides a gas–liquid chromatography (GLC) procedure for the determination of the fatty acid composi-tion of marine oils and other oils containing long chain polyunsaturated fatty acids (PUFAs). The fatty acid methyl esters (FAMEs) of the sample are separated on a capillary gas chromatography column having a polar stationary phase, according to their chain length (CL), degree of unsaturation, and double bond position (i.e., positional isomers). This method, however, is not suitable for separation of cis and trans isomers of unsaturated FAMEs.

SCOPE
This method determines the content and concentrations of saturated fatty acids (SFA), cis-monounsaturated fatty acids (MUFA), and cis-polyunsaturated fatty acids (PUFA), including arachidonic acid (ArA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), in marine oils and other oils such as single cell oils (SCOs) using capillary GLC. For nutritional labeling purposes the total fat, saturated, cis-monounsaturated, and cis-polyunsaturated fatty acid contents are to be determined with this method. This method is not suitable for determining the trans fatty acid composition of hydrogenated marine oils or other oils containing long chain polyunsaturated fatty acids. AOCS Ce 1h-05 or Ce 1j-07 are the methods of choice for quantitating and separating oils with trans fatty acids, and short chain fatty acids (= 10 carbons) should be quantitated with AOCS Ce 1j-07.

This method utilizes a triacylglycerol (23:0 TAG) internal standard (IS) for determining the concentration of the individual FAMEs in the oil samples after methylation. This method may also be used with marine oil fatty acid ethyl esters (FAEEs). FAEEs are methylated to their corresponding FAMEs. This conversion allows for ease of interpretation and quantitation for determining the fat and fatty acid contents plus the conversion of any residual acylglycerols, such as triacylglycerols (TAGs) to FAME. FAEEs should not be analyzed without derivatization since nutritional labeling requires all fatty acids to be quantitated as FAME.
Theoretical Correction Factors (TCFs) are used to quantitate all saturated and monounsaturated fatty acids greater than or equal to 12:0 and polyunsaturated fatty acids (PUFA) of 18 carbons. TCFs are also used for fatty acids, which lack standards, such as 6c, 9c, 12c, 15c, 18c-21:5 (21:5n-3). Empirical Correction Factors (ECFs) are used for long chain PUFA of 20 carbons or more and three or more double bonds for which standards are readily available. Very long chain fatty acids (VLC FAs) may be present in SCOs and certain marine fats and oils. VLC FAs (25:0 and greater) require a longer run time with a pressure flow ramp for elution. Phthalate esters are also known to be present in marine oils and therefore their retention times are noted in Tables 1 and 2, however, their identification is not required for fatty acid or nutritional labeling purposes.