Quantitative Determination of IPA and DHA in the Refined Fish Oil by Capillary Gas Chromatography: Collaborative Study and Standardization

The authors developed a method for the quantitative determination of icosapentaenoic acid (IPA) and docosahexaenoic acid (DHA) in refined fish oil containing polyunsaturated fatty acids based on data obtained from a laboratory collaborative study. Three kinds of oils were (a) refined fish oil (labels specifying IPA content was 18%), (b) refined fish oil (labels specifying IPA content was 28%) and (c) mixture of (a) and (b) [50 : 50 (wt/wt)]. Methylation of triacylglyceride was carried out in a methanol solution of 2M potassium hydroxide. The tricosanoic acid methyl ester served as the internal standard for determining polyunsaturated fatty acid methyl esters by capillary gas chromatography. All data were analyzed statistically for determination of intra- and inter-laboratory variation. IPA and DHA values were consistent with intra- and inter-laboratory coefficients of variation less than 3%. The present method is thus shown suitable for determining IPA and DHA in refined fish oil containing polyunsaturated fatty acids in excess.