Capillary Column Gas Chromatographic Method for Analysis of Encapsulated Fish Oils and Fish Oil Ethyl Esters: Collaborative Study

Abstract

Abstract A gas chromatographic (GC) method using a capillary column for analysis of encapsulated fish oils and ethyl esters was studied collaboratively in 21 laboratories. Each collaborator analyzed 6 soft-gelatin encapsulated samples; 5 were trlacylglycerol oils (one was a blind duplicate), and one was an ethyl ester concentrate of omega-3 (n-3) polyunsaturates. Constituent fatty acids of the oils were converted to methyl esters by base-catalyzed transesterlflcatlon of the oils; any free acids in the oils were esterlfied by subsequent reaction with BF3/CH3OH. The ethyl ester concentrate required no further derlvatlzation. Results were reported as area percentages of 24 analytes of nutritional or biochemical interest. In addition, weights (mg/g sample) of EPA (all-c/s-5,8,11,14,17-elcosapentaenolc acid or 20:5n-3) and DHA (all-c/s- 4,7,10,13,16,19-docosahexaenoic acid or 22:6n-3) were determined through the use of the internal standards, respectively, methyl tricosanoate (23:0) and ethyl 23:0, for the methyl and ethyl esters. The only instrumentation specifically required was a flexible fused silica capillary GC column coated with a bonded polyglycol such as Carbowax-20M, an oxygen scrubber Installed In the carrier gas supply line, and a flame Ionization detector (FID). Most of the collaborators experienced little difficulty In applying the method, and, of 2526 values reported, only 4.3% were identified as outlier values. The reproducibility relative standard deviations (RSDR) compared favorably in most instances with, or were substantially better than, those of 2 earlier collaborative studies of fish oils. Because the variances were homogeneous, standard deviations and relative standard deviations determined on the area percent analyses of the blind duplicate oils were pooled to give the following mean values: sr = 0.15, RSDr = 4.88%, sR = 0.41, and RSDR = 12.91%. Analytes that rarely occur at greater than 0.5% In marine oils (22:0,22:4n-6,22:5n-6,24:0, and 24:1) were not Included in these calculations. The method was adopted first action by AOAC International as an American Oil Chemists' Society (AOCS)-AOAC method.