INTERCOMPARISON OF METHODS FOR THE DETERMINATION OF VITAMINS IN FOODS .1. FAT-SOLUBLE VITAMINS

An intercomparison of methods involving 18 European laboratories was organized to assess the state-of-the-art of vitamin determination in foods. Each laboratory received identical samples of dry food reference material (homogeneous powders, milk powder, pork muscle and haricot vert beans), which were recently certified for major dietary components and elements. Each laboratory was requested to perform the analyses by its own methods. Results for fat-soluble vitamins are reported. All participants isolated the fat-soluble vitamins by alkaline saponification. For retinol, only high-performance liquid chromatography (HPLC), reversed- or normal-phase, was applied, with both ultraviolet (UV) and fluorescence detection. Results in milk powder showed a relative standard deviation of reproducibility (RSD(Reprod)) of only 10%. Carotene was determined by HPLC (reversed- and normal-phase) and with open-column chromatography at atmospheric pressure. For beta-carotene results in milk powder agreed very well; the RSD(Reprod) was 14%. The values reported for haricot vert beans showed poor agreement; the RSD(Reprod) was 52%. A major part of this variability was due to differences in methodological principles. The results for alpha-tocopherol in milk powder and haricot vert beans agreed very well, with RSDs(Reprod) of 16 and 15%, respectively. Only HPLC (reversed- and normal-phase) with UV and fluorescence detection was applied.