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

An intercomparison of methods involving 18 European laboratories was o rganized to assess the state-of-the-art of vitamin determination in fo ods. Each laboratory received identical samples of dry food reference material (homogeneous powders, milk powder, pork muscle and haricot ve rt 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 p articipants isolated the fat-soluble vitamins by alkaline saponificati on. For retinol, only high-performance liquid chromatography (HPLC), r eversed- or normal-phase, was applied, with both ultraviolet (UV) and fluorescence detection. Results in milk powder showed a relative stand ard deviation of reproducibility (RSD(Reprod)) of only 10%. Carotene w as determined by HPLC (reversed- and normal-phase) and with open-colum n chromatography at atmospheric pressure. For beta-carotene results in milk powder agreed very well; the RSD(Reprod) was 14%. The values rep orted for haricot vert beans showed poor agreement; the RSD(Reprod) wa s 52%. A major part of this variability was due to differences in meth odological 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.