INTERCOMPARISON OF METHODS FOR THE DETERMINATION OF VITAMINS IN FOODS.2. WATER-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 have recently been certified for major dietary compon ents and elements. Each laboratory was requested to perform the analys es by its own routine methods. The results for water-soluble vitamins are reported. The reproducibility for the determination of vitamin B1 in milk powder, pork muscle and haricot vert beans with high-performan ce liquid chromatography (HPLC), fluorimetric and microbiological meth ods was good, with the relative standard deviation of reproducibility (RSD(Reprod)) ranging from 11 to 18%. Differences between laboratories for the determination of the vitamin B2 content of milk powder, pork muscle and haricot vert beans determined using HPLC and microbiologica l methods were very high, with RSD(Reprod) ranging from 28 to 74%. The extraction and hydrolysis procedures were probably the most important sources of variation. For vitamin B6 various HPLC and microbiological methods were used. The variation in the results for vitamin B6 was hi gh, except in milk powder. The RSD(Reprod) ranged from 18 to 51%. A ma jor part of this variability was due to differences in the extraction and hydrolysis procedures and problems with the identification of the vitamin B6 vitamers by HPLC. Variation in the results for niacin obtai ned with the microbiological methods in milk powder, pork muscle and h aricot vert beans, was small; RSD(Reprod) = 9-15%. The variation in th e results reported for vitamin C in haricot vert beans was high, with an RSD(Reprod) of 15%. Participants used HPLC, fluorimetry and indophe nol titration.