Intercomparison of methods for the determination of vitamins in foods. Part 2. Water-soluble vitamins

Abstract

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 have recently been certified for major dietary components and elements. Each laboratory was requested to perform the analyses 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-performance liquid chromatography (HPLC), fluorimetric and microbiological methods 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 microbiological 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 high, except in milk powder. The RSD_Reprod ranged from 18 to 51%. A major 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 obtained with the microbiological methods in milk powder, pork muscle and haricot vert beans, was small; RSD_Reprod= 9–15%. The variation in the results reported for vitamin C in haricot vert beans was high, with an RSD_Reprod of 15% Participants used HPLC, fluorimetry and indophenol titration.