On-line sample preparation for the determination of riboflavin and flavin mononucleotides in foodstuffs.

An on-line sample preparation method is described for the determination of riboflavin and flavin mononucleotide (FMN) in milk and cereal samples by high-performance liquid chromatography (HPLC) with fluorescence detection. The on-line system consists of microwave extraction followed by dialysis and trace enrichment with a C18 mini-column. Sample preparation was minimal, with milk samples being directly introduced into the system and cereal only needing to be ground prior to analysis. Results were obtained for a range of samples and these were found to be in agreement with the Association of Official Analytical Chemists (AOAC) method and a previously reported HPLC method. Recoveries were between 94 and 106% for a range of different samples and the relative standard deviation for ten samples was in the range 1.2-2.0%. During the microwave extraction all the flavin adenine dinucleotide (FAD) was converted into FMN and 15% of FMN was converted into riboflavin. The full analysis time on the ground samples was about 20 min.