ONLINE SAMPLE PREPARATION FOR THE DETERMINATION OF RIBOFLAVIN AND FLAVIN MONONUCLEOTIDES IN FOODSTUFFS

An on-line sample preparation method is described for the determinatio n of riboflavin and flavin mononucleotide (FMN) in milk and cereal sam ples by high-performance liquid chromatography (HPLC) with fluorescenc e detection. The on-line system consists of microwave extraction follo wed by dialysis and trace enrichment with a C-18 mini-column. Sample p reparation was minimal, with milk samples being directly introduced in to 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 b e in agreement with the Association of Official Analytical Chemists (A OAC) method and a previously reported HPLC method. Recoveries were bet ween 94 and 106% for a range of different samples and the relative sta ndard deviation for ten samples was in the range 1.2-2.0%. During th;e microwave extraction all the flavin adenine dinucleotide (FAD) was co nverted into FMN and 15% of FMN was converted into riboflavin. The ful l analysis time on the ground samples was about 20 min.