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The analysis of free riboflavin (RF) and its two coenzymes, flavin mononucleotide (FMN) and flavin-adenine dinucleotide (FAD), is optimized using reversed phase liquid chromatography with fluorescence detection. The stationary phase was amide-based and endcapped with trimethylsilyl, and the isocratic mobile phase consisted of a 10:90 v/v acetonitrile/phosphate buffer (pH 5). Peaks were identified by the retention characteristics and fluorescence spectra. Detection limits were 0.03, 0.05, and 0.24 ng for RF, FMN, and FAD, respectively. The vitamins were extracted using acetonitrile and the phosphate buffer. The procedure was applied to the determination of B2 vitamers in different types of food such as milk and soy-based infant formulas, beer, fruit juices, and honey of different types. Most B2 vitamin appeared as RF, while the coenzymes were present in lower amounts. The method was validated using two certified reference materials, and results within the certified range were obtained.

A flow injection-fluorimetric procedure for the determination of ranitidine is proposed. The assay is based on the reaction of the drug with sodium hypochlorite, to produce a primary amine, which reacts with o-phthalaldehyde and 2-mercaptoethanol to form highly fluorescent derivatives. The calibration graph, based on peak area, is linear in the range 20-500 ng ml-l of ranitidine with an accuracy of 3.4%. The corresponding detection limit is 13 ng ml-l (3.7 pmol). The method was applied to the determination of ranitidine in pharmaceuticals. The recovery was quantitative and no interferences from excipients were observed.