Flavin mononucleotide for indirect laser-induced fluorescence detection of anions separated by capillary electrophoresis

Abstract

Flavin mononucleotide (FMN), also known as riboflavin-5′-phosphate, has been characterized as an indirect laser-induced fluorescence (LIF) detection reagent for inorganic anions, organic acids, anionic surfactants and polyphosphates after separation by capillary electrophoresis (CE). FMN provides a good wavelength match for laser excitation at 488 nm, is readily soluble in aqueous or aqueous/organic solutions, and unlike fluorescein provides strong fluorescence at both acidic and basic pH values. Analyte peaks due to a loss in FMN fluorescence are generated at weakly alkaline pH values as expected, but peak direction is switched at more alkaline pH values such as 8.6 or 9.0. A separation of 21 inorganic anions and organic acids is possible in about 20 min using the indirect LIF mode using 10 μ M FMN with 2 m M diethylenetriamine as the electroosmotic flow suppressor. Detection limits for these analytes are in the 10–20-μg/l range without any required preconcentration. The use of methanol improves resolution and facilitates the simultaneous separation of aliphatic/aromatic surfactant standard mixtures or commercial shampoos in less than 20 min.