Micellar liquid chromatography determination of B vitamins with direct injection and ultraviolet absorbance detection

A micellar reversed-phase liquid chromatographic procedure was developed for the control of five water-soluble vitamins, B (nicotinamide), B1 (thiamine), B2 (riboflavin), B6 (pyridoxine and pyridoxamine), in multivitamin pharmaceutical formulations (capsules, pills and syrups). Optimization procedure includes studies about the composition of the mobile phase (sodium dodecyl sulphate and the modifiers propanol, butanol or pentanol), flow-rate and temperature. Chromatographic analysis of all vitamins was carried out using a single mobile phase of 0.1 M SDS-4% (v/v) pentanol at pH 3, in a C18 column in isocratic mode, and UV-detection at 270, 290 and 325 nm. The flow-rates selected were 1.0 ml/min in the interval 0 to 6 min, and 2.0 ml/min until the end of the chromatogram and temperature was 45 degrees C. In the micellar liquid chromatographic system, the samples were injected without pretreatment, and the analysis time was below 12 min. Repeatabilities and intermediate precision were achieved according to ICH, and were below 5%. When the method is applied to real samples, the amount found with respect to the declared compositions were within the 91-105% range. These results were similar to those obtained with a conventional 60:40 (v/v) methanol-water mixture for some of the vitamins, but with the advantage of use a single mobile phase for the analyses of the five vitamins, with direct injection of the samples and reduced toxicity, flammability, environmental impact and cost of the micellar-pentanol solutions.