Facile and Sensitive Determination of Selenium (IV) in Pharmaceutical Formulations by Flow Injection Spectrophotometry

An automated flow injection spectrophotometric method has been developed for the rapid, simple, selective, and sensitive determination of selenium (IV) from various pharmaceutical multivitamin and mineral formulations. The method was based on the oxidation of 4-aminoantipyrine (4-amino-1,2-dihydro-1,5-dimethyl-2-phenyl-3H-pyrazole-3-one; 4-AAP) by selenium in presence of acidic medium and the coupling with N-(naphthalen-1-yl)ethane-1,2-diamine dihydrochloride (NEDA) to give a violet color derivative. Gilson P2 mini pulse peristaltic pump has been used for introducing the selenium (IV), dilute HCl, 4-AAP and NEDA solutions into reaction coil by an automatic system. The absorbance of the 4-AAP-NEDA color derivative was measured at 563 nm after a reaction time of 3 min in stop flow of 4-AAP-NEDA. Beer's law was obeyed for selenium in the concentration range 0.05–5.0 µg mL−1 and Sandell's sensitivity was found to be 0.00286 µg cm2. The performance of the present method was compared with the official method in terms of Student's F- and t-tests, and no significant difference was observed. This method was found to be suitable for estimating the selenium (IV) concentration in various pharmaceutical multivitamin and mineral formulations such as tablets and capsules.