Rapid and selective determination of pitavastatin calcium in presence of its degradation products and co-formulated drug by first-derivative micelle-enhanced and synchronous fluorimetric methods
New spectrofluorimetric methods are presented for the rapid and selective determination of pitavastatin calcium (PIT) in the presence of its hydrolytic degradation products and the co-formulated drug ezetimibe (EZE). In the first method (method A), PIT was determined in the presence of its hydrolytic degradation products by measuring the first derivative (1D) of its enhanced native fluorescence using sodium dodecyl sulfate (SDS) as an anionic micelle enhancer at a pH of 4.1, which was adjusted using Britton–Robinson buffer in aqueous media. PIT was subjected to stress conditions of 5 M hydrochloric acid and 5 M sodium hydroxide. The 1D peak amplitude was measured at a λem of 415 nm using a λex of 252 nm. The effect of different surfactants on the fluorescence of PIT was studied; the quantum yield of PIT was in the following order: SDS (0.30) > cetrimide (0.23) > Tween (0.02). A second method (method B) was developed for the simultaneous determination of PIT and the co-formulated drug EZE in the presence of degradation products of PIT. This method utilized synchronous fluorescence spectroscopy (SFS) in an acetonitrile medium. The wavelengths that were used were λex = 260 nm and λem = 330 and 272 nm for PIT and EZE, respectively, using Δλ = 40 nm. Validation of the proposed methods was performed according to the ICH guidelines. The methods were employed for the determination of PIT (methods A and B) and EZE (method B) in bulk powder, pharmaceutical preparations of co-formulated drug substances and laboratory-prepared mixtures containing hydrolytic degradation products of PIT. Statistical analysis proved that the investigated assays were excellent. It was concluded that method A was inexpensive and environmentally friendly.