Novel spectrophotometric method for the determination of paclitaxel through complex formation with osmium

Paclitaxel (Pac) is an important anticancer bioactive compound, and the availability of an accurate and robust analytical method for its quantification is of utmost importance. In this investigation, a novel, direct, and reliable spectrophotometric method has been proposed for the estimation of Pac via a complex formation reaction with osmium (Os). The method was based on the reaction of Pac with Os tetroxide, which produced a yellowish-brown complex. The resulting complex is soluble in water and displays a maximum absorption peak at 482 nm. The reaction conditions, including reactant concentration, pH, temperature, and reaction time, were optimized to obtain the best spectrophotometric response. A thorough method validation study was conducted, demonstrating that the calibration curve is linear over the concentration range of 1.0-55 μg/mL and follows Beer's law, with a molar absorptivity of 3.01 × 10^-4 L/mol^-1.cm^-1. The limit of detection (LOD) and limit of quantitation (LOQ) were 0.0098 and 0.0328 μg/mL, respectively. The recovery values were planned and found to be 98.70%-100.23%. At the same time, the precision values (represented by relative standard deviation percent [RSD%]) were better than 0.81% (in injections) and 1.859% (in biological fluids), depending on the Pac concentration. The suggested method was successfully applied to estimate Pac in a pharmaceutical formulation (as injections) and in spiked biological fluids (serum and urine), with results showing good accuracy and precision compared to the reference method.