Factorial design and response surface optimization of spectrophotometric sequential injection analysis of olanzapine formulations

A new spectrophotometric sequential injection analysis (SIA) method for the assay of olanzapine in pharmaceutical formulations was optimized by the factorial design and the response surface approaches. The method was based on the oxidation of olanzapine by an excess amount of permanganate in sulfuric acid media. The reduction of permanganate was spectrophotometrically detected at 570 nm. The 2³ full factorial design was adopted for the optimization of permanganate concentration, sulfuric acid concentration and flow rate. The method was validated based on the IUPAC guidelines. Real pharmaceutical samples were subjected to the proposed SIA method and the results were in satisfactory agreement with those obtained by a previous spectrophotometric method. The full-automation of SIA empowered the proposed method with high repeatability (RSD 1.74%, n = 7) and intermediate-precision (RSD 2.53%, n = 5). Additionally, both automation and miniaturization offered high sampling frequency (26 samples/h). Furthermore, the employment of chemometric optimization enhanced sensitivity of the method with limits of detection and quantification of 1.07 and 3.57 mg/L, respectively. Comparing with previous olanzapine assay methods, which employing conventional analytical techniques, the new SIA method is inexpensive in terms of instrumentation, consumption of reagents and samples as well as effort and manpower. The SIA method is also safer for handling solutions and for the environment.