analytical method development and validation for a fixed-dose als combination using rp-hplc: a qbd and response surface optimization approach

This study presents the development and optimization of a robust and reliable rp-hplc method for the simultaneous estimation of sodium phenylbutyrate and taurursodiol in a fixed-dose combination, guided by quality by design (qbd) principles. sodium phenylbutyrate, an ammonia scavenger, and taurursodiol, a cytoprotective bile acid derivative, are used to treat neurodegenerative disorders such as als. a central composite design (ccd) was employed to systematically evaluate the effects of acetonitrile ratio and flow rate on three critical responses: resolution between peaks (r1), tailing factor of sodium phenylbutyrate (r2), and turursodiol (r3). the method was optimized using a waters x-bridge phenyl column with a mobile phase of acetonitrile: 0.1% orthophosphoric acid (opa) (30:70), a flow rate of 1.0 ml/min, and detection at 287 nm. the method exhibited excellent linearity (r² > 0.999), precision (%rsd < 1%), and accuracy (recovery: 98-102%). forced degradation studies confirmed its stability indicating capability. the optimized chromatographic conditions ensured high resolution and minimal tailing with satisfactory system suitability. this validated method provides a scientific basis for the quality control and routine analysis of neuroprotective agents in pharmaceutical formulations.