Optimized Box-Behnken experimental design based response surface methodology and Youden's robustness test to develop and validate methods to determine nateglinide using kinetic spectrophotometry.

Selective and straightforward kinetic spectrophotometric methods were developed to quantify nateglinide (NTG) in pharmaceutical dosage forms. Fixed time (ΔA) and the equilibrium methods utilized the reaction of NTG with 1-chloro-2,4-dinitrobenzene (CDNB) in dimethyl sulfoxide (DMSO) with heating at 80 °C for 25 min to form a stable yellow-coloured Meisenheimer complex, which absorbs maximally at 421 nm. The optimization was achieved by utilizing the Box-Behnken experimental design (BBD) combined with response surface methodology (RSM). In which three significant factors were studied, namely, CDNB volume (A), heating temperature (B) and heating time (C) against the absorbance as a response. Method validation presented the International Conference on Harmonisation (ICH) parameters such as specificity, selectivity, linearity, precision, accuracy, limit of detection (LOD), limit of quantitation (LOQ), robustness and solution stability. The LOD and LOQ values were 0.48, 1.46, and 0.21, 0.62 µg/ml, respectively, for a fixed time (ΔA) and equilibrium methods with the linear dynamic range of 1-15 µg/ml. Furthermore, Youden's robustness test using factorial combinations of the selected analytical parameters was performed and investigated its influence with alternative conditions. All results were reproducible and quickly adopted for routine analysis of NTG in pharmaceutical formulations and laboratory preparations.