A mathematical model of chromatographic retention of barbiturates in ion-pair reversed-phase chromatography

The chromatographic characteristics of barbiturates are studied by ion-pair reversed-phase HPLC. For some barbiturates, the dependence of the capacity factor on the concentrations of an ion-pair reagent and an organic modifier is modeled by a second-order two-factor rotatable experimental design. The empirical second-order regression equations show that the dependence of the retention volume on the main factors exhibits an extremum, a fact indicative of a marked curvature of the response surfaces. The quasi-stationary region of the response surface is examined.