Quality by design approach for enantioseparation of terbutaline and its sulfate conjugate metabolite for bioanalytical application using supercritical fluid chromatography

Terbutaline is mainly metabolized by sulfoconjugation stereoselectively, favoring its (S)-(+) enantiomer. Reported chiral separations of Terbutaline enantiomers were achieved by various chromatographic methods. However, the simultaneous enantioseparation of Terbutaline and the monosulfate conjugate metabolites was never reported. This study aims at shedding light on the influential factors and interactions leading to successful enantioseparation of Terbutaline and its monosulfate conjugate pairs by Supercritical Fluid Chromatography (SFC) for the first time within a Quality by Design framework using Design of Experiments. The effect of molarity of mobile phase additive, mobile phase flow rate, column temperature and back pressure were evaluated. Compared to previous reports, the response surface interestingly revealed the favorability of high temperature and high flow rate up to 2.25 ml/min for resolution of the two pairs of enantiomers on polysaccharide chiral stationary phase CHIRALPAK IC. In addition, a switch in the elution order of Terbutaline and the sulfate conjugate peak pairs was observed upon elimination of the mobile phase additive where the sulfate conjugate underwent intra-molecular ionic interactions and the change in elution order was only due to TER behavior. The multifactorial interactions would not have been detected with the common one-factor-at-a-time approach during method development, demonstrating the superiority and importance of the Analytical Quality by Design frame in enantioseparation.