Rapid Supercritical Fluid Chromatography Method for Separation of Chlorthalidone Enantiomers

Abstract

Supercritical fluid chromatography employing chiral stationary phases is a popular separation technique to perform enantioselective separations. The main advantages of supercritical fluid chromatography are low analysis time, low consumption of organic modifiers, and therefore lower costs and higher environmental friendliness. A novel method for the separation of chlorthalidone enantiomers, widely used diuretic drug, is reported that clearly demonstrates the advantages of supercritical fluid chromatography. The effects of the amount and type of organic modifiers, temperature, and back pressure on enantioselectivity and resolution of the enantiomers were evaluated. The baseline separation was achieved in less than 2.5 min in the optimized system composed of Chiralpak AD column, mobile phase CO₂/MeOH 50/50 (v/v), temperature 40°C, a flow rate of 4.0 mL/min, and 120 bar back pressure. Moreover, enantiomers of chlorthalidone were determined in two commercially available pharmaceuticals. The proposed method may be easily transferred to a semi-preparative scale.

Keywords:

• Chiral separation
• Chlorthalidone
• Saccharide based chiral stationary phase
• SFC

Acknowledgments

The authors have declared no conflict of interest.

The Grant Agency of the Charles University in Prague, project No. 356411; the Ministry of Education, Youth, and Sports of the Czech Republic, project KONTAKT LH11018; and the long-term project MSM0021620857 are gratefully acknowledged for financial support. Prof. M. Schmid from the Department of Pharmaceutical Chemistry, University of Graz, is thanked for his generous gift of chlorthalidone. Furthermore, Prof. Ch. Roussel and Dr. N. Vanthuyne from the Chirosciences team of Aix-Marseille University are thanked for their kind help during the SFC experiments. The international cooperation between Charles University in Prague and Aix-Marseille University was established in the frame of the LPP - ERASMUS PROGRAMME.

Notes

Note: Chiralpak AD column, mobile phase CO₂/MeOH 50/50 (v/v), flow 4 mL/min, 40°C for the pressure measurements, 120 bar for the temperature measurements. α, enantioselectivity; Rs, resolution.

ACN, acetonitrile; CD, cyclodextrin; DEA, diethylamine; HAc, acetic acid; hex, n-hexane; hept, n-heptane; TEA, triethylamine; TEAA, triethylammonium acetate buffer; TFA, trifluoroacetic acid; - the chromatographic parameter was not available.

Note: k, retention factor; c, concentration; α, enantioselectivity.

A, peak area; H, peak height; E₁, first eluted enantiomer; E₂, second eluted enantiomer; α, enantioselectivity.