Evaporation‐free Supercritical Fluid Chromatography—Internal Standard Correction—Solvent Suppression—Quantitative Nuclear Magnetic Resonance for Chiral Separation and Quantification of Quinine

ABSTRACT Accurate quantification of structurally similar impurities in chiral drugs remains a critical challenge in pharmaceutical quality control. Herein, we established supercritical fluid chromatography—internal standard correction—solvent suppression—quantitative nuclear magnetic resonance (SFC—ISC—SS—qNMR) for the rapid and accurate purity assessment of low‐purity quinine (QN). Baseline separation of QN from its chiral isomer quinidine was achieved within 10 min using SFC. The collected eluate, without any nitrogen blowing or freeze‐drying, was directly mixed with an IS and a trace amount of deuterium oxide for 1 H qNMR analysis, reducing the total sample preparation time to less than 7 min. An excitation sculpting pulse sequence (zgesgp) was employed to effectively suppress the methanol solvent peak, yielding a flat baseline and an excellent signal‐to‐noise ratio (S/N > 5000:1). Internal standard correction based on SFC peak area ratios before and after purification eliminated losses and errors during sample preparation. Method validation showed that the determined purity of QN (95.40% ± 0.17%) was in agreement with results obtained by two independent direct qNMR strategies (95.61% ± 0.11% and 95.44% ± 0.23%). Compared with previously reported ISC—high‐performance liquid chromatography—qNMR and SFC—ISC—qNMR methods, the proposed approach significantly reduced the sample preparation time, completely avoided the nitrogen blowing or freeze‐drying steps, and achieved seamless hyphenation of SFC and qNMR. This strategy provides an efficient, green, and generalizable paradigm for the accurate quantification of low‐purity organic compounds in chiral drugs and complex matrices.