Chromatographic fingerprint based on serially coupled columns combined with multiple-component quantitation with a single reference standard for quality evaluation of Shen–Zhi–Ling oral liquid

Conventional liquid chromatographic fingerprint methods with a single column lack enough selectivity and separation power for analyzing complex samples with a wide range of polarities. In this work, an HPLC fingerprint method based on the serial coupling of two columns was developed to evaluate the quality of Shen–Zhi–Ling oral liquid. Twelve batches of Shen–Zhi–Ling oral liquid were used to carry out the fingerprint analysis. Compared to 22 common peaks achieved in the fingerprint with a single column, 29 common peaks were obtained when using the serial coupling of two columns under the same conditions. Five components including albiflorin, paeoniflorin, liquiritin, cinnamic acid, and glycyrrhizic acid ammonium salt were simultaneously determined with paeoniflorin as the reference standard. The established method was validated in terms of specificity, linearity, precision, accuracy, stability, and robustness. Then the five components in 12 batches of products were successfully determined. Compared with the external standard method, the determination results showed no remarkable differences. In addition, similarity analysis and hierarchical clustering analysis combined with heatmaps were also employed to perform quality assessment. The fingerprint based on directly connecting two columns in series combined with multi-component quantitation with a single reference standard could provide a feasible and attractive approach to evaluate the quality of Shen–Zhi–Ling oral liquid.