Background: In borax buffer, ephedrine (EPH) and pseudoephedrine (PSE) can be well separated (Rs>10) in capillary electrophoresis (CE) without adding any other compounds, but the specific mechanism remains unclear. Methods: Titration analysis, nuclear magnetic resonance analysis, mass spectrum analysis and molecular modeling were used to investigate the separation mechanism. Results: Tetrahydroxy borate (a hydrolyzate of borax or boric acid) could react with ephedrine and pseudoephedrine to form self-assembled complexes, but the two complexes had different stabilities and electrophoretic mobilities resulting from the different steric configurations of analytes. Conclusion: The complexation based on borax was responsible for the separation.

中文翻译：

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毛细管电泳分离硼砂缓冲液中麻黄碱和伪麻黄碱的机理研究

背景：在硼砂缓冲液中，麻黄碱（EPH）和伪麻黄碱（PSE）在毛细管电泳（CE）中可以很好地分离（Rs>10），无需添加任何其他化合物，但具体机制仍不清楚。方法：采用滴定分析、核磁共振分析、质谱分析和分子模型研究分离机理。结果：四羟基硼酸盐（硼砂或硼酸的水解产物）可以与麻黄碱和伪麻黄碱反应形成自组装复合物，但由于分析物的空间构型不同，导致两种复合物具有不同的稳定性和电泳迁移率。结论：基于硼砂的络合是分离的原因。