Institute for Infectious Diseases, University of Bern, Bern, Switzerland.
J Chromatogr A. 2022 Jun 21;1673:463087. doi: 10.1016/j.chroma.2022.463087. Epub 2022 Apr 22.
The impact of the two essential parameters, the complexation constant and the mobility of the formed diastereomeric complex, on stereoisomer separation in presence of a neutral chiral selector was assessed by computer simulation for an electrokinetic chromatography configuration with a uniform background electrolyte and one with a cationic discontinues buffer system of isotachophoretic nature. With two enantiomers of norpseudoephedrine as model analytes, data for seven cases featuring complexation in free solution with various combinations of input values, complexation with an immobilized selector and no complexation were analyzed in a hitherto unexplored way. For the uniform buffer study, the determined differences of the effective mobilities and separation selectivities of the stereoisomers were found to be equal to those calculated with the well-known algebraic equations. For the isotachophoretic system with its Kohlrausch adjusted zones, separation is also based on differences in effective mobilities, but the mobility differences cannot be predicted with the same algebraic equation. In both techniques, chiral separations occur due to the presence of the selector and if there is inequality between the mobilities of the transient diastereomeric complexes and the mobility of the free, uncomplexed analyte. Separation of the stereoisomers is possible when complexation constants, complex mobilities or both of these parameters differ. In the isotachophoretic separation a migrating steady-state is formed in which analytes either establish consecutive zones with plateau concentrations or, if present in an insufficient amount, as a peak-like distribution that migrates within a moving steady-state boundary. Simulation data illustrate for the first time the use of a spacer compound that establishes an isotachophoretic zone between enantiomers and thereby provides complete separation of the enantiomers and the possibility of individual detection in peak-mode isotachophoresis. They demonstrate that such an approach could be employed to assess the enantiomeric purity of a chiral compound.
采用计算机模拟的方法，评估了两个基本参数，即形成的非对映异构体复合物的络合常数和迁移率，对中性手性选择剂存在下立体异构体分离的影响。以降伪麻黄碱的两种对映体为模型分析物，用七种不同的输入值组合，在自由溶液中络合、与固定化选择剂络合以及不络合的情况下，对尚未研究过的数据进行了分析。在均匀缓冲液研究中，确定的立体异构体有效迁移率和分离选择性的差异与用著名的代数方程计算出的差异相等。对于具有 Kohlrausch 调整区的等速电泳系统，分离也是基于有效迁移率的差异，但不能用相同的代数方程预测迁移率的差异。在这两种技术中，手性分离是由于选择剂的存在，如果瞬态非对映体复合物的迁移率与自由、未络合分析物的迁移率不相等，则会发生手性分离。当络合常数、络合迁移率或这两个参数中的差异存在时，立体异构体就可以分离。在等速电泳分离中，形成一个迁移的稳态，其中分析物要么建立具有平台浓度的连续区，要么如果存在量不足，则以峰状分布的形式在移动的稳态边界内迁移。模拟数据首次说明了使用间隔化合物的用途，该化合物在对映体之间建立等速电泳区，从而实现对映体的完全分离，并有可能在峰模式等速电泳中进行单独检测。它们证明，这种方法可用于评估手性化合物的对映体纯度。
