Pfizer Analytical Research Centre, Australian Centre for Research on Separation Science, School of Chemistry, University of Tasmania, Private Bag 75, Hobart, Tasmania 7001, Australia.
J Chromatogr A. 2010 Sep 24;1217(39):6069-76. doi: 10.1016/j.chroma.2010.07.040. Epub 2010 Aug 5.
The mixed-mode separation of a selection of anionic and cationic pharmaceutically related compounds is studied using ion-exchange columns and eluents consisting of ionic salts (potassium hydroxide or methanesulfonic acid) and an organic modifier (methanol). All separations were performed using commercially available ion-exchange columns and an ion chromatography instrument modified to allow introduction of methanol into the eluent without introducing compatibility problems with the eluent generation system. Isocratic retention prediction was undertaken over the two-dimensional space defined by the concentration of the competing ion and the percentage of organic modifier in the eluent. Various empirical models describing the observed relationships between analyte retention and both the competing ion concentration and the percentage of methanol were evaluated, with the resultant model being capable of describing the separation, including peak width, over the entire experimental space based on six initial experiments. Average errors in retention time and peak width were less than 6% and 27%, respectively, for runs taken from both inside and outside of the experimental space. Separations performed under methanol gradient conditions (while holding the competing ion concentration constant) were also modelled. The observed effect on retention of varying the methanol composition differed between analytes with several analytes exhibiting increased retention with increased percentage methanol in the eluent. An empirical model was derived based on integration of the observed t(R) vs. %methanol plot for each analyte. A combination of the isocratic and gradient models allowed for the prediction of retention time using multi-step methanol gradient profiles with average errors in predicted retention times being less than 4% over 30 different 2- and 3-step gradient profiles for anions and less than 6% over 14 different 2- and 3-step gradient profiles for cations. A modified peak compression model was used to estimate peak widths under these conditions. This provided adequate width prediction with the average error between observed and predicted peak widths being less than 15% for 40 1-, 2- and 3-step gradients for anions and less than 13% over 14 1-, 2- and 3-step gradients for cations.
采用离子交换柱和由离子盐（氢氧化钾或甲磺酸）和有机溶剂（甲醇）组成的洗脱液研究了选择的阴离子和阳离子药物相关化合物的混合模式分离。所有分离均使用市售的离子交换柱和经改装的离子色谱仪进行，该仪器可在不引入与洗脱液生成系统不兼容问题的情况下将甲醇引入洗脱液中。在洗脱液中竞争离子浓度和有机溶剂百分比所定义的二维空间中进行等度保留预测。评估了各种描述分析物保留与竞争离子浓度和甲醇百分比之间观察到的关系的经验模型，所得到的模型能够描述分离，包括基于六个初始实验的整个实验空间的峰宽。在实验空间内外进行的运行中，保留时间和峰宽的平均误差分别小于 6%和 27%。在甲醇梯度条件下进行的分离（保持竞争离子浓度恒定）也进行了建模。在不同分析物中观察到的甲醇组成对保留的影响不同，一些分析物随着洗脱液中甲醇百分比的增加而保留增加。根据每个分析物的观察到的 t(R)与 %甲醇图，推导出了一个经验模型。等度和梯度模型的组合允许使用多步甲醇梯度曲线预测保留时间，对于阴离子的 30 种不同的 2-和 3-步梯度曲线和阳离子的 14 种不同的 2-和 3-步梯度曲线，预测保留时间的平均误差小于 4%。使用改进的峰压缩模型来估计这些条件下的峰宽。对于阴离子的 40 种 1-、2-和 3-步梯度和阳离子的 14 种 1-、2-和 3-步梯度，观察到的和预测到的峰宽之间的平均误差小于 15%，这提供了足够的峰宽预测。
