Kord A S, Khaledi M G
Department of Chemistry, North Carolina State University, Raleigh 27695-8204.
Anal Chem. 1992 Sep 1;64(17):1901-7. doi: 10.1021/ac00041a027.
The effects of concentrations of organic solvent and surfactant on elution strength and selectivity in MLC and IPC are studied. It is observed that selectivity between most pairs of solutes used in this study increases in MLC and either decreases or passes through a minimum in IPC, with the volume fraction of organic modifier. In both MLC and IPC, selectivity varies with surfactant concentration; however, the overall variation in selectivity and elution order are more pronounced in MLC. The solvent strength decreases in IPC and increases in MLC as a result of an increase in surfactant concentration. An iterative regression design is used to predict the optimum mobile-phase compositions in terms of solvent strength and selectivity. The correlation between the predicted and measured chromatograms is excellent in MLC and poor in IPC. This is due to a more regular and reproducible retention behavior in MLC which greatly facilitates the development of robust methodologies. For a mixture of amino acids and peptides, a large retention gap between the first and the last eluting solutes is observed in IPC, which makes the use of organic solvent gradient inevitable. However, a better separation for the same mixture of solutes can be achieved in MLC isocratically. Apparently, the general elution problem can be alleviated in MLC by using an optimum eluent composition. It is observed that the efficiencies of MLC and IPC are comparable. The above observations indicate that MLC can be a powerful alternative to IPC in order to achieve optimized separations in shorter analysis time.
研究了有机溶剂和表面活性剂浓度对多层涂层柱色谱（MLC）和离子对色谱（IPC）中洗脱强度和选择性的影响。观察到，在MLC中，本研究中使用的大多数溶质对之间的选择性随着有机改性剂的体积分数而增加，而在IPC中则降低或经过一个最小值。在MLC和IPC中，选择性均随表面活性剂浓度而变化；然而，MLC中选择性和洗脱顺序的总体变化更为明显。由于表面活性剂浓度的增加，IPC中的溶剂强度降低，而MLC中的溶剂强度增加。采用迭代回归设计来预测溶剂强度和选择性方面的最佳流动相组成。预测色谱图与实测色谱图之间的相关性在MLC中非常好，而在IPC中则很差。这是由于MLC中保留行为更规则且可重复，极大地促进了稳健方法的开发。对于氨基酸和肽的混合物，在IPC中观察到第一个和最后一个洗脱溶质之间存在较大的保留差距，这使得使用有机溶剂梯度不可避免。然而，在MLC中采用等度洗脱可以实现对相同溶质混合物更好的分离。显然，通过使用最佳洗脱液组成，MLC中的一般洗脱问题可以得到缓解。观察到MLC和IPC的效率相当。上述观察结果表明，为了在更短的分析时间内实现优化分离，MLC可以成为IPC的有力替代方法。
