Trammell B C, Hillmyer M A, Carr P W
Department of Chemistry, University of Minnesota, Minneapolis 55455, USA.
Anal Chem. 2001 Jul 15;73(14):3323-31. doi: 10.1021/ac010032k.
Polybutadiene-coated zirconia (PBD-ZrO2) is very useful for reversed-phase separations under a wide variety of conditions. Its excellent chemical (pH = 1-13) and thermal (up to 150 degrees C) stability distinguish it from silica-based reversed phases. Just as with silica-based phases, zirconia's surface chemistry significantly influences the chromatography of certain classes of analytes. Zirconia's hard Lewis acid sites can be chromatographically problematic. Analytes such as carboxylic acids strongly interact with these sites on PBD-ZrO2 and do not elute. Addition of phosphate or other strong, hard Lewis bases to the eluent brings about elution, but the resulting peak is often tailed and broad. Typically, cationic solutes are more retained in the presence of phosphate or fluoride due to adsorption of the Lewis base additives and the concomitant development of a negative charge on the surface. This Coulombic interaction can be used to optimize selectivity, but the reversed-phase-cation-exchange retention can produce broad peaks with excessive retention. As an alternative to adding Lewis bases to the eluent, we studied the effect of permanently modifying PBD-ZrO2 by covalently attaching vinylphosphonic acid (VPA) to PBD which was predeposited in the pores of zirconia. We have investigated the chromatography of acids, bases, and small peptides on VPA-modified PBD-ZrO2 (VPA-PBD-ZrO2) and compared it to PBD-ZrO2. VPA-PBD-ZrO2 is a reversed-cation-exchange phase with properties quite different from PBD-ZrO2. The chemical stability of both phases led us to explore how low-pH (1.5-3), ultralow-pH (0), and high-pH (12) eluents effect the retention properties of these mixed-mode phases. Ultralow-pH eluents effectively separate small peptides on both phases. This approach gives lower retention, without sacrificing resolution, and much higher efficiency for small peptides than previously reported.
聚丁二烯包覆的氧化锆（PBD-ZrO₂）在多种条件下对反相分离非常有用。其出色的化学稳定性（pH = 1 - 13）和热稳定性（高达150摄氏度）使其有别于基于硅胶的反相填料。与基于硅胶的填料一样，氧化锆的表面化学性质对某些类别的分析物的色谱行为有显著影响。氧化锆的硬路易斯酸位点在色谱方面可能存在问题。羧酸等分析物会与PBD-ZrO₂上的这些位点强烈相互作用，从而无法洗脱。向洗脱液中添加磷酸盐或其他强的、硬的路易斯碱可实现洗脱，但得到的峰通常会拖尾且变宽。通常，由于路易斯碱添加剂的吸附以及表面随之产生的负电荷，阳离子溶质在存在磷酸盐或氟化物的情况下保留更强。这种库仑相互作用可用于优化选择性，但反相 - 阳离子交换保留可能会产生峰宽且保留过度的情况。作为向洗脱液中添加路易斯碱的替代方法，我们研究了通过将乙烯基膦酸（VPA）共价连接到预先沉积在氧化锆孔中的PBD上，对PBD-ZrO₂进行永久改性的效果。我们研究了酸、碱和小肽在VPA改性的PBD-ZrO₂（VPA-PBD-ZrO₂）上的色谱行为，并将其与PBD-ZrO₂进行了比较。VPA-PBD-ZrO₂是一种反相阳离子交换填料，其性质与PBD-ZrO₂有很大不同。两种填料的化学稳定性促使我们探索低pH（1.5 - 3）、超低pH（0）和高pH（12）洗脱液如何影响这些混合模式填料的保留特性。超低pH洗脱液能有效分离两种填料上的小肽。这种方法能降低保留，同时不牺牲分离度，并且对于小肽而言，效率比之前报道的要高得多。
