Institute of Chemistry, University of Campinas, Campinas, SP, Brazil.
J Sep Sci. 2011 Nov;34(21):3011-9. doi: 10.1002/jssc.201100345. Epub 2011 Sep 21.
Complex analyses of polar compounds, especially basic ones, require more selective stationary phases. The present paper describes a stationary phase prepared by thermal immobilization of poly(methyltetradecylsiloxane) onto chromatographic silica (PMTDS-SiO(2)). This stationary phase presents hydrophobic and ion-exchange interactions that confer both high retention and unique selectivities for basic solutes. The influence of ion-exchange interactions is confirmed by the increase in retention factors of basic solutes when the mobile-phase pH changes from acidic to neutral and by the decrease in retention factors when the mobile-phase pH changes from neutral to alkaline. The ion-exchange properties of the stationary phase are enriched in neutral mobile phase (pH 7-7.5) using soft Lewis bases such as tricine and tris as buffers but are suppressed in both acidic (pH 2.5-6) and highly alkaline mobile phases (pH≤10). Increasing both temperature and flow rate permits more rapid separations while maintaining the selectivity. The stability of the stationary phase is evaluated with acid, neutral and alkaline mobile phases.
复杂的极性化合物分析，特别是碱性化合物，需要更具选择性的固定相。本文描述了一种通过将聚甲基十四烷基硅氧烷（PMTDS）热固定到色谱硅胶（PMTDS-SiO2）上制备的固定相。这种固定相具有疏水性和离子交换相互作用，赋予了碱性溶质高保留和独特的选择性。通过改变流动相 pH 值从酸性变为中性时碱性溶质的保留因子增加，以及从中性变为碱性时保留因子降低，证实了离子交换相互作用的影响。在中性流动相（pH7-7.5）中使用三羟甲基甘氨酸和三（羟甲基）氨基甲烷等软路易斯碱作为缓冲剂，可以增强固定相的离子交换特性，但在酸性（pH2.5-6）和高碱性流动相（pH≤10）中则会受到抑制。同时提高温度和流速可以在保持选择性的同时实现更快速的分离。使用酸性、中性和碱性流动相评估了固定相的稳定性。
