Influence of cations and anions of ionic liquids and salts as additives in RP HPLC systems to the analysis of alkaloids on C18 and Polar RP columns

The ionic nature of basic compounds gives rise to broad asymmetrical chromatographic peaks in RP systems containing a mixture of organic modifiers and water as mobile phases. The addition to the mobile phase of a reagent to block the silanol sites such as salts containing chaotropic anions or ILs gives significantly more symmetric peaks and a high resolution of basic analytes. In systems containing the addition of salts or ILs, the retention of ionic analytes is a consequence of the combination of a mixed mechanism that involves chaotropic, ion-exchange, hydrophobic, and ion-pairing interactions. In this work, the influence of salts consisting of various anions and ILs consisting of various cations and anions on the retention and peak symmetry of alkaloids in RP HPLC systems on C18 and Polar RP columns was investigated. The multiple interactions that salts and ILs experience inside the chromatographic system suggest that the alkaloid-suppressing potency should be measured based on the shape of the chromatographic peaks. In order to better understand the retention mechanism, the retention and symmetry of peaks obtained on both stationary phases and in systems containing salts and ILs were compared.碱性化合物的离子特性会在以有机改性剂与水的混合物作为流动相的反相色谱（RP）系统中产生宽幅不对称的色谱峰。向流动相中添加可封闭硅醇位点的试剂，例如含离液阴离子的盐类或离子液体（ILs），可显著获得对称性更佳的色谱峰，并实现碱性分析物的高分离度。在添加盐类或离子液体的色谱体系中，离子分析物的保留行为是多种混合机制共同作用的结果，这些机制包括离液作用、离子交换、疏水作用以及离子对相互作用。本研究考察了含不同阴离子的盐类，以及含不同阴、阳离子的离子液体，在以C18柱与极性反相（Polar RP）柱为固定相的反相高效液相色谱（RP HPLC）系统中，对生物碱保留行为与峰对称性的影响。盐类与离子液体在色谱系统内所产生的多重相互作用表明，抑制生物碱非特异性吸附的效能应基于色谱峰的峰形进行评估。为进一步阐明保留机制，本研究对比了两种固定相上以及添加盐类与离子液体的体系中所得色谱峰的保留行为与对称性。