Davies Nicola H, Euerby Melvin R, McCalley David V
Centre for Research in Biomedicine, University of the West of England, Frenchay, Bristol BS16 1QY, UK.
J Chromatogr A. 2008 Jan 18;1178(1-2):71-8. doi: 10.1016/j.chroma.2007.11.040. Epub 2007 Nov 19.
The retention and mass overload of five bases and a quaternary ammonium compound were studied on a bridged ethyl hybrid inorganic/organic phase (XBridge C18) over a pH range 2.7-12.0 using acetonitrile-phosphate and carbonate buffers. Some comparisons were drawn with results on a methyl hybrid (XTerra) phase. At low pH, rapid mass overload was observed with severe decreases in efficiency as sample mass was increased over the range 0.04-5 microg of solute. At intermediate pH (swpH 7.0), generally good peak shapes for small sample mass were still obtained on the ethyl hybrid, but with somewhat increased tailing of bases compared with swpH 2.7. At higher pH (swpH 10), good peak shape and improved loadability were obtained for moderately strong bases, due to their occurrence mostly as neutral species. However, stronger bases gave poor efficiency, attributed to interaction of the charged basic solute with increasingly ionised column silanol groups. Results were broadly similar on the methyl hybrid at swpH 10. At swpH 11, unusual profiles of increasing followed by decreasing efficiency were obtained on the ethyl hybrid for some bases as sample mass was increased; improved results were obtained at swpH 12. While the column loadability increased substantially at the highest pH studied, tailing for small sample mass was still more severe than at low pH, even though all compounds were <1% ionised in the mobile phase.
在pH值2.7 - 12.0范围内，使用乙腈 - 磷酸盐和碳酸盐缓冲液，研究了五种碱基和一种季铵化合物在桥连乙基杂化无机/有机相（XBridge C18）上的保留和质量过载情况。与甲基杂化（XTerra）相的结果进行了一些比较。在低pH值下，当溶质质量在0.04 - 5微克范围内增加时，观察到快速的质量过载，且效率严重下降。在中间pH值（pH 7.0）时，乙基杂化相上对于小质量样品通常仍能获得良好的峰形，但与pH 2.7相比，碱基的拖尾有所增加。在较高pH值（pH 10）时，由于中等强度碱基大多以中性物种存在，因此能获得良好的峰形和提高的负载能力。然而，更强的碱基效率较差，这归因于带电碱性溶质与越来越多电离的柱硅醇基团的相互作用。在pH 10时，甲基杂化相上的结果大致相似。在pH 11时，随着样品质量增加，乙基杂化相上一些碱基出现了先增加后降低的异常效率曲线；在pH 12时获得了更好的结果。虽然在所研究的最高pH值下柱负载能力大幅增加，但即使所有化合物在流动相中电离度均小于1%，小质量样品的拖尾仍比低pH值时更严重。
