Ma Lianjia, Carr Peter W
Department of Chemistry, University of Minnesota, 207 Pleasant Sreet, SE, Minneapolis, Minnesota 55455, USA.
Anal Chem. 2007 Jun 15;79(12):4681-6. doi: 10.1021/ac0703303. Epub 2007 May 17.
Silica-based, reversed-phase liquid chromatographic (RPLC) stationary phases are very widely used to separate basic compounds in acidic eluents due to their high efficiency, good mechanical strength, and the versatile selectivity offered by different functional groups and the chemistry on the silica surface. However, the stability in acid of most silica-based stationary phases is poor, especially at elevated temperatures, due to hydrolysis of the siloxane bonds, which hold silanes on the silica substrate. This hydrolysis is commonly believed to be solely the result of catalysis by protons. However, we show that various metal cations (principally Fe3+/Fe2+, Ni2+, and Cr3+) released from acid corrosion of the stainless steel inlet frit greatly accelerate the hydrolysis of the siloxane bond. Furthermore, these metal cations, and not the high acidity per se, are mainly responsible for column instability. We show that removing the stainless steel inlet frit, or use of a titanium frit, greatly reduces or totally eliminates corrosion of the inlet frit and radically improves retention stability. The effects of various acids and types of organic modifier were also studied. These observations suggest a number of practical approaches that can significantly extend the lifetime of any RPLC stationary phase in acidic media at elevated temperature.
基于硅胶的反相液相色谱（RPLC）固定相由于其高效性、良好的机械强度以及硅胶表面不同官能团和化学性质所提供的多功能选择性，被广泛用于在酸性洗脱液中分离碱性化合物。然而，由于连接硅烷与硅胶基质的硅氧烷键发生水解，大多数基于硅胶的固定相在酸性条件下的稳定性较差，尤其是在高温下。通常认为这种水解仅仅是质子催化的结果。然而，我们发现不锈钢进样口滤片酸腐蚀释放出的各种金属阳离子（主要是Fe3+/Fe2+、Ni2+和Cr3+）极大地加速了硅氧烷键的水解。此外，主要是这些金属阳离子而非高酸度本身导致了色谱柱的不稳定性。我们表明，去除不锈钢进样口滤片或使用钛滤片可大大减少或完全消除进样口滤片的腐蚀，并从根本上提高保留稳定性。我们还研究了各种酸和有机改性剂类型的影响。这些观察结果表明了一些实用方法，可显著延长任何RPLC固定相在高温酸性介质中的使用寿命。
