STUDIES ON THE STABILITY OF N-ALKYL-BONDED SILICA-GELS UNDER BASIC PH CONDITIONS

Mobile phase and stationary phase parameters that influence stability of silica-based reversed phases are examined under high pH conditions. Mobile phases containing 0.1 M NaOH and variable methanol content were cycled through columns packed with various alkyl-bonded phases. Chromatography of small molecules and %C analysis were used to probe changing chromatographic performance as phase hydrolysis proceeded. It was evident that the rate of bonded phase hydrolysis was increased when the 0.1 M NaOH solution contained a high amount of organic solvent, especially when followed by a high organic-containing acidic wash. C4 bonded phases were less stable than C18 bonded phases. In the latter case, low bonded ligand coverage or the lack of endcapping also reduced stability against base hydrolysis. Reversed phases bonded to acid-washed silica showed greater base stability than those bonded to non-treated silica. The use of a silica precolumn did not serve to increase system usefulness. However, the use of soluble sodium silicate in the NaOH solution increased column lifetime for both short (i.e. C4) and long (i.e. C18) n-alkyl chain reversed phases. © 1990.