Chemical stability of reversed phase high performance liquid chromatography silica under sodium hydroxide regeneration conditions

Chromatographic sorbents used within the purification of peptide or protein based active pharmaceutical ingredients (APIs) are commonly subjected to caustic regeneration procedures, so-called CIP treatments. While polymeric materials remain unaffected by this treatment, silica-based sorbents are at an intrinsic risk of dissolution under high pH conditions, such as, e.g. 0.1M NaOH. It is common misconception that silica-based materials simply cannot be subjected to alkaline conditions above pH 9. Moreover, most studies covering the chemical stability of HPLC sorbents above pH 9 have been limited to the chromatographic conditions used for the separations themselves. Such studies have used buffered mobile phases up to pH 11 or 12. Very little focus has been put on the stability of the stationary phases when subjected to shorter but harsher pH conditions required for regeneration purposes, such as 0.1M NaOH (pH 13). Knowledge about the amount of so-called leachables, degradation products originating from the stationary phase, is of growing importance for the registration of pharmaceuticals for human use and is addressed in this work. This study compares the chemical stability of different commercially available reversed phase silica materials (C18) that are used in industrial scale preparative HPLC. The silica materials were subjected to NaOH regeneration conditions and it is shown that some materials are able to withstand 0.1M NaOH conditions without significant harm. It is demonstrated that contaminants present in the effluent in the range of 10-50 microg/mL can lead to significant contamination of API product fraction.