Problems connected with HPLC separation of pilocarpine from its degradation products by means of silica gel and water-based mobile phase.

HPLC separation of pilocarpine from its degradation products (isopilocarpine, pilocarpic acid and isopilocarpic acid) was studied on unmodified silica gel stationary phase. An acidified aqueous solution of inorganic salts with addition of methanol served as the mobile phase. The influence of silica gel used, methanol content, mobile phase pH, anion of acids and/or inorganic salts and column temperature on solute retention, separation selectivity as well as peak shape was studied and partly explained. A significant dependence of the properties of the resulting separation system on the silica gel used was found. A test was proposed for evaluation of silica gel suitability.