Analysis of chlorhexidine sorption in soft contact lenses by catalytic oxidation of [14C]chlorhexidine and by liquid chromatography.

Two methods are described for the analysis of chlorhexidine sorption in soft contact lenses. The first is an isocratic ion-pairing high-performance liquid chromatographic (HPLC) method with UV detection at 220 nm that allows the determination of chlorhexidine, p-chloroaniline, and other chlorhexidine degradation products in ophthalmic solutions. This procedure had a detection limit of 0.1 ng. The second involves the catalytic oxidation of the lens matrix containing [14C]chlorhexidine to [14C]carbon dioxide and water. The label is then trapped as carbon dioxide in a cocktail and is analyzed by liquid scintillation counting. These methods are sensitive, accurate, and reproducible, and can be used independently or in conjunction for the determination of chlorhexidine sorption in soft contact lenses.