HPLC analysis of thimerosal in ophthalmic solution. Comparing electrochemical with spectrophotometric detectors.

Electrochemical and spectrophotometric detectors for the reversed phase HPLC analysis of thimerosal in an ophthalmic formulation were evaluated with respect to response linearity, recovery, and lower limit of detection. The electrochemical oxidation of thimerosal at a glassy carbon electrode was characterized by both cyclic voltammetry and thin layer amperometry. The hydrodynamic half-wave potential for thimerosal (+0.6 V) was determined using a coulometric detector. The relatively low oxidation potential for thimerosal forms the basis for this highly sensitive and selective analytical technique. The amperometric lower limit of detection for thimerosal (at signal/noise = 2) was less than 400 pg. The detection limit with spectrophotometric detection at 254 nm was approximately 20 ng, a 50 fold increase.