RAPID ASSAY FOR THE DETERMINATION OF TOLFENAMIC ACID IN PHARMACEUTICAL PREPARATIONS AND BIOLOGICAL-FLUIDS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

An improved reversed-phase High-Performance Liquid Chromatographic (HPLC) method using UV detection, at 282 nm, is described for the determination of tolfenamic acid in the presence of caffeine, as internal standard, in pharmaceutical preparations and biological fluids. Sample analyses are performed with a Lichrosorb-RP18, 10-mu-m, 250x4 mmI.D., column using acetate buffer, (pH 4.6 and constant ionic strength 0.05 M) methanol (18:82) as eluent, at a flow rate of 1.9 ml/min. The retention time is 1.44 min for caffeine and 2.62 min for tolfenamic acid. The absolute detection limit is 0.5 ng in the presence and 0.9 ng in the absence of internal standard and linearity is observed up to 100 ng injected. The method involves the use of solid-phase extraction for sample clean-up and subsequent separation of tolfenamic acid and internal standard from endogenous interfering compounds on a reversed-phase column. The method outlined in this paper is applied to the determination of tolfenamic acid in pharmaceutical formulations (capsules, suspension) and biological fluids (blood serum and urine). The method can be readily utilised for clinical pharmacokinetic studies.