An improved HPLC method overcoming Beer's law deviations arising from supramolecular interactions in tolfenamic acid and cyclodextrins complexes

Inclusion complexes of tolfenamic acid (TA), a non-steroidal anti-inflammat ory drug, with methyl-beta cyclodextrin and hydroxypropyl-beta cyclodextrin were prepared and characterised. Spectrophotometric, chromatographic (RP-H PLC) and H-1 NMR studies of the complexes were conducted. It was observed t hat cyclodextrins influence TA's molar absorptivity leading to Beer's law d eviation. Consequently, the accuracy problem arose, urged for the applicati on of specific chromatographic conditions for the determination of TA in th e presence of CDs. A new HPLC method was developed and validated. TA was an alysed on a C18 column 5 mu m (150 x 4.6 mm), using a column thermostat reg ulated at 30 degrees C. The mobile phase consisted of methanol-phosphate bu ffer solution (pH 3.2; 0.07 M) (90:10 v/v) and the flow rate was set at 2.0 mi min(-1). The detector was operated at 286 nm. TA was successfully deter mined, overcoming the problems arising from the presence of cyclodextrins. (C) 1998 Elsevier Science B.V. All rights reserved.