Improved determination of tramadol hydrochloride in biological fluids and pharmaceutical preparations utilizing a modified carbon paste electrode

A simple, rapid and sensitive method for the determination of tramadol hydrochloride in urine, milk and pharmaceutical preparations using two modified carbon paste electrodes was developed. One electrode (sensor A) is based on ion-association of tramadol hydrochloride with phosphotungstic acid (TD-PT) and the other (sensor B) with a mixture of phosphotungstic acid (TD-PT) and silicomolybdic acid (TD-SM). Among seven different solvent mediators tested, 2-nitrophenyl octyl ether (NPOE) exhibited a proper behavior including Nernstian slopes of the calibration curve at 57.8 ± 0.4 and 56.5 ± 0.8 mV per decade for sensors A and B. The response times were 8 and 5 s; detection limits 6.2 × 10−6 and 1.8 × 10−6 M; the concentration range 9.2 × 10−6 to 1.0 × 10−1 M and 5.5 × 10−6 to 1.0 × 10−1 M respectively. The present electrodes show good discrimination of tramadol hydrochloride from several inorganic, organic ions, sugars and some common drug excipients. The sensors were applied for the determination of tramadol hydrochloride in urine, milk and pharmaceutical preparations using potentiometric determination, standard addition and the calibration curve methods. The results obtained were satisfactory with excellent percentage recovery comparable and sometimes better than those obtained by other routine methods for the assay.