Determination of ibuprofen and naproxen in tablets

Ibuprofen and naproxen have been quantified in tablets by capillary isotachophoresis. Hydrochloric acid (10 mmol/l) adjusted with creatinine to pH 5.0 plus 0.1% polyvinylpyrrolidone was used as the leading electrolyte and 10 mmol/l 4-morpholineethanesulfonic acid as the terminating electrolyte. Linearity was observed from 40.0 to 200.0 mg/l of ibuprofen (naproxen), with a coefficient of determination (r²) of 0.999. Good quantitation was obtained in short analysis time. The isotachophoretic results were compared with those obtained by the fluorescence spectrometry. Experimental parameters for ibuprofen were: λ_EX=224 nm and λ_EM=290 nm. Experimental parameters for naproxen were: λ_EX=230 nm and λ_EM=355 nm. The calibration plot was found to be linear in the range 0.4–2.4 mg/l for ibuprofen and 5.0–20.0 μg/l for naproxen. The minimal sample pretreatment and relatively low running cost make isotachophoresis a good alternative to existing methods.