Capillary isotachophoretic determination of flufenamic, mefenamic, niflumic and tolfenamic acid in pharmaceuticals

• Published in: Journal of pharmaceutical and biomedical analysis Vol. 23; no. 1; pp. 135 - 142
• Main Authors: POLASEK, M, POSPISILOVA, M, URBANEK, M
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.08.2000; Elsevier Science
• Subjects: Analysis; Anti-Inflammatory Agents, Non-Steroidal - analysis; Biological and medical sciences; Calibration; Dosage Forms; Electrophoresis - methods; Flufenamic acid; Flufenamic Acid - analysis; General pharmacology; Isotachophoresis; Medical sciences; Mefenamic acid; Mefenamic Acid - analysis; Niflumic acid; Niflumic Acid - analysis; ortho-Aminobenzoates - analysis; Pharmaceutical analysis; Pharmaceutical Preparations - chemistry; Pharmacology. Drug treatments; Reproducibility of Results; Tolfenamic acid; Flufenamic acid; Niflumic acid; Isotachophoresis; Pharmaceutical analysis; Tolfenamic acid; Mefenamic acid; Capillary column; Cream; Ointment; Colloidal gel; Analysis method; Dosage form; Hard capsule; Quantitative analysis
• ISSN: 0731-7085; 1873-264X
• DOI: 10.1016/S0731-7085(00)00283-1

Anionic capillary isotachophoresis (ITP) with conductimetric detection has been used for determining selected non-steroid anti-inflammatory and analgesic drugs of the phenamate group, namely tolfenamic ( I), flufenamic ( II), mefenamic ( III) and niflumic ( IV) acid. Initially the p K a values (proton lost) of I– IV were determined as 5.11, 4.91, 5.39 and 4.31, respectively, by the UV spectrophotometry in aqueous 50% (w/w) methanol. The optimised ITP electrolyte system consisted of 10 mM HCl+20 mM imidazole (pH 7.1) as the leading electrolyte and 10 mM 5,5′-diethylbarbituric acid (pH 7.5) as the terminating electrolyte. The driving and detection currents were 100 μA (for 450 s) and 30 μA, respectively (a single analysis took about 20 min). Under such conditions the effective mobilities of I– IV varied between 23.6 and 24.6 m 2 V −1 s −1 (evaluated with orotic acid as the mobility standard). The calibration graphs relating the ITP zone length to the concentration of the analytes were rectilinear ( r=0.9987–0.9999) in the range 10–100 mg l −1 of the drug standard. The R.S.D.s were 0.96–1.55% ( n=6) when determining 50 mg l −1 of the analytes in pure test solutions. The method has been applied to the assay of the phenamates in six commercial mass-produced pharmaceutical preparations (Mobilisin gel and ointment, Lysalgo capsules, Nifluril cream, Niflugel gel, and Clotam capsules). According to the validation procedure based on the standard addition technique the recoveries were 98.4–104.3% of the drug and the R.S.D. values were 1.25–3.32% ( n=6).