Determination of Naproxen and its Metabolite, 6‐O‐Desmethylnaproxen, in Human Urine by Capillary Isotachophoresis

Abstract Analysis of naproxen (NP) and 6‐O‐desmethylnaproxen (DNP) in human urine samples was carried out using a column‐coupling isotachophoretic analyzer equipped with a conductivity detector. The preseparation capillary (80 mm×0.8 mm I.D.) was connected with an analytical capillary (160 mm×0.3 mm I.D.). The preseparation capillary was filled with the leading electrolyte (LE): 20 mM hydrochloric acid adjusted with creatinine to pH 5.0; 0.1% methylhydroxypropylcellulose. The analytical capillary was filled with the LE: 10 mM hydrochloric acid adjusted with β‐alanine to pH 4.0; 0.1% methylhydroxypropylcellulose. The terminating electrolyte was 10 mM 2‐(N‐morpholino)‐ethanesulfonic acid adjusted with tris(hydroxymethyl) aminomethane to pH 6.9. Limit of quantitation was 1.4 µg/mL for NP and 0.5 µg/mL for DNP. The proposed method was successfully applied to the direct determination of free NP and DNP in urine samples. The total of free and conjugated NP and DNP was obtained by including an alkaline hydrolysi...