Simultaneous determination of nabumetone and its principal metabolite in medicines and human urine by time-resolved fluorescence.

A simple fluorescent methodology for the simultaneous determination of nabumetone and its main metabolite, 6-methoxy-2-naphthylacetic acid (6-MNA), in pharmaceutical preparations and human urine is proposed. Due to the strong overlapping between the fluorescence spectra of both analytes, the use of fluorescence decay curves to resolve their mixture is proposed, since these curves are more selective. Values of dependent instrumental variables affecting the signal-to-noise ratio were fixed using a simplex optimization procedure. A factorial design with three levels per factor coupled to a central composite design was selected to obtain a calibration matrix of thirteen standards plus one blank sample that was processed using a partial least-squares (PLS) analysis. In order to assess the goodness of the proposed method, a prediction set of ten synthetic samples was analyzed, obtaining recovery percentages between 97 and 105%. Limits of detection, calculated by means of a new criterion, were 0.96 μg L(-1) and 0.88 μg L(-1) for nabumetone and 6-MNA, respectively. The method was also tested in the pharmaceutical preparation Relif, which contains nabumetone, obtaining recovery percentages close to 100%. Finally, the simultaneous determination of both analytes in human urine samples was successfully carried out by the PLS-analysis of a matrix of fifteen standards plus four analyte blanks and the use of the standard addition technique. Although urine shows native fluorescence, no extraction method or prior separation of the analytes was needed.