Innovative design of a methodology for the simultaneous determination of compounds by kinetic-spectroscopy three-dimensional chemiluminescence.

This report presents a novel methodology based in the quickly acquisition of full UV-vis range spectra combined with the joint determination of kinetic parameters and chemiluminescence signals. Then this technique allows obtaining three-dimensional chemiluminescence spectra profiles containing kinetic and spectroscopic information. That is especially useful for resolving mixtures of luminophors because of more analytical information for each analyte is available increasing the selectivity relative to conventional chemiluminescence methods. To accomplish this, a conventional Back-Thinned CCD detector is used and the three-dimensional chemiluminescence spectra is subsequently processed so that two-dimensional spectra with different trajectories can be obtained by dedicated software CLTotal. The potential of the proposed analytical methodology was assessed for the simultaneous determination of two polycyclic aromatic hydrocarbons. The chemiluminescent reaction between DNPO and hydrogen peroxide induced by their presence was used to record 3D spectra and the software CLTotal to subsequently construct linear variable-angle trajectories in the spectra, in order to obtain more selective 2D spectra facilitating the simultaneous determination of the analytes. The results of the statistical analysis testify to the usefulness of the proposed method for the intended purpose.

Simultaneous determination of doxycycline and chlortetracycline in real samples by europium-sensitized luminescence.

A simple luminescent methodology for the simultaneous determination of doxycycline and chlortetracycline in pharmaceutical preparations and human urine is proposed. Since the native fluorescence of both analytes is negligible, this method takes advantage of the lanthanide-sensitized luminescence, which provides increased sensitivity. Due to the strong overlapping between the luminescence spectra of both europium complexes, the use of luminescence decay curves to resolve mixtures of the analytes is proposed, particularly as these curves are more selective. A factorial design, with three levels per factor, coupled to a central composite design was selected to obtain a calibration matrix of 13 standards plus one blank sample, which were processed with a partial least-squares analysis. In order to assess the effectiveness of the proposed method, a prediction set of 10 synthetic samples was analyzed, and recovery percentages between 95 and 104% were obtained. Limits of detection, calculated by means of a new criterion, were 3.27 and 1.06 µg L(-1) for doxycycline and chlortetracycline, respectively. The method was tested in three different pharmaceutical preparations containing the analytes, with average recovery percentages of 99.4 ± 1.8 for doxycycline and 100.5 ± 2.1 for chlortetracycline. Moreover, a central composite design was also developed to obtain a calibration matrix that made feasible the simultaneous determination of both tetracyclines in human urine samples. In this case, average recovery percentages were 98.0 ± 4.4 and 97.8 ± 4.6 for doxycycline and chlortetracycline, respectively. No extraction method or prior separation of the analytes was needed.

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.