Abstract
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 <i>µ</i>g
L<sup>-1</sup> 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.
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