Three quality control (QC) standard solutions, with three different
concentrations (3.5, 15 and 28 ng mL1 for enantiomers of the
NFLX and 6.0, 30 and 56 ng mL1 for enantiomers of the FLX), each
one in triplicate, were prepared to assess the accuracy and intraand
inter-batch precision. The accuracy of the method was evaluated
as the percentage of agreement between the concentrations
of the standards analysed in the SPE extracts and the nominal concentration
(Validation of Analytical Procedures: Text and Methodology
Q2(R1), 1996; Bioanalytical method validation: Guidance for
Industry, 2001; Madureira et al., 2009; 2010). Precision was expressed
by the relative standard deviation (RSD) of the replicate
measurements. Fortified matrices at the same QC concentrations
were used for the recovery assays and the evaluation of efficiency
of the extraction. It was calculated by comparing the peak areas of
the standards from the spiked matrix with those of similar concentrations
in ethanolic standard solutions.