MethodValidation. Specificity was determined by analy-sis of blank urine, without addition of morphine and codeine
to determine possible interference with these compounds.
To evaluate the linearity, the calibration curves were
generated using the analyte peak area by linear regression
on three consecutive days. The LLOQ was estimated in the
process of calibration curve construction and was defined
as the lowest concentration for which precision (RSD) was
better than 20%.
QC samples at three concentration levels (50, 200, and
1600ng/mL for morphine and codeine) were analyzed to
assess the accuracy and precision of the method. Again, the
assays were performed on three separate days, and on each
day six replicates of the QC samples at each concentration
level were analyzed. The assay accuracy was calculated as
relative error. The assay precision for each QC level was
determined as the relative standard deviation (RSD) of the
measured concentrations. The intra- and interday precisions
were required to be below 15%, and the accuracywas required
to be within±15%.