Serum samples (10L) were spiked with a known amount
(10L) of each standard at four different concentrations and were
treated in a manner similar to that described above. A calibration
curve was constructed by plotting the peak area ratio to the IS of
each spiked sample against the added concentration, and aworking
curve was constructed by plotting the peak area of the IS against
the concentration. Precision was expressed as the relative standard
deviation (RSD, %), and the accuracy was expressed as the relative
mean error (RME, %). The equations used to calculate RSD and RME
were as follows: RSD (%) = (standard deviation/mean)×100 and