Validation. The developed method was validated as
per the recommendations of USFDA Guidance for
Industry: Bioanalytical Method Validation [7]. Selec
tivity was studied at the Lower Limit of Quantification
(LLOQ) of 100 ng/mL by comparing the blank re
sponses of plasma from six different sources with the
peak areas afforded by the LLOQ samples. Accuracy
and precision were studied by analyzing five replicates
of the Lower Quality Control (LQC), Middle Quality
Control (MQC), and Higher Quality Control (HQC)
samples over five days. The concentration of guaifene
sin in the QC samples was determined by referring to
the area ratio of the drug to internal standard, obtained
from the QC samples, to the calibration equation gen
erated on the same day. The accuracy was estimated as
the mean % RE while the precision was measured in
the terms of % RSD.
The