A stereoselective method, involving a single liquid-liquid extraction
step, was developed and validated for the analysis of nadolol in human
plasma, The assay involved extraction of nadolol and desmethyl-nadolo
l (as internal standard (IS)) from alkalinized plasma into dichloromet
hane, The organic solvent was separated and evaporated under nitrogen
at 40 degrees C, A chiral derivatization scheme with (R-(-)-napthyleth
ylisocyanate (50 mu L of 0.1% solution in dichloromethane for 60 min)
was employed to convert the enantiomers of nadolol into the correspond
ing diastereomeric derivatives, The residue was reconstituted in the m
obile phase and injected onto a C-18 column, The mobile phase was a mi
xture of methanol:tetrahydrofuran:water 152:7:41 by vol) containing ab
out 0.001% v/v of both phosphoric acid and tetramethylethylenediamine.
Fluorimetric detection was performed at excitation 230 and emission 3
30 nm, The assay was specific for the enantiomers of nadolol and the l
ower limit of quantitation was 2 ng/mL for each of the enantiomers, An
alysis of quality control samples resulted in precision estimates of 7
% RSD for inter-assay and 10.1% RSD for intra-assay and the predicted
concentrations deviated less than 9.4% of the nominal values for the f
our enantiomers, The extraction recoveries of the individual enantiome
r was about 70%, Stability of nadolol enantiomers were established for
four freeze/thaw cycle periods and in the autosampler at 5 degrees C
for at least 116 h.