A simple and highly sensitive spectrofluorimetric method has been developed for the determination of labetalol (LBT) in pharmaceutical preparations and biological fluids. The method is based on the reaction between the nitroso-derivative of LBT and 2-cyanoacetamide (2-CAA) in the presence of ammonia to give fluorescent product with excitation wavelength of 335 nm and emission wavelength of 420 nm. The reaction conditions were studied and optimized. The fluorescence intensity-concentration plot is rectilinear over the concentration range of 0.025-0.250 μg/mL with minimum detectability of 1.40 ng/mL (3.6×10-9 M). The proposed method was successfully applied to commercial tablets containing LBT; the percentage recoveries agreed well with those obtained using the reference method. The method was further extended to the in-vitro determination of LBT in spiked human urine and plasma samples. The percentage recovery was 100.10 ± 3.44 and 101.27 ± 4.97, respectively. A proposed reaction pathway was postulated.
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