Spectrophotometric determination of labetalol in pharmaceutical preparations and spiked human urine.

Two simple and sensitive spectrophotometric methods were developed for the spectrophotometric determination of labetaolol (LBT). Both methods are based on the phenolic nature of the drug. The first method (Method I) is based on coupling LBT with diazotized benzocaine in presence of trimethylamine. A yellow colour peaking at 410 nm was produced and its absorbance is linear with the concentration over the range 1-10 microg ml(-1) with correlation coefficient (n=5) of 0.9993. The molar absorptivity was 2.633 x 10(4) l mol(-1) cm(-1). The second method (Method II) involves coupling LBT with diazotized p-nitroaniline in presence of sodium carbonate. An orange colour peaking at 456 nm was obtained and its absorbance is linear with concentration over the range 1-10 microg ml(-1) with correlation coefficient (n=5) of 0.99935. The stoichiometry of the reaction in both cases was accomplished adopting the limiting logarithmic method and was found to be 1:1. The developed method could be successfully applied to commercial tablets. The results obtained were in good agreement with those obtained using the official methods. No interference was encountered from co-formulated drugs, such as hydrochlorothiazide. The method was further extended to the in-vitro determination of LBT in spiked human urine. The % recovery (n=4) were 97.7+/-5.75 and 103.27+/-5.42 using the Methods I and II, respectively.

Spectrofluorometric determination of labetolol in pharmaceutical preparations and spiked human urine through the formation of coumarin derivative.

A simple, sensitive and specific spectrofluorimetric method has been developed for the determination of labetalol (LBT). The method is based on the reaction between LBT and ethylacetoacetate in the presence of sulphuric acid to give yellow fluorescent product with excitation wavelength of 312 nm and emission wavelength of 432 nm. The reaction conditions were studied and optimized. The fluorescence intensity-concentration plot is rectilinear over the range 1-15 microgram/ml with minimum detectability limit of 0.8 microgram/ml (2.16 x 10(-6) M). The proposed method was successfully applied to commercial tablets containing LBT, the percentage recoveries agreed well with those obtained using the official methods. Hydrochlorothiazide, which is frequently co-formulated with LBT did not interfere with the assay. The method was further extended to the in-vitro determination of LBT in spiked human urine samples. The percentage recovery was 101.50+/-6.18 (n=6). A proposal of the reaction pathway was postulated.