Sensitive bromatometric methods for the assay of metaprolol tartrate in dosage forms

Abstract

One titrimetric and two spectrophotometric methods are described for the determination of metaprolol tartrate (MPT) using bromate-bromide mixture and two dyes, methyl orange and indigo carmine, as reagents. In titrimetry, an acidified solution of MPT is reacted with a known excess of bromate-bromide mixture and after a pre-determined time, the unreacted bromine is determined by iodometric titration. The spectrophotometric methods involve the addition of a known excess of bromate-bromide mixture to MPT in acidic medium followed by determination of the residual bromine by reacting with fixed amount of either methyl orange and measuring the absorbance at 520 nm (Method A) or indigo carmine and measuring the absorbance at 610 nm (Method B). In all the methods, amount of bromine reacted corresponds to the amount of MPT. The working conditions of the methods have been optimised. Titrimetry allows the determination of MPT in 2.5 - 7.5 mg range and the calculations are based on a 1:1(MPT : KBrO₃) reaction stoichiometry. In the spectrophotometric methods, Beer’s law is valid over the concentration ranges 0.5 -5.0 and 1.5 - 15.0 <img src='/image/spc_char/micro.gif' border=0>g mL^-1 MPT for method A and method B, respectively. Method A with a molar absorptivity of 8.17 <img src='/image/spc_char/cross.gif' border=0> 10⁴ L mol^-1cm^-1is more sensitive than method B (€ = 2.70 <img src='/image/spc_char/cross.gif' border=0> 10⁴ L mol^-1cm^-1). The limits of detection and quantification are reported for both the methods. The methods could usefully be applied to routine quality control of tablets containing MPT. No interference was observed from common pharmaceutical adjuvants. Statistical comparison of the results with those obtained by an established UV-spectrophotometric method showed excellent agreement and indicated no significant difference in accuracy and precision. The reliability of the methods was further ascertained by recovery studies.