Spectrophotometric determination of trimethoprim in pure form and in pharmaceutical preparations using bromothymol blue, bromocresol green and alizarin red S
A. El-ansary et al., Spectrophotometric determination of trimethoprim in pure form and in pharmaceutical preparations using bromothymol blue, bromocresol green and alizarin red S, ANAL LETTER, 32(5), 1999, pp. 955-969
Simple, sensitive and selective methods for the determination of trimethopr
im (TMP) in pure form and in pharmaceutical formulations are described. The
methods are based on the reaction of TMP as a pi-electron donor with bromo
thymol blue (BTB), bromocresol green (BCG) and alizarin red S (ARS) as elec
tron accepters. The coloured products are quantified spectrophotometically
at their corresponding lambda(max). Beer's law is obeyed in case of BTB in
the range 2.9-23.2 mu g/ml (CHCl3), 2.9-20.0 mu g/ml(CH2Cl2) and 5.0-29.0 m
u g/ml (ClC6H5), in the case of BCG 2.927.5)mu g/ml (H2O/alc.)2.9-18.3 mu g
/ml (CHCl3) and 2.9-20.3 mu g/ml(CH2Cl2) and for ARS in the range 3.0-12.0
mu g/ml in H2O/alc medium. The specific absorptivities, molar absorptivitie
s, Sandell sensitivities, standard deviations and percent recoveries are ev
aluated. Application of the suggested methods to dosage forms is presented
and compared with the pharmacopoeial method. The interference from additive
s and sulfa compounds, especially sulfamethoxazole, has been overcome by ex
traction into chloroform or methylene chloride.