Spectrophotometric determination of trimethoprim in pure form and pharmaceutical preparations using tropeolin oo and 2,3-dicloro-5,6-dicyano -p-benzoquinone

Nawal A. Alarfaj*, Salma. A. Altamimi and Latifa Z. Almarshady

Chemistry Department, College of Science, Women Student Medical Studies and Science Section, King Saud University, P.O.Box 22452, Riyadh - 114 95 (Saudi Arabia)

ABSTRACT: Two simple and sensitive specrophotometric methods are described for the quantitative determination of trimethoprim (TMP) in pure forms as well as in its pharmaceutical formulations. The first method (Method – A) is based on the formation of an ion association complex between the drug and an acidic dye, tropaeolin OO (TPOO), which is extractable into chloroform. A violet colour, peaking at 540 nm was produced and its absorbance is linear with the concentration over the range 2.9-13.3 μg ml-1 with correlation coefficient (n=6) of 0.9998. The second method (Method – B) is subjected to charge transfer complexation reaction with 2,3-dicloro-5,6-Dicyano-p-benzoquinone (DDQ) as a p-electron acceptor. A redish brown colour peaking at 458 nm was obtained and its absorbance is linear with concentration over the range 5-130μg ml-1 with correlation cofficient (n=8) of 0.9998. All variables in these methods are optimized. No interferences were observed from pharmaceutical formulations additives and the applicability of the methods was examined by analyzing pharmaceutical formulations containing TMP. The quantities determined were 98.5-101.6% of the expected value.

KEYWORDS: Trimethoprin; Ion association; charge transfer complexes

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