INTRODUCTION:

Telmisartan is 4’-[1, 4’-dimethyl-2-propyl [2, 6’-bi-benzimidazole]-1’-yl] methyl 1, 1’- biphenyl 2-carboxylic acid. Telmiartan is practically insoluble in water; sparingly soluble in strong acid; soluble in strong bases.1,2 It blocks the vasoconstrictor and aldosterone secreting effects of angiotensin II by selectively blocking the binding of angiotensin II to the AT1 receptor in many tissues, such as vascular smooth muscle and the adrenal gland ^1-2.(Fig. 1).

Fig.No.1.Structure of Telmisartan

Literature survey reveals that several spectroscopic and chromatographic methods for analysis of Telmisartan in different dosage form like colorimetric,³ U.V^4-8,UV and RP-HPLC^9,10, RPHPLC^11-22, RPHPLC and HPTLC²³RPHPLCCoupled with Tandem Mass Spectrometry,²⁴UPLC ²⁵, HPLC ^26-28 were reported.

Our main concern is development and validation of UV spectrophotometric method as per ICH guideline.

MATERIALS AND METHODS:

Apparatus

A Shimadzu UV/Visible double beam spectrophotometer (Model 1700) with 1 cm matched quartz cells were used in present study for spectral and absorbance measurements.

Reagents and Materials

All reagents used were of analytical grade and double distilled water was used throughout the investigation.

· Azur-B Reagent: Dye solution (0.1% w/v) was prepared in Distilled water.

· Standard Stock Solution: Accurately weighed (50 mg) pure drug sample of Telmisartan was transferred to 50 ml calibrated volumetric flask, dissolved and made up to the mark with 0.1 N NaoH solution , Further 1.0 ml of stock solution was diluted to 100 ml.(10 μg/ml)

Table 1: Quantitative parameters of spectrophotometric method

Parameters	Method
λ_max,nm	508.00
Beer’s law limits, µg/ml	2-10
Molar absorptivity, l mol^-1 cm^-1	1.7756
Regression equation	y = 0.0804x + 1.528
Slope	0.0804
Intercept	1.528
Correlation coefficient (r²)	0.9875
SD	0.3527

Methodology

Different aliquots (0.2, 0.4, 0.6, 0.8 and 1.0 ml) of a standard Telmisartan (10 μg/ml) solution were transferred into a series of 10 ml calibrated flasks and all were made up to the mark with 0.1 N NaoH solution. To the above solution, 5 ml of Azur-B reagent was added in a separating funnel. Reaction mixture was shaken gently for 5 min and allowed to stand so as to separate the aqueous and chloroform layer. Coloured chloroform layer was separated out and absorbance was measured at 508 nm against reagent blank. A calibration curve was plotted from the absorbance values so obtained. A representative spectra and calibration curve of ion pair complex of Telmisartan and Orange II dye is reported in fig 1 and fig 2 respectively.

Fig. 2: Spectra of ion pair complex of Telmisartan and Azur-B dye

Fig. 3: Calibration curve of ion pair complex of Telmisartan and Azur-B dye

Analysis of Tablet Formulation

Twenty Tablets were weighed accurately and ground into fine powder. An amount of the powder equivalent to 50 mg of Telmisartan was weighed and dissolved in about 50 ml 0.1 N NaoH solution. The solution was shaken thoroughly for about 15-20 min, and filtered using Whatman No. 41 filter paper; residue was washed with 20 ml NaoH solution. Filtrate and washing were transferred to a 100 ml calibrated volumetric flask and 0.1 N NaoH solution was added up to the mark. Filtrate 1 ml was diluted to 100 ml with 0.1 N NaoH solution. These final dilutions were treated as per the procedure for respective calibration curve. Absorbance was measured at respective wavelength maxima and the concentration of the drug in sample solution was determined from calibration curve. Results of analysis are presented in Table 2.

The optical characteristics such as Beer’s law limit, molar absorptivity were calculated and summarized in Table 1. Regression equation, correlation coefficient, slope and intercept are also shown in Table 1.

Recovery Studies

Recovery studies were carried out by addition of pure drug to previously analysed Tablet sample at three different concentration levels. The results of recovery studies are reported in Table 2. The results of recovery studies reflect that there is no interference of excipients in the analysis of Telmisartan from Tablet formulation.

RESULT AND DISCUSSION:

A colorimetric method has been developed for the quantitative estimation of Telmisartan from Tablet formulation. The developed methods are based on the formation of ion pair complex of drug with Azurin-B Dye. The results of analysis from Tablet formulation were within the permissible limits and the results of recovery studies reflect nil interference from excipients. The developed methods were found to be simple, accurate and economical hence can be used for routine analysis of Telmisartan from pharmaceuticals.

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Received on 28.04.2014 Accepted on 26.05.2014

Asian J. Pharm. Ana. 4(2): April-June 2014; Page 54-56