Estimation of Metoprolol Tartrate and Chlorthalidone in Combined Dosage Form by UV-Spectrophotometric Methods


Raval H.R.*, Patel D.M. and Patel C.N.

Department of Quality Assurance, Shri Sarvajanik Pharmacy College, Mehsana-348001, India

*Corresponding Author E-mail:



Two simple, sensitive, rapid and precise UV spectrophotometric methods have been developed and validated for simultaneous estimation of Metoprolol Tartrate and Chlorthalidone. Recently this combination was approved for the treatment of patients with mild to moderate essential hypertension which is available in tablet dosage form. The first method is simultaneous equation method in which wavelength selected for estimation of Metoprolol Tartrate and Chlorthalidone are 275 nm and 284 nm, respectively. The second method is first order derivative method based on measurement at zero crossover point of another drug. Measurement of Metoprolol Tartrate and Chlorthalidone were carried out at 270.5 nm and 280.8 nm, respectively. The linearity was obtained in the concentration range of 25-200 µg/ml for Metoprolol Tartrate and 25-200 µg/ml for Chlorthalidone. The proposed methods are successfully applied for the simultaneous determination of both drugs in synthetic mixture. The method was validated with respect to linearity, accuracy and precision as per the International Conference on Harmonisation (ICH) guidelines.


KEYWORDS: Metoprolol tartrate, Chlorthalidone, simultaneous equation, first order derivative.




Chlorthalidone (CHL), chemically (RS)-2-chloro-5-(1-hydroxy-3-oxo-2,3-dihydro-1H-isoindol-1-yl) benzene-1-sulfonamide, is a thiazide type diuretics that is used in the treatment of hypertension and edema. Metoprolol Tartrate (MET), chemically (RS)-1-(Isopropylamino)-3-[4-(2 methoxyethyl) phenoxy] propan-2-ol, is a selective β1 receptor blocker used in the treatment of several diseases of the cardiovascular system, especially hypertension1-2. Recently this combination has been approved for the treatment of patients with mild to moderate essential hypertension in tablet dosage form.


Both the drugs are official in Indian Pharmacopoeia (IP), British Pharmacopoeia (BP) and United State Pharmacopoeia (USP). Potentiometry is the official method for both the drugs in IP3 and BP4 while HPLC is official method in USP5. Literature review revealed many other Spectrophotometric6-11, HPLC12-18, HPTLC19-20, GC-MS21 and Fluorimetric22 methods for estimation of MET and CHL individually and combination with other drugs.


To the best of our knowledge, no study has been described for the simultaneous determination of both the drugs in combined dosage form by UV spectrophotometric method. The present paper describes two simple, rapid and economic methods namely simultaneous equation method and first order derivative method for simultaneous estimation of MET and CHL. The proposed methods were validated as per International Conference on Harmonization (ICH) guidelines Q2 (R1).




The Shimadzu UV-Visible Spectrophotometer model 1700 was employed. The sample solution was recorded in 1 cm quartz cell against solvent blank over the range of 200-400 nm. The optimal condition for recording the spectra to achieve good reproducibility include, medium  scan speed and slit width at 2 nm.



Pure drug samples of MET and CHL were procured from Yarrow Chem Products, Mumbai, India and were used as received. All analytical grade chemicals and solvents used were procured from Loba Chemicals Pvt. Ltd., Mumbai, India.


Preparation of standard solutions and calibration curve:

Stock solutions for spectrophotometric measurements were prepared by dissolving MET and CHL in methanol to obtain concentration of 1 mg/ml.  Aliquots of the standard stock solution were transferred to a series of 10 ml volumetric flask and suitability diluted with methanol to give varying concentrations ranging from 25-200 µg/ml for MET and 25-200 µg/ml for CHL. The solutions were scanned in the wavelength range of 200-400 nm.


Preparation of sample solution:

Twenty tablets were weighed, powdered and accurately weighed quantity of powder equivalent to labelled claim of MET and CHL both were transferred to a 100 ml volumetric flask and dissolved in 50 ml of methanol by ultra-sonication for 20 min. The solution was diluted with same solvent and filtered through whatmann No.41 filter paper. The filtrate was diluted with methanol to get final dilution of 50 and 25 µg/ml for MET and CHL, respectively.


Method I: Simultaneous equation method:

From overlain spectra; two wavelengths selected were 275 nm for MET and 284 nm for CHL (Figure 1). A1%, 1 cm was calculated for each drug from absorbance values for the drug at selected wavelengths. Simultaneous equations were constructed from calculated absorptivity values.


Absorbance of sample solution was measured at selected wavelengths as A1 and A2 and concentration of the two drugs in sample was calculated by using following equation.


Where; A1 and A2 are the absorbances of mixture at 275nm and 284 nm,  respectively; ax1 and ax2 are absorptivities of MET at 275nm and 284 nm, respectively; ay1 and ay2 are absorptivities of CHL at 284 nm and 275 nm, respectively.


Figure 1: Overlain zero order spectra of Metoprolol Tartrate (50 µg/ml) and Chlorthalidone (25 µg/ml)


Method II: First-order derivative spectroscopy:

The spectra obtained in method I were derivatised to obtain first derivative spectra. The two spectra were overlain. It appeared that MET showed zero crossing at 270.5 nm while CHL showed zero crossing at 281.8 nm. At the zero crossing point of MET (270.5 nm), CHL showed a substantial dA/dλ, whereas at the zero crossing point of CHL (281.8 nm), MET showed a substantial dA/dλ. Hence the wavelengths 270.5 nm and 281.8 nm were selected as analytical wavelengths for determination of MET and CHL, respectively. These two wavelengths can be employed for the estimation of MET and CHL without any interference from the other drugs in their combined formulation. Calibration curves were plotted by taking dA/dλ on Y-axis and concentrations on X-axis. Spectrum of sample also derivatised and absorbance of both the drugs were measured at selected wavelengths and concentrations were calculated from calibration curves.


Figure 2: Overlain first order derivative spectra of Metoprolol Tartrate and Chlorthalidone



Metoprolol Tartrate was soluble in water but Chlorthalidone was practically insoluble in water. Both drugs were soluble in methanol; hence methanol was selected as solvent. Figure 1 shows overlain zero-order spectra of MET and CHL at 50 and25 μg/ml, respectively that showed λmax of 275 nm and 284 nm for MET and CHL, respectively. Also, each of which absorbs at the λmax of the other hence, simultaneous equation method was used to estimate MET and CHL in presence of each other. While in first order derivative method (Figure-2), measurement of both drugs is possible without interference of each other. Both the methods were validated statistically as per ICH guideline for parameters like linearity, precision and accuracy. The values of coefficient of variation were satisfactorily low. Accuracy was performed by recovery study at three level 80%, 100%, and 120% of the test concentration. The RSD values for intraday and interday precision are less than 2%. The recovery was between 98-102%.  All data are as shown in Table 1. The amounts in terms of % label claim obtained by proposed methods are presented in Table 2.



The described methods give accurate and precise results for determination of MET and CHL mixture in pharmaceutical dosage form. The method was found to be simple, accurate, economical, reproducible and rapid. Hence, it can be employed for routine analysis.

Table 1: Statistical parameters


Method I

Method II





Regression Equation

Y = 0.1025x  + 0.0169

Y = 0.0448x  +  0.0048

Y = 0.003x + 0.000

Y = 0.001x  -  0.000

Correlation  Co-efficient





Precision (%RSD)


0.29 - 0.62 %

0.27 – 0.60 %

0.12 - 0.65 %

0.34 - 0.66 %


0.38 – 0.64 %

0.36 – 0.54 %

0.34 - 0.86 %

0.69 - 1.24 %


98.27  – 101.97 %

99.20 – 102.66 %.

99.06  – 100.88 %

100.14  – 101.24 %


Table 2: Analysis of Tablet formulation



Label claim

% Label claim estimated

(mean   ±  S.D.)*

Simultaneous equation method (Method I)


25 mg



12.5 mg

103.02±1.04 %

First order derivative (Method II)


25 mg

99.80 ±0.60 %






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Received on 09.04.2011       Modified on 29.04.2011

Accepted on 18.05.2011      © RJPT All right reserved

Research J. Pharm. and Tech. 4(8): Aug. 2011; Page 1204-1206