Chronicles of Young Scientists

: 2012  |  Volume : 3  |  Issue : 1  |  Page : 37--41

Simultaneous estimation of captopril and hydrochlorothiazide in combined dosage forms

Kareti Srinivasa Rao, Minakshi Panda, Nargesh Kumar Keshar, Sushil Kumar Yadav 
 Department of Pharmaceutical Analysis and Quality Assurance, Roland Institute of Pharmaceutical Sciences, Berhampur, Orissa, India

Correspondence Address:
Kareti Srinivasa Rao
Roland Institute of Pharmaceutical Sciences, Berhampur, Orissa - 760 010


Aim: This work deals with the simultaneous determination of captopril (CAP) and hydrochlorothiazide (HZ) in two-component solid dosage form, without prior separation, by three different techniques (simultaneous equation, absorbance ratio method, and first-order derivative method). Materials and Methods: This work was carried out on Shimadzu electron UV1800 double-beam UV-Visible spectrophotometer. The absorption spectra of reference and test solutions were carried out in 1 cm matched quartz cell over the range of 200-400 nm. Methanol and distilled water are used as solvent. Results: The first method is the application of simultaneous equation. Where the linearity ranges for both the drugs were 5-35 μg/ml. The second method is the determination of ratio of absorbance at 271 nm, the maximum absorption of HZ and isobestic wavelength 209 nm, the linearity ranges for both the drugs were 10-120 μg/ml The third method is the first-order derivative method, where the CAP shows wavelength at 222 nm and HZ shows at 340 nm, and the linearity ranges for CAP and HZ were 1-30 μg/ml and 1-40 μg/ml, respectively. The proposed procedures were successfully applied for the simultaneous determination of both the drugs in commercial tablet preparation. The validity of the proposed methods was assessed by applying the standard addition technique where the percentage recovery of the added standard was found to be 99.52±0.214 and 99.00±0.165 using the simultaneous equation method, 99.76±0.684 and 99.58±0.279 using the graphical absorbance ratio method, and 99.45±0295 and 99.21±0.678 using first derivative method, for CAP and HZ, respectively. Conclusion: The proposed procedures are rapid, simple, require no preliminary separation steps, and can be used for routine analysis of both drugs in quality control laboratories.

How to cite this article:
Rao KS, Panda M, Keshar NK, Yadav SK. Simultaneous estimation of captopril and hydrochlorothiazide in combined dosage forms.Chron Young Sci 2012;3:37-41

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Rao KS, Panda M, Keshar NK, Yadav SK. Simultaneous estimation of captopril and hydrochlorothiazide in combined dosage forms. Chron Young Sci [serial online] 2012 [cited 2019 Sep 15 ];3:37-41
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Captopril (CAP), (2S)-1-[(2S)-2-methyl-3-sulfanylpropanoyl] pyrrolidine-2-carboxylic acid, an active inhibitor of the angiotensin-converting enzyme (ACE) has been used for the treatment of hypertensive diseases [1] and moderate heart failure [2] as such or in combination with other drugs. Hydrochlorothiazide (HZ) is chemically 6-chloro-3, 4-dihydro-2H-1, 2, 4-benzothiadiazine-7-sulfonamide 1,1-dioxide. It is the prototype of the thiazide group and antihypertensive drug. [3]

Literature survey reveals that CAP was determined by several methods including spectrophotometric, [4],[5],[6],[7],[8] HPLC, [9],[10],[11] flow injection biamperometric, [12] flow injection chemiluminescence, [13] potentiometric and visual titrimetric, [14] and FT-Raman spectroscopy. [15] HZ was determined by capillary electrophoresis, [16] electrochemical study, [17] spectrophotometric, [18],[19],[20],[21],[22] and HPLC. [23],[24] Simultaneous estimation of CAP and HZ in combined dosage forms was also reported using spectrophotometric [25] and HPLC [26],[27],[28] methods. Nevertheless, the reported spectrometric method was first derivative spectrophotometric method only. The aim of this article was to explore the possibility of using techniques of simultaneous equation, the absorbance ratio (Q-analysis), and first derivative method for quantifying CAP and HZ simultaneously in their mixture forms. The proposed methods are simple, convenient, precise, accurate, and economical than the reported method.

 Materials and Methods


Instrument: This work was carried out on Shimadzu electron UV1800 double-beam UV-Visible spectrophotometer. The absorption spectra of reference and test solutions were carried out in 1 cm matched quartz cell over the range of 200-400 nm. Afcoset ER 200A electronic balance was used for weighing the samples.


Standard gift samples of captopril (CAP) and hydrochlorothiazide (HZ) were obtained from Torrent pharmaceuticals Ltd, Baddi, Himachal Pradesh. Combined CAP and HZ tablets were purchased from local market. Methanol was purchased from MERCK Ltd.


Simultaneous equation method (Method-I)

Standard stock solutions (1 mg/ml) of CAP and HZ were prepared by dissolving 100 mg of each in 20 ml methanol in a 100-ml volumetric flask and diluted to 100 ml with methanol. From this, suitable aliquots are taken and diluted with distilled water to get 10 μg/ml of CAP and 10 μg/ml of HZ. The absorption spectra of all the solutions were recorded between 200 and 400 nm. The absorbance were measured for CAP and HZ at 205 nm (λ1 ) (maximum absorbance of CAP), 271 nm (λ2 ) (maximum absorbance of HZ), and 209 nm (isobestic point). Wavelengths 205 nm and 271 nm were selected for the formation of simultaneous equation [Figure 1]. The absorbances were measured at the selected wavelengths. The molar absorptivity values were 678.5 at λ1 and 580.8 at λ2 for CAP and 898 at λ1 and 496.8 at λ2 for HZ. The absorbance and absorptivity values were substituted in the following equation to obtain the concentrations:

Cx = A 2 ay 1 - A 1 ay 2 /ax 2 ay 1 - ax 1 ay 2

Cy = A 1 ax 2 - A 2 ax 1 /ay 1 ax 2 - ay 2 ax 1

{Figure 1}

where A 1 and A 2 are absorbances of the mixture at λ1 and λ2 , respectively, ax 1 and ax 2 are absorptivity of X at λ1 and λ2 , respectively, ay 1 and ay 2 denote absorptivity of Y at λ1 and λ2 , respectively, and Cx and Cy are concentrations of CAP and HZ, respectively.

The graphical absorbance ratio method (Q-analysis method) (Method-II)

In the quantitative assay of two components by Q-analysis method, absorbances were measured at two wavelengths, one being the isobestic wavelength and the other being wavelength of maximum absorption of one of the two components. From overlain spectra of CAP and HZ, absorbances were measured at the selected wavelength, i.e., 209 nm (isobestic wavelength) and 271 nm (wavelength of maximum absorption of HZ) [Figure 1]. The concentration of each component can be calculated by mathematical treatment of the following mentioned equation.


C 1 = Qm - Qy/Qx - Qy. A 1 /a

For HZ

C 2 = Qm - Qx/Qy - Qx. A 1 /a

where, C 1 = concentration of CAP

C 2 = concentration of HZ

A 1 = absorbance of sample at isobestic wavelength (209 nm)

a = absorptivity of CAP and HZ at isobestic wavelength (209 nm)

Qx = absorptivity of CAP at 271 nm/absorptivity of CAP at 209 nm

Qy = absorptivity of HZ at 271 nm/absorptivity of HZ at 209 nm

Qm = absorptivity of sample solution at 271 nm/absorptivity of sample solution at 209 nm.

First-order derivative method (Method III)

Solutions of 10 μg/ml of CAP and HZ were prepared separately. Both the solutions were scanned in the spectrum mode from 200 to 400 nm. The absorption spectra thus obtained were derivatized from first to fourth order. First-order derivative (n=1) was selected for analysis of both the drugs. The zero crossing wavelengths 222 nm and 340 nm were selected for CAP and HZ, respectively [Figure 2].{Figure 2}

Preparation of calibration curve

Six mixed standards having concentration 1, 5, 10, 15, 20, 25, and 30 μg/ml of CAP and 1, 5, 10, 20, 30, and 40 μg ml of HZ, respectively, were prepared and scanned in the spectrum mode from 200 to 400 nm. The absorption spectra so obtained were derivatized to obtain first derivative order spectra. The absorbances of CAP and HZ were measured at 222 and 340 nm, respectively, and calibration curves of both the drugs were plotted separately. The concentration of individual drug present in the mixture was determined against calibration curve in quantitation mode.

Application of the proposed procedure for the determination of CAP and HZ in tablets

Twenty tablets were weighed, and average weight was calculated. The tablets were crushed to fine powder. The powder equivalent to 100 mg of CAP and 100 mg of HZ was transferred to 100-ml volumetric flask. The powder was dissolved in 20 ml of methanol by intermittent shaking followed by sonication for 15 min and then the volume was made up to 100 ml with methanol. The solution was then filtered through a Whitman filter paper (No. 41). The solution was diluted further with distilled water to obtain 10 μg/ml of CAP and 10 μg/ml of HZ. The concentrations of both CAP and HZ were determined by measuring the absorbance of the samples at 205 nm (λmax for CAP), 271 nm (λmax for HZ), and 209 nm (isobestic point). The recorded data were then substituted in the equation, and the results obtained are summarized in [Table 1]. The analysis procedure was repeated three times. The selectivity of the proposed procedure was examined by determining the recovery of the two drugs by standard addition method [Table 2].{Table 1}{Table 2}

 Results and Discussion

The proposed methods were found to be simple, accurate, economic, and rapid for routine simultaneous estimation of two drugs. The values of relative standard deviation are satisfactorily low, and recovery was closed to 100%, indicating reproducibility and accuracy of all methods. These methods also gave excellent result and can be used for routine analysis of these two drugs in combined dosage form.

In simultaneous equation method, the overlay spectra of CAP and HZ show overlap that prevents the use of direct absorbance measurement for determination of both the drugs in their mixture. The [Figure 1] shows that the λmax for CAP at 205 nm and for HZ at 271 nm. The absorbance curves at the selected wavelengths were found to be proportional to the corresponding concentration of the two drugs in the range of 5-35 μg/ml for both the drugs as shown by the small intercept and correlation coefficient approaching unity in the regression equation [Table 3]. The absorptivity values of the drugs were determined at selected wavelength. The absorptivity is the ratio of mean absorbance of the drug at selected wavelength with the concentration of component in mg/ml. These absorptivity values were the mean of six independent determinations. A set of two simultaneous equations obtained by using mean absorptivity values are given below

A 1 = 678.5 C CAP + 898 C HZ -------------- (at λ205 )

A 2 = 580.8 C CAP + 496.8 C HZ ------------ (at λ271 ){Table 3}

where A 1 and A 2 are absorbance of the sample at 205n and 271 nm, respectively; 678.5 and 580.8 are the absorptivity values of CAP at 205 and 271 nm, respectively; 898 and 496.8 are the absorptivity values of HZ at 205 and 271 nm, respectively; C CAP is the concentration of the CAP; and C HZ is the concentration of HZ in mg/ml.

The proposed Q-analysis method is also a simple method. In this method, the absorbances of the sample solution at the two selected wavelengths were measured and few calculations were done.

The first derivative spectrophotometry method requires spectral data processing and hence can be applied only on recording spectrophotometers with such facilities. This method was used to totally eliminate the spectral interference from one of two drugs while eliminating the other drug. This was achieved by selecting the zero crossing point on the derivative spectra of one drug as the wavelength for the estimation of other drug. First derivative method is simple, less time consuming, no manual calculation, and gives marginally better result than Q-analysis method.

Validation of methods

The methods were validated with respect to linearity, limit of detection (LOD), limit of quantification, precision, accuracy, and selectivity/sensitivity.

For linearity, the calibration plots for each method were constructed after analysis of different concentration, and each concentration was measured six times. The regression equation and correlation coefficients of the mean of six consecutive calibration curves are given in [Table 3].

LOD (k = 3.3) and LOQ (k = 10) of the methods were established according to the ICH definitions (C 1 = k S 0 /s), where C 1 is LOD or LOQ, S 0 is the standard error of blank determination, s is the slope of the standard curve, and k is the constant related to the confidence interval. The LOD, LOQ, and standard error of the methods are given in [Table 3].

Accuracy was investigated by analyzing three different concentrations of combined dosage form of CAP and HZ in linear range in six independent replicates. The data evaluated using equations are summarized in [Table 4]. Accuracy was expressed as bias (%). The bias values were close to zero [Table 4]. The relative standard deviation (RSD) values and also the low RSD values obtained from the analysis of pharmaceutical formulations indicated that the intermediate precision of the method was good.{Table 4}


The proposed method based on simultaneous equation, graphical absorbance ratio, and first-order derivative methods can be used for the simultaneous determination of CAP and HZ either in their combined dosage form or alone in their tablet preparation. The proposed methods are precise, accurate, and simple to perform. Also, no separation step is required. Hence, the proposed methods can be used for the routine analysis of CAP and HZ.


The authors are thankful to Roland Institute of Pharmaceutical Sciences, Berhampur, Orissa, for providing necessary facilities.


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