Extractive Spectrophotometric Methods for the Determination of Enalapril Maleate in Tablets


Avadhut T. Phadatare, Santosh R. Karajgi, Gopinath S. Dashrathe and N.V Kalyane

Department of Pharmaceutical Chemistry, B.L.D.E.A’s College Of Pharmacy Bijapur, Karnataka, 586103 India.

*Corresponding Author E-mail: avadhutphadtare1@gmail.com



A simple, rapid, sensitive, precise and economic spectrophotometric method has been developed for the estimation of Enalapril maleate (ENA) in tablet formulation. During the course of study, it was observed that basic solution of the drug formed ion pair complex with Thymolphthaline (THP) which were soluble in chloroform. This property of the drug was followed for the development of colorimetric methods for analysis of drug. The complex of ENA with THP showed λmax at 475 nm. This method was validated statistically. Recovery studies gave satisfactory results indicating that none of common additives and excipients interfere the assay method. The proposed method is found to be simple, accurate and reproducible that was successfully applied for the analysis of tablet formulation.


KEYWORDS: Enalapril maleate, Colorimetric analysis, FG FCF, THP, Extractive spectrophotometry,




Enalapril maleate is described chemically as (2S)-1-[(2S)-2-[[(2R)-1-ethoxy-1-oxo-4-phenylbutan-2-yl]amino]propanoyl]pyrrolidine-2-carboxylic acid. Is a angiotensin-converting enzyme inhibitor widely used in the treatment of   hypertension and heart failure. Its empirical formula is C20H28N2O5 & its structural formula fig.1. Spectrophotometric and AAS1, LC & LC-MS & a validated stability-indicating assay method2, spectrophotometic methods3-5 for the estimation of enalapril maleate alone or in combination with other antihypertensive agent simultaneous equation spectrophotometric and HPLC6.



Materials and Methods:-

A.      Materials:-

Standerd drug Enalapril      Thymolophthaline

double distilled water          Chloroform (AR grade)

Instrument: A Elico UV double beam spectrophotometer with 1 cm matched quartz cells was used for the estimation

B.       Method:-

Elico double beam U.V. spectrophotometer with 1 cm matched quartz cells. All reagents used were of analytical grade. Following reagents and solutions were used.

Preparation of buffer pH 11:- place 50ml of 0.210 gm of sodium bicarbonate add 22.7ml of 0.1 M NaOH and then add water to make a volume 100ml.


Preparation of THP Solution: dissolve 50 mg of Thymolphthaline in 0.92 ml of 0.1M NaOH and 20ml ethanol (95%) solution is effected and sufficient water to produce 100ml.


Standard drug solutions:

A. A stock solution of drug is prepared by dissolving accurately weighed 50 mg of pure Ramipril in 50 ml of water. So as to give the stock solution A of concentration 1 mg/ml.

B. 5 ml of stock solution-A was pipetted in to a 50 ml volumetric flask and was diluted to 50 ml with water to give stock solution–B. of concentration 100 mcg/ml.

C. Sample solution (capsule): Twenty capsules were taken and average weight was calculated. Capsule powder equivalent to 100 mg of drug was weighed accurately and transferred to 100 ml volumetric flask. Water was added to the flask and the contents were shaken well for 10 minute and the volume was made up with water. This was filtered; rejecting the first few ml of filtrate, 5 ml of the filtrate was pipetted into 50 ml flask and was diluted to the mark. From this 5 ml was pipette into 25 ml flask, 5 ml of the reagent, 5 ml of buffer was added and the volume made up with chloroform.



From solution–B 1.5, 3.0, 4.5, 6.0, 7.5 ml was pipetted in to 5 separate separating funnel, and 20 ml of chloroform, 5 ml of buffer and 5 ml of THP were added. The contents were shaken for two minutes and the two phases were allowed to separate. The lower chloroform layer was collected in separate 50 ml volumetric flasks. The aqueous phase was further extracted two times with 10 ml portions of chloroform. The chloroform layer was combined and the volume was made up with chloroform so the concentration of the drug would be 3, 6, 9, 12, 15 mcg/ml. the absorbance was measured at 475 nm against blank solution obtained in the same way omitting the drug.


Fig.1.Sructural formula of Enalapril maleate



The amount of Enalapril maleate present in the sample was computed from the calibration curve results are reported in tables I and II. The proposed method is colorimetric method for determination of Enalapril maleate from bulk powder and formulations. This method is very simple, accurate and sensitive give reproducible results. Proposed method can be used for determination of Enalapril maleate in bulk powder and formulations in a routine manner.


Table-I: Optical Characteristics and Other Parameters


Enalapril maleate With THP

λmax (nm)


Beer’s Law limits (mcg/ml)


Molar absorptivity

5218.2 mol-1cm-1

Standard deviation


Coefficient of variation (%)

0.5829 %


Table-II: Results of the Estimation of Enalapril Maleate In Tablets using THP.

Formul ation

Claim (mg/ cap)

Amount of pure drug added (mg)

Content determined in Assay (mg)

% reco very








The proposed methods are simple, sensitive, accurate and economical for the routine estimation of Enalapril maleate in bulk and in its tablet dosage form.




The authors wish to thanks Dr.Navnath Kalyane, Principal of B.L.D.E.A’S College of Pharmacy for providing laboratory facilities & Piramal healthcare Ltd. Baddi for providing Enalapril maleate as gift sample.



1.        British Pharmacopoeia (2008) M. Stationary Off Lond I:794

2.        Ayad Magda M., Shalaby Abdalla A., Abdellatef Hisham E., Hosny Mervat M. “Spectrophotometric and AAS determination of ramipril and enalapril through ternary complex formulation.” J Pharm Biomed Ana 2002; 28:311-21.

3.        Singh Saranjit, Bharadwaj Sunny Piyush, “Study of forced degredation behaviour of enalapril maleate by Lc and LC-MS and development of a validated stability-indicating assay method”. J Pharm Biomed Ana 2008; 46:113-20..

4.        Walily abdel Fattah M. El., Belal Saeid F., Heaba Eman A., Kersh Ali El, “Simultaneous   determination of enalapril maleate and hydrochlorthiazide by first- derivative ultraviolet spectrophotometry and high-performance liquid chromatography”. J Pharm Biomed Ana 1995;13:851-56.

5.        Rahman N. and Haque S. M. Optimized and Validated Spectrophotometric Methods for the Determination of Enalapril Maleate in Commercial Dosage Forms. Ana Chem Insights, 2008;3:31-43.

6.        Thomas A. B., Chaudhari A. A., Nanda R. K., Kothapalli L.P., Chavan U. B., Deshpande A.D., “Simultaneous Determination of Enalapril and Losartan in Pharmaceutical Preparations by UV Spectrophotometry and LC”. J Chromatographia 2009;69:1-3






Received on 17.02.2011          Modified on 03.03.2011

Accepted on 20.03.2011         © RJPT All right reserved

Research J. Pharm. and Tech. 4(5): May 2011; Page 825-826