INTRODUCTION:

Amlodipine (AMLO), chemically, 2-[(2- aminoethoxy) methyl]-4-(2-chlorophenyl)-1, 4-dihydro- 6-methyl-3, 5- pyridinedicarboxylic acid 3-ethyl, 5-methyl ester, is an anti-hypertensive and an antianginal agent in the form of the besylate salt, Amlodipine besylate. It is not official in any Pharmacopoeia. Various analytical methods have been reported for the assay of Amlodipine besylate³ in pure form as well as in pharmaceutical formulations. They include high performance liquid hromatography⁴, reversed phase high performance liquid chromatography5,6, high performance thin layer chromatography^7,8, gas chromatography⁹, gas chromatography–mass¹⁶, spectrometry¹⁰, liquid chromatography with tandem mass spectrometry¹¹ and fluorimetry¹², derivative spectroscopy^13,14,simultaneous multicomponent mode of analysis and difference spectrophotometry¹⁵ have been reported for assay of Amlodipine. However some of these methods are costlier and time consuming. To overcome these difficulties spectrophotometric analysis serves to be the quickest, promising and reliable method for routine analytical needs.

The aim of the present study is to develop a new simple, rapid, reliable and precise UV spectrophotometric method for analysis of Amlodipine from tablet formulation; method is based on measurement of UV absorbance of Amlodipine Besylate in double distilled water.

MATERIALS AND METHODS:

Apparatus:

Spectral runs were made on a Shimadzu UV-Visible spectrophotometer, model- 1700 (Japan) was employed with spectral bandwidth of 1 nm and wavelength accuracy of ± 0.3 nm with automatic wavelength corrections with a pair of 10 mm quartz cells. Glasswares used in each procedure were soaked overnight in a mixture of chromic acid and sulphuric acid rinsed thoroughly with double distilled water and dried in hot air oven.

Reagents and Solution:

All the reagents used in this assay were of analytical grade and the reagent solutions were prepared using preanalysed double distilled water. Amlodipine Besylate pure drug was obtained as a gift sample from Biochem Pharmaceutical Industries Ltd., Mumbai. Tablets of Amlodipine Besylate were purchased from local market for analysis. Double distilled water was used as a solvent for the spectrophotometric estimation.

EXPERIMENTAL:

Determination of λ max:

Weighed an accurate amount 100mg of Amlodipine Besylate was dissolved in 100ml of double distilled water to obtain a 1000mcg/ml concentration of Amlodipine Besylate in solution. This solution was subjected to scanning between 200 – 600 nm and absorption maxima at 239 nm was determined. The effect of dilution on absorption maxima was studied by diluting the above solution to 20mcg/ml and scanned from 200 – 400nm.

Standard Stock Solution:

A stock solution containing 1000mcg/ml of pure drug was prepared by dissolving accurately weighed 100mg of Amlodipine Besylate in double distilled water and volume was adjusted to 100ml with the same in 100ml volumetric flask.

Fig. 1: UV Scan of Amlodipine Besylate in double distilled water.

Table No. I: Optical characteristics and precision

Absorption maxima	239 nm
Beer's law limit	2 – 12 mcg/ml
Coefficient of Correlation	0.999933
Regression equation	Y = 0.0310X + 0.00446
Slope	0.031543
y intercept	0.00446
Molar absorptivity (lit/mole/cm)	17845.866259
Sandell's sensitivity (mcg/ Sq.cm/ 0.001)	0.031775
LOD (µg/mL)	3.046
LOQ (µg/mL)	9.232

RESULTS:

The UV scan of standard solution between 200 – 600 nm showed the absorption maxima at 239 nm, shown in fig. 1. The Beer’s law was verified from the calibration curve by plotting a graph of concentration vs absorbance. The plot is shown in fig. 2. Regression analysis showed very good correlation. The calibration plot revealed zero intercept which is clear by the regression analysis equation Y = mX + C. (Where Y is absorbance, m is the slope and X is the concentration of Amlodipine Besylate in mcg/ml) as obtained by the least square method. The results thus obtained are depicted in Table No.I. The results of analysis for assay and recovery studies for formulation were studied and are shown in Table No. II. No significant variations were observed on interday and intraday analysis. Also no significant variations were observed on changing the instrument make and model.

Fig. 2: Calibration curve of Amlodipine Besylate in double distilled water

DISCUSSION:

The spectrum of Amlodipine Besylate in double distilled water showed the absorption maxima at 239 nm. No effect of dilution was observed on the maxima, which confirmed the maxima at 239 nm. The statistical analysis of data obtained for the calibration curve of Amlodipine Besylate in pure solution indicated a high level of precision for the proposed method, as evidenced by low value of coefficient of variation. The coefficient of correlation was highly significant. The linearity range was observed between 2 – 12 mcg/ml. The plot clearly showed a straight line passing through origin (Y = 0.0310 X + 0.00446). The estimated method was validated by low values of coefficient of variation and standard error, indicating accuracy and precision of the methods. Excellent recovery studies further proves the accuracy of the method. Robustness of the method was studied by varying the instrument, time of study and analyst. Reproducibility of the results confirmed the robustness of the method.

CONCLUSIONS:

From the results and discussion the method described in this paper for the determination of Amlodipine Besylate from tablet formulation is simple, accurate, sensitive reproducible and economical. The proposed method utilizes inexpensive solvents. The proposed method could be applied for routine analysis in quality control laboratories.

ACKNOWLEDGEMENTS:

Authors are grateful to Biochem Pharmaceutical Industries Ltd., Mumbai for providing the gift sample of Amlodipine Besylate. We are also thankful to the Principal and Head of Pharmaceutical Chemistry Department of Government College of Pharmacy, Karad for providing the necessary facilities to carry out this work.

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