Spectrophotometric Determination of Atenolol Using Indigo Carmine Dye

A simple, rapid, accurate and precise spectrophotometric method is proposed for the determination of atenolol in both pure form and in its pharmaceutical formulation. The method is based on the oxidation of atenolol with chromate in acidic medium of 1N H2SO4, the residual amount of oxidizing agent is then reacted with indigo carmine dye in the presence of oxalate as a catalyst, the increase in the absorbance of the dye, which is proportional to the amount of the determinants atenolol is then measured at 610 nm. Beer's law is obeyed in the concentration range of 30-1500 μg/25 ml with a molar absorptivity of 0.73×10 4 l.mol -1 .cm -1 , Sandell's sensitivity index of 0.364 μg.cm -2 , and a relative standard deviation of ± 0.263 to ± 0.376% depending on the concentration level. The limit of detection (LOD) and limit of quantification (LOQ) are 0.3259 and 1.0863 μg ml −1 , respectively. The proposed method has been applied successfully to the determination of atenolol in pure and pharmaceutical preparation.


Introduction:
Atenolol, ATN (Scheme 1) is a cardioselective β-blocker antagonist, chemically known as 2- {4-[2-hydroxy-3-(propan-2-ylamino) propoxy] phenyl} acetamide [1]. ATN is used to treat chest pain (angina) and high blood pressure (hypertension). hypertension is also used to decrease the severity of heart attacks and control of some forms of cardiac arrhythmia and for the management of hypertension, prevention of chest pain. It may be used alone or concomitantly with other antihypertensive agents including thiazide-type diuretics, hydralazine, prazosin and αmethyldopa. [2][3][4] A spectrophotometric method has been proposed for the determination of ATN using cerium Furthermore, I.C. used as a food colorant and also as a dye in the manufacturing of capsules [24]. Spectral and absorbance measurements are carried out using JASCO V -630 UV-Visible computerized double-beam spectrophotometer. In all measurements, matched cells of 1 cm are used. The pH measurements are carried out using HANA pH meter.

Reagents And Materials:
All chemicals used are of analytical reagent grade.

Atenolol (1000 μg/ ml) solution:
This solution was prepared by dissolving 0. 1000 g of atenolol in distilled water and the volume was completed to 100 ml with distilled water in a volumetric flask. The solution was then transferred to a dark bottle in order to be stable for at least 2 days. Working solution of 100 μg/ml atenolol solution was prepared by appropriate dilution of the stock solution with distilled water.

Chromate solution, (8.6×10 -4 M) solution:
This solution is prepared by dissolving 0.0167 g of potassium chromate (Fluka) in 100 ml distilled water in a volumetric flask. The solution was transferred to a dark bottle and it is stable for at least one month.

Indigo Carmine, (1×10 -3 M) solution:
This solution is prepared by dissolving 0.1165 g of indigo carmine (BDH) indistilled water, then the volume is completed to 250 ml with distilled water in a volumetric flask. This solution is stable for at least 3 days.

Sodium oxalate solution, 0. 1 M:
This solution is prepared by dissolving 1.34 g of sodium oxalate (Fluka) in distilled water then is the volume completed to the mark with distilled water in a 100-ml volumetric flask.
Sulphuric acid solution, 1N. This solution is prepared by appropriate dilution of concentrated sulphuric acid solution to the mark with distilled water in a 250-ml volumetric flask.

Study of optimum conditions:
The effect of various parameters on the oxidation-reduction reaction and the intensity of the coloured complex has been studied and optimum conditions have been selected.

Effect of sulphuric acid amount
In order to choose the optimum amount of sulphuric acid for the reaction of chromate with atenolol and indigo carmine, different amounts (0-3.5) ml of sulphuric acid solution (1N) are tested. The results are shown in Fig.1

Effect of oxalate ion amount
Oxalate usually served a promoting activator or catalyst for

Effect of Indigo carmine amount
The effect of the amount of indigo carmine dye on the absorbance of the reaction mixture is investigated. It was found from the experimental results that 1.0 ml of indigo carmine reagent 1.0×10 -3 M was optimum (determination coefficient =0.995441), and recommended for the subsequent experiments as shown in Table 2.

Effect of order of addition:
The different orders of addition were studied. The results shown in Table 3 indicate that the first order was optimum because it gives highest absorbance value and best stability (because it is the best order of addition that make Cr(VI) react with At then the residual of it react with I.C), therefore it is selected for the subsequent experiments.

Development time and stability period:
To test the effect of time on the absorbance for different amounts of ATN at the wavelength of maximum absorption at 610 nm, under the optimum experimental conditions, the absorbances were measured at different intervals of time. The experimental results are shown in Fig.3 indicating that maximum absorbance is obtained immediately and remains constant for at least 2 hours.

Absorption spectra and calibration graph:
When atenolol is treated according to the recommended procedure, the absorption spectra and calibration graph are shown in Fig.4

Accuracy and precision:
To check the accuracy and precision of the calibration curve, ATN is determined at three concentrations. The results shown in Table 4 indicate that these are reliable.

Nature of the reactions:
Job's method of continuous variations has been used in the determination of the reaction ratio of atenolol with chromate. The obtained results Fig. 6 showed that the ratios of atenolol to chromate is 1:1. As a result the following reaction is suggested:

Effect of interferences:
In order to test the efficiency and selectivity of the proposed method, the effect of some foreign substances (e.g., acacia, glucose, lactose, menthol and starch) that are usually present in dosage forms were studied by adding different amounts of foreign substances to 100 μg atenolol/25 ml. It was observed that the studied foreign species did not interfere in the present method Table 5.

Application of the method:
The proposed method was successfully applied to the determination of ATN in its pharmaceutical preparation (tablet). The results which are shown in Table 7 indicate that good recoveries were obtained.  Table 8.  Table 9 shows the comparison between some of analytical variables for the present method with that of other literature spectrophotometric methods.  The results indicate that the proposed method is sensitive and can be applied successfully to the determination of atenolol in pharmaceutical preparation.