Spectrophotometric Estimation of Amoxicillin Trihydrate in Bulk and Pharmaceutical Dosage Form

New simple, sensitive, rapid, reproducible and economical spectrophotometric method have been developed for the determination of amoxicillin trihydrate in pharmaceutical bulk and tablet dosage form using citro phosphate buffer pH 7.2. The system obeys Lambert-Beer’s law at 231 nm in the concentration range 2.5-50 μg/m. Molar absorptivity, correlation coefficient and Sandell’s sensitivity values were found to be 1.0020 x 10 mol cm, 0.9996 and 0.03906 μg cm respectively. The proposed methods have been successfully applied to the analysis of the bulk drug and its tablet dosage form. The methods have been statistically evaluated and were found to be precise and accurate


Instrument
All the spectral and absorbance measurements were made on an ELICO SL-59, UV-VIS spectrophotometer by using 1 cm match quartz cells.

Materials
Amoxicillin trihydrate used in the present investigation is obtained from Tini Pharma Ltd, Renigunta, Tirupati.Disodium hydrogen phosphate and citric acid were purchased from local market.

Mathods
An accurately weighed amount of amoxicillin trihydrate equivalent to 100 mg was transferred in to 100 mL volumetric flask.To this 50 mL of citro phosphate buffer pH 7.2 was added, sonicated for 10 minutes, shaken thoroughly for 15 minutes and then made the volume with citro phosphate buffer pH 7.4.Filter and further dilutions were made with citro phosphate buffer pH7.2.A series of standard solutions containing 2.5-50 µg/mL of amoxicillin trihydrate were prepared in citro phosphate buffer pH 7.2 and absorbences were measured at 231 nm against solvent blank.The samples were stored at room temperature and again absorbances were measured after 48 hrs that indicates amoxicillin trihydrate is stable in the citro phosphate buffer pH 7.2.

Estimation of amoxicillin trihydrate in pharmaceutical formulations (Tablets, capsules, suspension and syrup)
An accurately weighed amount of tablets, capsules, suspension and syrup are transferred in to a 50 mL volumetric flask and to this 25 mL of citro phosphate buffer pH 7.2 was added, sonicated for 10 minutes, shaken thoroughly for 15 minutes and then made the volume with citro phosphate buffer pH 7.2.Filter and further dilutions were made with citro phosphate buffer pH 7.2.The absorbances of these solutions were measured at 231 nm against solvent blank.

Results and discussion
Beer's law was obeyed in the concentration of 2.5-50 µg/mL in the proposed method.The optical characteristics are summarized in Table 1 The effect of different parameters was studied and optimum conditions were included.Sandell's sensitivity of 0.03906 µg/cm 2 /0.001 absorbance unit showed that the proposed method was quite sensitive.Linear regression of absorbance on concentration gave the equation Y=0.0012+0.0244C where C is the concentration in µg/mL and Y is the absorbance at 231 nm with a correlation co-efficient of r = 0.9996.This indicates a good linear relation ship.The values obtained for the determination of amoxicillin trihydrate in several pharmaceutical formulations (Tablets, capsules, suspension and syrup) by the proposed method are given in Table 2. To evaluate the validity and reproducibility of the method known amounts of pure drug was added to previously analyzed pharmaceutical preparations and the mixtures analyzed by proposed method and the percent recoveries are given in Table 2.The results showed that the proposed method has reasonable precision and accuracy.

Conclusion
The developed method was found to be sensitive, accurate, precise and reproducible and could be used for the routine estimation of amoxicillin trihydrate in bulk and pharmaceutical formulations.

Table 1 .
. Validation * = b+ a C, where "C" is concentration in µg/mL and Y is absorbance unit.

Table 2 .
Estimation of amoxicillin trihydrate in marketed formulations