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Practical : Assay of an Aspirin tablet by UV spectrophotometer

Introduction:

Aspirin is widely used as alagesic and anti-inflammatory agents. Its activity as antiplatelet agent is also well know. In aquous solution when aspirin is heated with NaOH, it is converted to salicylate ion which form a colored complex with FeCl3. The intensity of the color is directly related to the concentration of acetyl salicylic acid present. A series of standard solutions with different acetyl salicylic acid concentrations will be prepared and complexed. The absorbance of each solution will be measured and a calibration curve will be constructed. Using the standard curve, the amount of aspirin in a commercially available aspirin tablet can be determined.

Purpose:

To analyse a commercially available aspirin tablet in order to ascertain its acetyl salicylic acid content.

Equipment / Materials:

125 mL conical flasks, cuvettes, measuring cylinder (50 ml), 1ml pipette, 100 mL volumetric flask, standard acetylsalicylic acid, 50 mL volumetric flask, 1 M NaOH, balance (4 digit.), 0.02 M FeCl3 solution, spectrophotometer, distilled water and aspirin tablet

Procedure:

Preparation of stardard solutions
1. Weigh out 200 mg of acetylsalicylic acid and place in a 125 mL conical flask. Add 5 mL of a 1 M NaOH solution to the flask, and heat until its contents start boiling.
2. Transfer the above solution carefully to a 100 mL volumetric flask. Wash the flask with distilled water and pour into the volumetric flask. Add distilled water upto the mark. This is the stock solution.
3. Uning 1ml pipette, transfer 0.5, 1, 1.5, 2 and 2.5 ml from the stock solution to five different 50ml volumetric flasks labeled as S-1, S-2, S-3, S-4 and S-5. Make up the volume each of the volumetric flasks by adding 0.02 M FeCl3 solution.

Preparation of sample solutions
1. Ground an aspirin tablet using mortar and pestle. Weigh out amount equivalent to 200mg of acetylsalicylic acid in a 125 mL conical flask. Add 5 mL of a 1 M NaOH solution to the flask, and heat until the contents begin to boil.
2. Transfer the above solution carefully to a 100 mL volumetric flask. Wash the flask with distilled water and pour into the volumetric flask. Add distilled water upto the mark.
3. Transfer 1.5 ml of above solution into 50ml volumetric flask. Dilute to the mark by adding 0.02 M FeCl3 solution. This is sample solution.
Measurement of absorbance
1. Adjust the spectrophotometer to the wavelength to 530 nm.
2. Insert the blank (0.02 M FeCl3 solution) into the cell holder and adjust the reading to zero. Remember to wipe off the cuvet with a tissue before inserting it into the instrument.
3. Measure the absorbances of each of the FIVE standard solutions, starting from the lowest concentration.
4. Measure the absorbance reading for the unknown sample.
5. Plot concentration (x-axis) vs. absorbance (y-axis) of standard samples on graph paper. Draw a straight line passing through most of the points.
6. From the standard curve, determine the concentration of the unknown diluted sample and convert it to mg/ml.
7. Determine the amount of acetyl salicylic acid present in ~325 mg aspirin tablet by using following equation,
A=(Conc of diluted sample) X (dilution factor) X 100.
Amount of acetylsalicylic acid present in the tablet, A= amount calculated from curve X (501.5) X 100

8. Amount of acetyl salicylic acid in each tablet, B = (A÷X)X 300 where X is the weight of ASPIRIN tablet in mg
9. % error= (300-B)/300 X100

Spectrophotometric Analysis of Aspirin Standards Data
Data:
Solution, Concentration (ug/ml), Absorbance
Standard 1 0.5 ml 0.134 nm
Standard 2 1 ml 0.275 nm
Standard 3 1.5 ml 0.439 nm
Standard 4 2 ml 0.576 nm
Standard 5 2.5 ml 0.860 nm
Sample 1.5 ml 0.273 nm

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Practical: Assay of an Aspirin tablet by UV spectrophotometer
1. Abstract
The purpose of the experiment is to analyze a commercially available aspirin tablet in order to ascertain its acetylsalicylic acid content. UV spectroscopy is a very useful method for quantitative analysis of drug substance. A standard calibration curve is used to determine the amount of aspirin in a commercial tablet. In 325 mg commercial tablet was estimated to have 292.5 mg which is equivalent to 270 mg for 300 mg. The % error in the analysis was determined to be 10%.
2. Introduction:
The purpose of the experiment is to analyze a commercially available aspirin tablet in order to ascertain its acetylsalicylic acid content.1 Aspirin is a non-steroidal anti-inflammatory drug (NSAIDs) which is used as a painkiller and originally discovered from salicylic acid known to have irritant to GIT and several undesirable side effects. It is a COX inhibitor, and the side effect is also attributed due to non-selectivity between COX-1 and COX-2 inhibition. Aspirin is chemically called by the name of acetylsalicylic acid. It is an ester of salicylic acid, which is prepared by the reaction of salicylic acid with acetic anhydride.2

In principle, UV spectroscopy depends on absorption of UV-Vis radiation which is directly proportional to concentration (Beer’s Lambert’ Law).

A = abc

Where A = absorbance
a = molar absorptivity
b = path length
c =concentration
An aqueous sodium hydroxide solution of aspirin was prepared which converted it to salicylate ion. Ferric chloride (FeCl3) solution was used to form the color complex with salicylate ion, and its intensity is directly proportional to the concentration of salicylic acid or aspirin. A standard calibration curve was prepared by serial dilution which can be used to find out the amount of aspirin in a tablet....
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