Name of the Experiment: Determination of the potency of Paracetamol (Napa) tablet (Beximco Company) by UV-Spectrophotometric method.

Principle:

When a beam of radiation (light) passes through a substance or a solution, some of the light may be absorbed and the remainder transmitted through the sample. The ratio of the intensity of the light entering the sample (Io) to that exiting the sample (I) at a particular wavelength is defined as the transmittance (T). The absorbance (A) of a sample is the negative logarithm of the transmittance.

A = - log (T)

Figure: Absorption of light by a sample

Beer-Lambert LawThe absorbance of a sample at a given wavelength is proportional to the absorptivity of the substance (a constant at each wavelength), the path length (the distance the light travels through the sample) and the concentration of the absorbing substance. In these cases the Beer-Lambert Law holds:

A = a * b * c where a = the absorptivity of the substance b = path length c = concentration of the substance

When working in concentration units of molarity, the Beer-Lambert law is written as:

       A = * b * cε

where is the wavelength-dependent ε molar absorptivity coefficient with units of M-1 cm-1.

As, and b, both are constant, then it can be written that, A Ɛ c∝

If, absorbance (A) is plotted on Y-axis against concentration (c) on X-axis, a linear curve is obtained. It is called standard calibration curve. It follows the equation of a straight line, y = mx+c.

If the absorbance of an unknown sample is then measured, the concentration of the absorbing component can be determined from this graph.

0 2 4 6 8 10 120

2

4

6

8

10

12

f(x) = xR² = 1

Standard Calibration Curve

Concentration (µg/ml)

Abso

rban

ce

Paracetamol: Paracetamol is a widely used over-the-counter analgesic (pain reliever) and antipyretic (fever reducer). Paracetamol is classified as a mild analgesic.

Figure: Structure of Paracetamol

Indication:

Paracetamol is used to treat many conditions such as headache, muscle aches, arthritis, backache, toothaches, colds, and fevers. It relieves pain in mild arthritis but has no effect on the underlying inflammation and swelling of the joint.

Reagents:

Standard paracetamol powder Napa Tablet (Beximco company) Distilled water

Apparatus:

UV Spectrophotometer Test tube Pipette Measuring cylinder Volumetric flask Electronic balance Mortar and pestle

Filter paper

Procedure:

Preparation of stock solution:

1. 5 mg paracetamol powder were weighed by electronic balance2. This powder was taken in a 50 ml volumetric flask and was filled with distilled water upto the

mark.3. The flask was shaked well until the paracetamol powder was dissolved. This solution was the

stock solution.

Preparation of working standard:

1. 9 test tubes were taken, were marked serially from 1-9 and were kept in a test tube holder.2. Test tube marked 1 was taken and was added with 10 ml distilled water. No stock solution is

added in this test tube.3. Test tube marked 2 was taken and was added with 0.5 ml stock solution and 9.5 ml distilled

water.4. The dilution process was conducted for the rest of the test tubes.

Test Tube Number

Stock Solution (ml)

Distilled Water (ml)

Concentration (µg/ml)

1 0 10 02 0.5 9.5 53 1 9 104 1.5 8.5 155 2 8 206 2.5 7.5 257 3 7 308 3.5 6.5 359 4 6 40

Preparation of Sample Solution:

1. Take 5/10 tablets and measure the individual weight of each tablet by electronic balance2. Determine the average weight which is 565 mg3. Take the tablets and crush it in mortar and pestle

5 mg paracetamol is present in 5.65 mg of powder

4. Weigh 5.65 mg powder from the mortar and pestle by electronic balance and keep it in a 50 ml a volumetric flask

5. Add distilled water upto the mark6. Then the solution is filtered7. Take 1 ml of the filtrate in the test tube; add 9 ml distilled water.

Calibration of UV Spectrophotometer:

1. Turn on the UV spectrophotometer and wait for the calibration to be completed2. Fill 2/3rd of the cell with distilled water, set the wavelength at 249 nm and press the auto-zero

button

Determination of absorbance for the working standard and the sample solution:

1. Take test tube 1 and fill the cell with it2. Place the cell into the sample holder and measure the absorbance3. Same way, determine the absorbance of the working standard and the sample

Calculation:

Calculation of the experimental/calculated value:

From the standard curve, the following equation is obtained:

Concentration Absorbance0 05 0.19910 0.37815 0.57020 0.64925 0.89430 1.05935 1.31740 1.443

Sample(18.03) 0.651

Experimental concentration value, x = y-c/m

= (0.651-0.002)/0.036

=18.03

Calculation of the theoretical value:

50 ml stock solution contains 5 mg Paracetamol

1 ml stock solution contains 5/50 mg Paracetamol

So, concentration of the stock solution = 5mg/50 ml = 0.1 mg/ml = (0.1*1000) µg/ml = 100 µg/ml

Again,

5/10 ml diluted solution contains 100 µg Paracetamol

1 ml diluted solution contains 100/5 or 100/10 µg Paracetamol

= 20 or 10 µg/ml

So, Theoretical concentration value = 20 or 10 µg/ml

Determination of Potency:

Potency = Experimental value/Theoretical value *100

= (18.03/10)*100

=180.3%

Result: The potency of supplied paracetamol tablet is 180.3%

Comment: According to USP specification of potency for tablet should be 100±10. In our experiment, potency of paracetamol tablet was 180.3% which is not comply with specification. This study provides the knowledge of R2 value. R2 value of this study is 0.9948 which is near to 1. But drug didn’t pass the test.

Reason:

Drug didn’t pass the test due to experimental error. UV-spectrophotometer didn’t work properly. There may be some error to prepare the sample solution.

Precaution:

Apron must be worn. All equipments and instruments were handled properly. Standard and sample ingredients were weighed and handled properly.