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Pharm303 LABS > Lab 1: Quality control of Aspirin and Paracetamol > Flashcards

Lab 1: Quality control of Aspirin and Paracetamol Flashcards

1
Q

What is quality control?

A

Common practice in the pharmaceutical industry before any new batch of raw material or final product will be used in manufacturing a dosage form such as a tablet

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2
Q

What is the aim of lab 1:

A

To confirm the identity and determine the purity of paracetamol and aspirin batches and ensure their compliance with BP specficiations

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3
Q

What is the chemical names of Aspirin?

A

Acetyl salicylic acid

2-acetoxybenzoic acid

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4
Q

Which part of aspirin is hydrolysed when reacting with NaOH?

A

The ester bond.

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5
Q

What are the main funtional groups used to identify aspirin in the IR spectrum?

A 
from highest wave number:
C=O
C=C
C-C
C-O
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6
Q

What is the functional group present in salicylic acid which was not present in acetylsalicylic acid?

A

The phenol group. This has been hydrolysed from the ester.

NB: the Carboxylic acid group also appears in the salicylic acid IR at around 1700 wavenumber

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7
Q

How many moles of NaOH is required to react with 1 mole of acetylsalicylic acid?

A

2

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8
Q

What is the equation of the hydrolysis of Acetylsalicylic acid?

A

Acetylsalicylic acid + 2NaOH -> sodium salicylate + CH2COO-Na+ + H2) + H2SO4 –> salicylic acid

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9
Q

Why was NaOH and sulfuric acid added to aspirin and boiled?

A

This was an identification test for Aspirin. The normal hydrolysis of acetylsalicylic acid will form a white precipitate, salicylic acid, or aspirin as the end product.

Formation of this white precipitate confirms the tablet is aspirin.

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10
Q

What causes the white precipitate of the aspirin identification test?

A

Carboxylic acid part of the aspirin reacting with the sulfuric acid.

the sulfuric acid sucks up the sodium, so there is no salt.

The white precipitate is the salicylic acid.

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11
Q

Why was ferric chloride, ethanol and icy water added to the precipitate?

A

Ethanol further broke up salicylic acid into phenol.

Ferric chloride forms an iron complex with the phenol

Icy water prevents the OH groups from ionising but enabled formation of VW bonds

The colourless solution should have turned purple further confirming the tablet was aspirin.

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12
Q

Why is 0.1M HCl solution used to titrate in the aspirin assay?

A

0.5M NaOH had a known amount of aspirin added to it. Indicator was also added.

By titrating this against the 0.1M HCl, we can see the volume of HCl required to neutralise the NaOH (Endpoint would be seen from the colour change of yellow to red using phenol red indicator.)

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13
Q

Why is the assay of Aspirin repeated with a blank substance?

A

This is also titrated with 0.1MHCl solution to determine the amount of HCl required to neutralise the NaOH.

By subtracting the test volume from the blank volume, we can determine the volume of NaOH reacting with the aspirin.

Via further calculations (n=m/M etc) we can determin the AMOUNT of NaOH reacting with aspirin.

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14
Q

How can we calculate the amount of aspirin present in the test sample (from the assay)?

A

You know the initial concentration of NaOH used was 0.5M
and the volume difference between the blank and test samples (in my group this is 7.12mL or 0.00712L
You can find the number of moles of NaOH and convert to mmol (this is 3.6mmol)

You know that 1 mol of aspirin reacts with 2 mol of NaOH which means 1.8mol of aspirin must have reacted.

The MW of aspirin is 180.15g/mol. now you can find out the mass of aspirin in mg

This comes to 324.27mg.
The percentage purity is out of a 500mg tablet, hence, 64.9%

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15
Q

What must the purity of aspirin in a sample be to pass the quality standards?

A

99.5-101%

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16
Q

What could account for the aspirin tablet failing the quality standards?

A

Most likely experimental error

17
Q

What is the functional group which gives a characteristic IR aborption of paracetamol?

A

The C=O from the amide group absorbs at around 1710 wavenumber

18
Q

What are the other functional groups of paracetamol abosrbing in the IR spectrum?

A

C-C: 1400
C-O: just under 1200
C=C: just under 1600

19
Q

How was absorbance used to calculate the concentration of paracetamol in a sample?

A

at 219nm, a 0.439 absorbance was obtained.

Then we use the beer lamber equation: A = εxbxc to determine the concentration, where the path length (b) is 1

20
Q

How is a dilution factor calculated?

A

e.g. 1mL of solution containing 0.05g/100mL is placed in a 100mL volumetric flask and water is added to make it up to volume.

The original solution has been diluted by a factor of 100 so should DECREASE or become smaller by a factor of 100, becoming 0.0005g/100mL

21
Q

What is %w/v?

A

the amount of g/100mL

22
Q

What is the hydrolysing agent used in step 3 of paracetamol analysis?

A

0.1M HCl

23
Q

What is the oxidising agent used in step 3 of the paracetamol analysis?

A

potassium dichromate

24
Q

What is the reaction of paracetamol with potassium dichromate?

A

Paracetamol in the presence of HCl and water hydrolyses to form 4-amino phenol.

4-amino phenol reacts with potassium dichromate and water to produce 1,4 benzoquinone

25
Q

What is the colour change observed with the oxidation of paracetamol with potassium dichromate?

A

Colourless (4-amino phenol) to brown (1,4-benzoquinone)

26
Q

What is the test of paracetamol contamination?

A

a test solution and a standard solution was prepared at the same time, each containing 0.2mL of 10g/l sodium nitroprusside and 10g/L anhydrous sodium carbonate.

The standard solution was at the limit of the allowed contamination, hence the test solution should not be more intense in colour than the standard for it to pass the test.

27
Q

How was the assay of paracetamol conducted?

A

a known amount of drug powder was mixed with 25mL of 0.1NaOH solution, 50mL of distrilled water and made up to 100mL.

This solution then underwent a 100x dilution factor and its absorbance was measured at 257nm

This was compared to a 500mg paracetamol tablet undergoing the same dilution factor with its absorance theoretically measured at 715nm (which is its specific absorance)

This gives us a percentage of 0.464/0.536x100 = 86.6%

28
Q

Did the assay of paracetamol comply with BP standards?

A

No the BP standards specified 99.5-101% and our assay showed 86.6%
Our failure is likely to be due to experimental error

29
Q

what is quality control?

A

a set of procedures intended to ensure that a manufactured product adheres to a defined set of quality criteria

30
Q

what are the three different types of quality that should be assessed in the pharmaceutical process?

A

quality of inputs
quality of partially completed products
quality of outputs

31
Q

What do quality of inputs evaluate?

A

quality of raw materials and supplies via control charts and acceptance tests

32
Q

what do quality of partially completed products evaluate?

A

the quality of production processes, via control charts

33
Q

what do quality of outputs evaluate?

A

the quatliy of products and services via control charts and acceptance tests

34
Q

What are the quality control tests?

A

Identity (MP, FTIR spectroscopy, other specific tests listed in BP e.g. white ppt of aspirin, absorbance of paracetamol)

Purity:
determine % purity using UV spectroscopy
determine the concentration of impurites

35
Q

What indicates impurity of Aspirin?

A

a broad melting point

36
Q

Why is the sodium nitroprusside added in the paracetamol contamination test?

A

It forms a blue complex with the 4amino phenol (hydrolysed product of paracetamol) the more phenol there is, the more intense the blue colour indicating a higher amount of contaminant

37
Q

Why is sodium bicarbonate added to the paracetamol contamination test?

A

It provides the basic environment required for nitroprusside to form the blue complex as an indicator for the presence of 4amino phenol

Pharm303 LABS (5 decks)

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