Quantitative determination of paracetamol in a drug formulation
based on UV/Vis spectrophotometry
Tymo Zwakenberg S4326253; Esther Veenstra; September 28, 2022.
Aim and principle
UV/vis spectrophotometry is one of many methods to control the quality of pharmaceutical
products. Both the indentity and the purity of compounds can be checked. The UV/Vis
spectrophotometry method relies on the fact that absorption of light in the UV/Vis range through a
substance is characterized by the transitions of electrons of molecules, from the ground state to an
excited state. The specific wavelength that subsequently gets absorbed and measured is determined
by the difference between electron energy levels. It should also be taken into account that solvent
molecules can influence the height of a molecule's energy level by protonation and deprotonation.
This practical will test the effect of sample parameters on the obtained UV/Vis spectra, and a
quantitative determination of paracetamol in a drug formulation will be executed (Verpoorte, s.d.).
Materials and methods
All measurements will be executed and recorded by a manual Hitachi U-2900 spectrophotometer,
which is a double-beam spectrophotometer. In such an apparatus the sample signal is constantly
compared to the reference signal, ‘autozero’ must be performed before starting to measure. A
schematic overview of this principle can be seen in figure 1.
Figure 1: Schematic overview of a double-beam spectrophotometer (Verpoorte, s.d.).
The lab manual can be constructed for the overview of all the executed steps, no deviations were
inserted on that part. Additionally, the drug formulation that was provided contains 500 mg
paracetamol and 50mg caffeine, as stated by the TA. Ultimately, three different calibration curves
will be constructed in order to calculate the paracetamol content in the provided drug formulation
with a requirement of 90.0-110%. A list of materials, chemicals and calculation methods is provided.
Chemicals
- Drug formulation ( 699.2 mg), 35.0 mg was weighed of.
- Paracetamol stock solution (0.509 mg/ml)
- Caffeine stock solution (0.260 mg/ml)
- Control stock solution (0.256 mg/ml paracetamol & 0.104 mg/ml caffeine).
- 0.1 M NaOH.
- 0.1 M HCl.
- Ultra-pure water.
, Materials
- Volumetric flasks (100 – and 25 ml).
- Quartz cuvettes.
- Beakers.
- Ultrasonification bath.
- Syringe & filter.
- Gilson pipette.
- Glass pipette.
- Hitachi U-2900 spectrophotometer & printer.
- Mortar & pestle.
Calculation methods
- Calibration calculation: Transform obtained y = a*x + b into x = (y-b)/a. subsequently x
(unknown concentration) can be calculated.
- Deviation calculation: ((measured – reference)/reference) * 100%.
Results and discussion
Caffeine interference
Figure 2: Caffein absorbance in HCl (left) and NaOH (right) solutions.
Peaks of caffeine occurs at 271.5 nm with 0.491 Absorbance for HCl and at 272.5 nm with 0.508
Absorbance for NaOH.
based on UV/Vis spectrophotometry
Tymo Zwakenberg S4326253; Esther Veenstra; September 28, 2022.
Aim and principle
UV/vis spectrophotometry is one of many methods to control the quality of pharmaceutical
products. Both the indentity and the purity of compounds can be checked. The UV/Vis
spectrophotometry method relies on the fact that absorption of light in the UV/Vis range through a
substance is characterized by the transitions of electrons of molecules, from the ground state to an
excited state. The specific wavelength that subsequently gets absorbed and measured is determined
by the difference between electron energy levels. It should also be taken into account that solvent
molecules can influence the height of a molecule's energy level by protonation and deprotonation.
This practical will test the effect of sample parameters on the obtained UV/Vis spectra, and a
quantitative determination of paracetamol in a drug formulation will be executed (Verpoorte, s.d.).
Materials and methods
All measurements will be executed and recorded by a manual Hitachi U-2900 spectrophotometer,
which is a double-beam spectrophotometer. In such an apparatus the sample signal is constantly
compared to the reference signal, ‘autozero’ must be performed before starting to measure. A
schematic overview of this principle can be seen in figure 1.
Figure 1: Schematic overview of a double-beam spectrophotometer (Verpoorte, s.d.).
The lab manual can be constructed for the overview of all the executed steps, no deviations were
inserted on that part. Additionally, the drug formulation that was provided contains 500 mg
paracetamol and 50mg caffeine, as stated by the TA. Ultimately, three different calibration curves
will be constructed in order to calculate the paracetamol content in the provided drug formulation
with a requirement of 90.0-110%. A list of materials, chemicals and calculation methods is provided.
Chemicals
- Drug formulation ( 699.2 mg), 35.0 mg was weighed of.
- Paracetamol stock solution (0.509 mg/ml)
- Caffeine stock solution (0.260 mg/ml)
- Control stock solution (0.256 mg/ml paracetamol & 0.104 mg/ml caffeine).
- 0.1 M NaOH.
- 0.1 M HCl.
- Ultra-pure water.
, Materials
- Volumetric flasks (100 – and 25 ml).
- Quartz cuvettes.
- Beakers.
- Ultrasonification bath.
- Syringe & filter.
- Gilson pipette.
- Glass pipette.
- Hitachi U-2900 spectrophotometer & printer.
- Mortar & pestle.
Calculation methods
- Calibration calculation: Transform obtained y = a*x + b into x = (y-b)/a. subsequently x
(unknown concentration) can be calculated.
- Deviation calculation: ((measured – reference)/reference) * 100%.
Results and discussion
Caffeine interference
Figure 2: Caffein absorbance in HCl (left) and NaOH (right) solutions.
Peaks of caffeine occurs at 271.5 nm with 0.491 Absorbance for HCl and at 272.5 nm with 0.508
Absorbance for NaOH.
