IR Spectroscopy's Most Common Interview Questions with Answers for the Quality Control Department of a Pharmaceutical Company.
IR spectroscopy interview questions for freshers
1. What is IR spectroscopy?
IR spectroscopy is the study of the interaction between infrared radiation and matter by absorption, emission, or reflection.
2. What is the general chapter for IR spectroscopy?
USP general chapter <854> (Mid-IR)
3. What is the principle of IR spectroscopy?
After IR light passes through the analyte, there is a change in the vibration and rotational movements of atoms present in the sample. When the frequency of the IR radiation equals the frequency of vibration, the molecule absorbs IR radiation, and a peak is observed.
4. How many regions are there in IR spectroscopy?
There are three regions of IR spectroscopy:
- Far-IR: 400 to 10 cm⁻¹
- Mid-IR: 4000 to 400 cm⁻¹
- Near-IR: 12500 to 4000 cm⁻¹
Generally, mid-IR is used for analysis in the pharmaceutical industry.
5. How many regions are there in mid-IR spectroscopy?
There are two regions in mid-IR spectroscopy:
- Fingerprint region
- Functional group region
6. What is the scanning range of IR?
The scanning range of IR is 400 cm⁻¹ to 4000 cm⁻¹.
7. What is the scanning range of the fingerprint region?
The scanning range of the fingerprint region is 1500 cm⁻¹ to 400 cm⁻¹.
8. What is the scanning range of the functional group region?
The scanning range of the functional group region is 1500 cm⁻¹ to 4000 cm⁻¹.
9. What is the measuring unit of the IR spectrum?
The measuring unit is centimeter (cm-1).
10. What is wavenumber?
Wave number=1/wavelength (cm)
11. Which test do we perform in IR spectroscopy?
An identification test is performed. In this, the IR absorption spectrum of the sample should be consistent with that of the IR spectrum of the standard.
12. What do we use for IR calibration?
We use polystyrene film for calibration.
13. Why is polystyrene film used for IR calibration?
Polystyrene film is made of the polymer of styrene.
- Polystyrene is a stable material at any temperature
- It has high durability.
- It exhibits well-defined and easily recognizable absorption peaks in the mid-IR region.
14. Why is KBr used in IR spectroscopy?
It does not absorb IR radiation in this range.
- The dipole moment of KBr is zero.
- KBr has a transmittance of 100% in the range of 4000 cm⁻¹ to 400 ⁻¹..
- It does not react with the sample due to its neutral properties
- It has high mechanical strength.
15. In what ratio are KBr and the sample used for analysis in IR spectroscopy?
300 mg of KBr + 1 mg of sample is mixed.
16. How many types of molecular vibrations in IR spectroscopy?
There are two types of molecular vibrations in IR spectroscopy:
A. Stretching vibration
B. Bending vibration
Stretching vibration is further divided into two types:
i. Symmetrical
ii. Asymmetrical
Bending vibration is further divided into two types.
i. In-plane
ii. Out-of-plane
In-plane is again divided into two types: Scissoring and Rocking
Out-plane is further divided into two types: Wagging and Twisting
19. What is the difference between UV and IR spectroscopy?
UV, or visible, absorption spectroscopy typically measures absorption as a function of wavelength in nm. While IR spectroscopy typically measures transmittance as a function of wave number in cm⁻¹..
20. What are stretching and bending vibrations?
In a stretching vibration, vibration or oscillation along the line of the bond causes a change in bond length.
In bending vibration, the bond angle is altered.
21. What are the factors affecting the frequency of IR absorption?
- Relative mass of the atom.
- The force constant of the bond.
- Geometry of the atom.
22. What are the instrumentation components of IR?
i. IR radiation sources
ii. Wavelength selector (monochromator)
iii. Sample Holder or Cell
iv. Detector
v. Recorder
23. Why is water not used in IR spectroscopy?
- Water has two strong infrared absorption peaks.
- In IR, alkali halide disks are frequently dissolved by water, a strongly polar solvent.
24. Why are IR peaks inverted?
In infrared spectra, the absorption peaks point downward because the vertical axis is the percentage transmittance of the radiation through an organic molecule interacting with infrared radiation.
25. What are the applications of IR spectroscopy?
- Identification of functional groups and structure of organic compounds.
- Study of covalent bonds in molecules.
- Studying the progress of reactions.
- Detection of impurities in a compound.
- The ratio of cis-trans isomers in a mixture of compounds.
- The shape and symmetry of an inorganic molecule.
- Study the percentage of water in a sample.
26. How many types of lamps are used in IR spectroscopy?
- Tungsten Halogen Lamp: for the Near IR Region
- Nernst Glower Lamp or Globar Lamp: for the Mid-IR Region
- High-Pressure Mercury Lamp: for the Far IR Region
28. What is the difference between IR and FTIR?
IR stands for
|
Dispersive IR |
FTIR |
|
IR stands for
Infra-Red. |
FTIR stands for
Fourier Transform Infra-red. |
|
It has a single or
double beam. |
It has an
interferometer. |
|
Slow and imprecise
method. |
Fast and precise
method. |
|
It has one fixed mirror,
which produces only constructive interference. |
It has one fixed mirror
and one moving mirror, which can produce both constructive and destructive
interference. |
29. Which detector is used in IR spectroscopy?
The pyroelectric detector is the most commonly used detector among all IR detectors.
30. What are the two types of IR spectroscopy?
The two types of infrared spectrometers are dispersive spectrometers and Fourier transform infrared spectrometers.
31. What is transmittance?
Transmittance is defined as the light passing through an object that is not reflected or not absorbed. It is the fraction of incident light that is transmitted. The amount of light that successfully passes through the substance and comes out the other side.
32. What is absorbance?
Absorbance is the flip side of transmittance and states how much of the light is absorbed by the sample.
33. How is transmittance different than absorbance?
Transmittance is inversely proportional to absorbance. When absorbance is 100%, then transmittance is 0%. It means when absorbance increases, then transmittance decreases.
17. What is scissoring and rocking vibration?
In the scissoring type of vibration, two atoms move in opposite directions and get close to each other. In rocking, two atoms move in the same direction so the bond angle is maintained.
18. What are wagging and twisting vibrations?
In the wagging type, two atoms oscillate up and down on the plane, down the plane side of the central atom during this process. In twisting, one atom travels in the plane's center, while the other moves in the opposite direction. One plane is above the plane, and the other plane is below the plane.
27. What is the thickness of polystyrene film?
The thickness of the polystyrene film is 38 microns.
