Interview Questions on UV-Visible and IR spectroscopy

What is IR spectroscopy?

IR spectroscopy studies the interactions between Infrared radiation and Matter.

It is Electromagnetic radiation.

The range of the infrared region is 12800 ~ 10 cm⁻¹ and can be divided into

• Near-infrared region (12800 ~ 4000 cm⁻¹),
• Mid-infrared region (4000 ~ 400 cm⁻¹) and
• Far-infrared region (50 ~ 1000 cm⁻¹

What is the full form of the FTIR?

Fourier transform infrared

What is FTIR spectroscopy?

The FTIR spectrophotometer is the Michelson Interferometer and it contains

• IR source
• Beam splitter
• Fixed mirror
• Rotating mirror
• Sample compartment and
• Detector

What is the range of the Near-infrared region, Mid-infrared region and Far-infrared region?

• Near-infrared region (12800 ~ 4000 cm⁻¹), 
• Mid-infrared region (4000 ~ 400 cm⁻¹) and 
• Far-infrared region (50 ~ 1000 cm⁻¹

How does infrared radiation interact with the sample?

• Due to internal electronic rearrangement, atoms in the molecule don’t remain fixed at their positions but continuously vibrate at specific frequencies and produce IR radiation
• That vibrational frequency falls in the IR range
• When IR radiation passes through the sample it triggers the vibration of specific molecular bonds  and  specific frequencies of the IR radiation are absorbed
• The absorbed specific frequencies are “missing” from transmitted light

What are the different types of vibration in the molecules?

Symmetric stretching, Antisymmetric stretching and  Bending-like vibrations. Other vibrations are: Rocking, twisting and wagging

What is the Michelson Interferometer?

The Michelson Interferometer contains:

• IR source
• Beam splitter
• Fixed mirror
• Rotating mirror
• Sample compartment and
• Detector

How is the IR test (of a given sample) performed?

• Sample is prepared in KBr or solvent as mentioned in the method of analysis
• First Blank IR (without sample or standard) is performed for the background noise corrections
• Then after standard IR is performed
• Then sample IR is performed &
• Finally, the sample IR spectrum is compared with the standard IR spectrum

What is the procedure to identify a given unknown sample using FTIR?

• Sample is prepared in KBr or solvent as mentioned in the method of analysis
• First Blank IR (without sample or standard) is performed for the background noise corrections
• Then after standard IR is performed
• Then sample IR is performed &
• Finally, the sample IR spectrum is compared with the standard IR spectrum

What is the fingerprint region?

Just like the thumb impression/print of two different persons cannot be the same, similarly the IR spectrum of two different samples cannot be the same.

What are the different applications of FTIR?

It is used for both qualitative and qualitative analysis e.g. functional group identification, structure identification, content tests etc. in the

• Pharmaceutical industries
• Forensic Labs
• Polymer industries
• Foods Industries

Why KBr is used for palate preparation in FTIR?

It gives a transparent palate and secondly, it is readily available in pure for. That is why KBr is used in FTIR.

What is used for the calibration of FTIR?

A polystyrene film reference standard (with valid COA) is used for the calibration of FTIR. The thickness of the Polystyrene film should  be 38µ (micron) or 0.038mm

Why polystyrene film is used for the calibration of FTIR?

The polystyrene coating prevents degradation of the KBr window from moisture content. Secondly is is stable and gives characteristics peaks in FTIR. That is why polystyrene film is used for calibration of FTIR.

What are the peaks of the polystyrene film?

The polystyrene film gives strong FTIR peaks around 2847 – 3068, 1658, 1498, 751, 540cm^-1

What are the differences between KBr mode and ATR mode in FTIR?

In KBr mode pallet is prepped to perform the FTIR whereas in ATR mode direct sample is taken to perform the FTIR.

What are the advantages of FTIR?

• Fast analysis
• Low analysis cost.
• No need of of special skill

What are the weaknesses of the FTIR?

It is more suitable for qualitative analysis (like identification test and functional groups identification) and less suitable for quantitative test (like assay and content test)

Why is water not used in the FTIR?

Water can destroy the KBr window and secondly, water has strong IR peak due to -OH group. That is why water is not used in the FTIR.

What is the working range of the FTIR?

4000 to 600 cm^-1

At what wavenumber carbonyl group give peak in FTIR?

1760 to 1665cm^-1

At what wavenumber hydroxyl group (-OH) gives peak in FTIR?

3500 to 3200 cm^-1

At what wavenumber hydroxyl group (-NH₂) gives peak in FTIR?

3200 to 3600 cm^-1

Check out this link to learn answers related to UV detector question:s

• What is the UV spectroscopy?
• Which type of solvents are used for sample analysis by UV spectroscopy?
• What is E1% sol?
• What is the UV range?
• What is the Beer Lambert LAW?
• What is the visible range?
• Which type of samples are analyzed by UV spectroscopy?
• What is chromophores?
• What is Redshift?
• What is the blue shift?
• What is the effect of solvents on UV Maxima?
• What are the different applications of UV spectroscopy?
• What are the limitations of UV spectroscopy?
• What is the difference between IR spectroscopy and UV spectroscopy?
• What is UV spectroscopy?
• How IR spectrum can be obtained?

Abbreviations:

• UV: Ultraviolet spectroscopy
• FTIR: Fourier transform spectroscopy