18 Questions
What is the typical transmittance range for a C triple bond (alkyne) signal in IR spectrum?
80% or more
What is the function of the beam splitter in a Michelson interferometer?
To split the light and direct it towards fixed and movable mirrors
What is the main advantage of FT-IR over dispersive IR spectrometer?
Simultaneous measurement of all wavelengths
What is the purpose of the He-Ne laser beam in a Michelson interferometer?
To measure the distance of the moving mirror
What is the first step in getting a sample's FT-IR spectrum?
Without sample, obtain raw signal called ‘interferogram’
What is the main advantage of FT-IR in terms of signal to noise ratio?
It has a higher signal to noise ratio
What is the primary objective of dividing the FT spectrum of a sample by the reference spectrum?
To obtain the transmission spectrum
What is the main advantage of FT-IR spectroscopy over dispersive IR spectrometers?
Ability to analyze liquids and solids
What is the range of protein concentration that can be measured using FT-IR spectroscopy?
0.1μg/μl to >100 μg/μl
What is the primary limitation of FT-IR spectroscopy in analyzing protein samples?
Water interference with the amide I band
What is the primary application of FT-IR spectroscopy in protein characterization?
Characterizing the secondary structure of proteins
What is the primary advantage of FT-IR spectroscopy in terms of sample preparation?
Requires minimal sample preparation
What principle of IR spectroscopy allows for the identification of functional groups in a sample?
Energy absorption at specific wavelengths
What frequency range is typically measured in wave numbers in FTIR?
4000 – 600 cm$^{-1}$
What does FTIR rely on to generate spectra?
Absorption in the infra-red region
What is a key advantage of FTIR over dispersive IR spectrometer?
Faster data acquisition
How can a sample's FT-IR spectrum be obtained?
Recording the sample's response to infra-red radiation
What specific absorption corresponds to in FTIR spectroscopy?
Type of bonds present in the molecule
Study Notes
Infrared (IR) Spectroscopy
- IR spectrum measures absorption of IR radiation by molecules
- Atoms are in continuous motion, and bonds are rotating, resulting in different types of motions occurring in bonded atoms
- Each motion occurs at a specific energy, which is utilized to generate IR spectrum
IR Spectrum Measurement
- IR source: Mid IR (Nernst glower, Globar source), Near IR (Tungsten halogen), Far IR (High pressure Mercury vapour lamp)
- Traditional dispersive IR spectrometer: IR source, diffraction grating, light is directed towards diffraction grating, and each beam is mechanically directed towards the sample
- FT-IR spectrometer: Michelson interferometer, beam splitter, fixed and movable mirrors, and simultaneous measurement of all wavelengths
Advantages of FT-IR
- Improved signal to noise ratio
- Fast
- Accurate wavenumber
FT-IR Spectrum Application
- Identify and verify samples
- Characterize new materials
- Useful in manufacturing, chemical synthesis, R&D, and pharma sector
- Analyze chemical reactions, including those with functional groups
- Protein characterization, including secondary structure, and ligand screening
FT-IR Spectrum of Proteins
- Amide I: C=O stretching, characteristic of secondary structure
- Amide II: N-H bending and C-N stretching
- Shape and location of Amide I are characteristic of secondary structure
Protein Characterization using FT-IR
- Application 1: Protein secondary structure characterization, particularly sensitive to β sheets
- Application 2: Proteins structural transitions, stability
- Application 3: Protein concentration estimation, accurate and precise, requires pre-calibration
- Application 4: Identification and characterization of impurities, distinct peaks than proteins
Additional Benefits of FT-IR
- Analyze sample as it is
- Results within minutes
- Not limited by buffer components
- Liquids or solids can be analyzed, even opaque
Limitations of FT-IR
- Water: Temperature sensitive, strong signal masks amide I band
- Low concentration: Low signal
- Atmospheric interferences: Water vapour, CO2, require high-end IR spectrometer
Explore the various applications of FTIR (Fourier Transform Infrared) spectroscopy such as identifying, verifying samples, characterizing new materials, and addressing questions about chemical reactions. Learn how FTIR spectra can be used in manufacturing, chemical synthesis, R&D, pharmaceuticals, catalysis, protein characterization, ligand screening, and more.
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