Spectroscopy Flashcards
Define spectroscopy.
The production, measurement, and interpretation of spectra arising from the interaction of electromagnetic (EM) radiation with matter.
Describe how spectroscopic methods differ.
- The spectroscopy methods differ based on type of species, EM radiation-matter interaction, and the electromagnetic region.
- Spectroscopy methods may be qualitative or quantitative.
Define: electromagnetic radiation.
Radiation: the emission or transmission of electromagnetic energy in the form of waves or particles through space or through a material medium.
Electromagnetic radiation has wave and particle properties.
What are waves?
Disturbances in a particular physical medium or a field, resulting in a vibration or oscillation.
Electromagnetic waves consist of […]
Two waves oscillating perpendicular to one another; magnetic & electric fields
What is amplitude?
The height of the wave
What is wavelength?
The distance of one full cycle of the oscillation
What is frequency?
Defined as the number of cycles per second (sec^-1 or Hertz (Hz)).
What is the relationship between frequency and wavelength?
Frequency (v) = 𝑐/𝜆
Wavelength is inversely correlated to the frequency. (Frequency is directly proportional to energy).
What is the speed of light?
3 x 10^8 m/s
Discuss different wavelengths and frequencies of these waves.
- Red has longer wavelength and lower frequency (lower energy)
- Blue has shorter wavelength and higher frequency (higher energy)
Frequency and wavelength have an inverse relationship, meaning that as frequency increases, wavelength decreases.
Which parts of the electromagnetic spectrum are important in food analysis?
Food analyses use mostly UV to IR waves and radio wave ranges (e.g., Nuclear magnetic resonance)
Gamma rays are the most dangerous - higher frequency is generally more dangerous than lower frequency.
What is the relationship between frequency and wavelength?
The shorter the wavelength, the higher the frequency. Hence, frequency and wavelength are inversely proportional to each other.
Frequency and wavelength have an inverse relationship, meaning that as frequency increases, wavelength decreases.
Describe radio waves.
Long wavelength and low frequency/energy
Describe gamma rays.
Short wavelength and high frequency/energy
Electromagnetic (EM) radiation can either act as […].
a wave or a particle
What is a photon?
The elementary particle, or quantum, of light.
As a particle, electromagnetic radiation […]
transports energy
What about the particle property of electromagnetic radiation allows spectroscopy to work for identifying materials?
- Each atom has its own distinct set of energy levels
- Each element emits and absorbs different frequencies
Frequency is directly proportional to […]
Energy
Frequency is directly proportional to energy.
True or False?
True.
Frequency is inversely proportional to energy.
True or False?
False.
Frequency is inversely proportional to wavelength.
True or False?
True.
Frequency is directly proportional to wavelength.
True or False?
False.
What is Planck’s constant?
h = h= 6.62607 x 10^-34 J*s)
Describe the electromagnetic spectrum with regard to wavelength, frequency, and energy.
Describe how wavelengths relate to the type of spectroscopy.
Describe the energy states of matter.
- The energy content of matter is quantized.
- Atoms and molecules - normally in ground state; enter excited state upon gaining energy
Describe the energy levels of atoms and molecules.
- Atoms have different electronic states
- Molecules have different electronic, vibrational, and rotational states.
What is an electronic transition?
- The movement of the molecule is between two electronic states
- Electronic transitions take place when electrons int he molecule become excited from one energy level to another.
What is a rotational transition?
- The movement of the molecule is within the same vibrational state but between two different rotational energy states.
- Rotational transitions of molecules refer to the abrupt change in the angular momentum of that molecule.
What is a vibrational transition?
- The movement of the atom is within the same electronic state but between two different vibrational states.
- Vibrational transition of an atom refers to the movement from one vibrational energy level to another.
The absorption of radiation by an atom or molecule is […]
- The process in which energy from a photon or electromagnetic radiation is transferred to the absorbing species.
- Energy absorbed must be exactly equal to the energy needed to jump to the next energy state.
- The molecule is excited from the ground state to an exited electronic state with a simultaneous change in its vibrational or rotational energy levels.
What is emission?
- The reverse of the absorption process, occurring when energy from an atom or molecule is released in the form of a photon of radiation.
- Several relaxation processes through which an excited molecule may dissipate energy: vibriational; fluorescence.
What are the relaxation processes through which an excited molecule may dissipate energy?
- Vibrational relaxation: dissipation of the energy within on excited state; dissipated as heat to neighboring molecules; vibrational relaxation is a non-radiative transition.
- Fluorescence: dissipation of energy by emitting a photon; the emitted photon will be of lower energy and thus of longer wavelength.
What is vibrational relaxation?
Dissipation of the energy within one excited state; dissipated as heat to neighbouring molecules.
Vibrational energy is a non-radiative transition.
Vibrational energy is a non-radiative transition.
True or False?
True.
Vibrational energy is a radiative transition.
True or False?
False.
What is fluorescence?
- Dissipation of energy by emitting a photon.
- The emitted photon will be of lower energy and thus of longer wavelength.
Emission waves are longer than excitation waves.
True or False?
True.
Emitted photons will be of lower energy and thus of longer wavelength.
Emission waves are shorter than excitation waves.
True or False?
False.
They are longer.
Emitted photons will be of lower energy and thus of longer wavelength.
What is light scattering spectroscopy?
uses photons of light that are
scattered by the target medium
UV-VIS spectroscopy is used for the detection of:
Specific compounds
Fluorescence spectroscopy is used for the detection of: [5]
- Protein thermal stability
- Fat oxidation
- Fungal toxins
- ATP detection
- Food authentication/quality
Raman spectroscopy is used for the detection of:
- Chemicals
- Microorganisms, e.g., pesticides
- Fungal toxins
IR and near-IR spectroscopy is used in the detection of:
Almost anything
Emission spectrometry is used in the detection of [1]:
Metals
NMR is used in the detection of:
- Fat content of meats
- Anything with phosphorus
- Water content/distribution
MS is used in the detection of:
Almost anything
How do we determine the unknown concentration of a sample using UV-VIS spectroscopy?
Assuming a known compound:
A) Identify the maximum absorbance wavelength of the item of interest
B) Determine absorbance of a set of standards of the same compound at different concentrations
C) Determine equation of line
D) Solve for x (concentration)
What is HMF?
- HMF is generated by the decomposition of fructose in acid conditions. It occurs naturally in most honeys and increases rapidly with heat treatment of honey. Therefore, it can be used as an indicator of heating and storage time at elevated temperatures.
- Good quality honey has a lower amount of HMF.
Note this is qualitative analysis. For quantitative analysis a standard curve (prepare standards in honey) will be required.
Describe the analysis of pork adulteration in beef meatball using Fourier transform infrared spectroscopy.
The fatty acid composition of beef and pork is different, which is why this region is useful for deteriming whether adulteration is present.
Describe the use of surface-enhance Raman spectroscopy detection of melamine in milk.
Scattering spectroscopy
Describe the use of surface-enhanced Raman spectroscopy determination of pesticide penetration.
Scattering spectroscopy
What are the regions of visible wavelengths?
380-750 nm
What are the wavelength regions of ultraviolet ?
10 - 380 nm
What are the wavelength regions for infrared?
0.075 - 1000 um
What are the wavelength regions of microwaves?
0.1 - 100 cm
What are the wavelength regions of radio waves?
1 - 1000 m
What are the wavelength regions of x-rays?
0.1 - 10 nm
What are the wavelength regions of gamma waves?
0.01 - 1 A
Why do atoms lack vibrational and rotational states?
They lack bonds, so they do not have vibrational and rotational states.
Molecules have mutiple atoms.
Infrared spectroscopy never has electronic transitions.
True or False?
True.
IR spectroscopy utilizes vibrational levels within a single electronic state.
Infrared spectroscopy has electronic transitions.
True or False?
False.
IR spectroscopy utilizes vibrational levels within a single electronic state.
What is the difference between stokes and anti-stokes Raman scattering spectroscopy? What about Rayleigh scattering?
Anti-stokes: E > Eo
Stokes: E < Eo
Rayleigh: E = Eo
