Mass Spectroscopy Flashcards
what is spectroscopy?
spectroscopy is a non-destructive analysis technique where electromagnetic radiation is passed through a substance to analyze it
what is electromagnetic radiation?
EMR is energy that travels in wave motion and can pass through a vacuum. It includes gamma rays, X-rays, UV light, visible light, infrared, microwaves, and radio waves.
what is the relationship between wavelength, frequency and velocity of EMR?
Velocity of a wave is the product of its wavelength and frequency : . For EMR, (speed of light).
what are the types of spectrums in spectroscopy?
- Emission Spectrum: Energy emitted by excited molecules analyzed by a spectrometer.
- Absorption Spectrum: Energy absorbed, reflected, and transmitted analyzed by a spectrometer.
what are the types of spectrums in spectroscopy?
- Emission Spectrum: Energy emitted by excited molecules analyzed by a spectrometer.
- Absorption Spectrum: Energy absorbed, reflected, and transmitted analyzed by a spectrometer.
what is ultraviolet spectroscopy?
It involves the absorption of UV light by molecules, causing electron transitions between bonding and anti-bonding orbitals.
what are chromophores?
Chromophores are structural features of a compound that absorb UV energy at specific wavelengths, helping in identification.
state Beer-Lambert’s law
The extent of UV light absorption is proportional to the concentration and path length of the sample: , where is the molar absorptivity constant.
what is conjugation in spectroscopy?
Conjugation refers to delocalization in alternating single and double bonds, reducing the energy needed for transitions, leading to absorption in the visible spectrum.
what are the major uses ofUV spectroscopy
- Detecting chromophores.
- Measuring concentrations of substances (e.g., glucose in blood).
- Analyzing pollutants or substances in water.
what are the two types of molecular variations in IR spectroscopy?
- Stretching vibrations: Rhythmic changes in bond lengths.
- Bending vibrations: Changes in bond angles.
what is the significance of the fingerprint region in IR spectroscopy?
the fingerprint region is unique to each compound, aiding in its identifiation
what is the significance of the fingerprint region in IR spectroscopy?
the fingerprint region is unique to each compound, aiding in its identifiation
what materials are used in IR sample preparation and why?
NaCl or KBr is used since they do not absorb IR radiation, ensuring 100% transmission through the sample.
list some uses of IR spectroscopy
- Identifying functional groups.
- Forensic analysis.
- Monitoring atmospheric pollutants.
- Breathalyzer tests.
how do you prepare a solid sample
- Add a few drops of the oily liquid (nujol) and make into a mull.
- The mull is then placed between a pair of discs made of KBr or NaCl.
- The discs are then placed in the IR spectrometer and absorbance is measured
how to prepare a liquid sample?
Place a few drops of the liquid between a pair of discs made from NaCl or KBr
how to prepare a gas sample?
Place the gas in a cell 10cm wide. The walls of the cell are made from NaCl or KBr
describe the bond spotting region
(4000 cm-1- 1200 cm-1)- in this region, there are few peaks and isused to identify the bonds and the functional group in a compound.
describe the bond spotting region
(4000 cm-1- 1200 cm-1)- in this region, there are few peaks and isused to identify the bonds and the functional group in a compound.
condition for IR to be absorbed
the molecule must possess a dipole or the vibration mustcause a change in the dipole moment.Symmetrical diatomic molecules will not absorb IR radiation.
role of a complexing agent
If a substance does not absorb light in the UV visible part of the spectrum, it can be made to absorb by adding a complexing agent.
The complexing agent reacts with the substance to produce a particle which absorbs (ex. Add potassium thiocyanate to make Fe2+ absorb).
uses of a complexing agent
To detect the presence of chromophores in the substance
To obtain the concentrations of dilute solutions by measuring absorbance
what is a calibation curve?
A calibration curve is a plot of absorbance against concentration for a sample. This curve is veryuseful to determine the concentration of a solution by measuring its absorbance.
assumptions of Beer Lambert’s Law
- The light passing through the substance must be monochromatic ie. UV light of a singlewavelength.
- The absorption process must take place in a volume over a uniform area.
- The substance which is absorbing must behave independent of the solvent used.
- This law is generally obeyed by dilute solutions.
Beer Lambert equation
A= molar absorptivity constant x concentration x wavelength
transitions from ultraviolet light
π → π#
n → π#
n → σ#
orbitals formed during overlapping of two orbitals
bonding molecular orbital
anti-bonding molecular orbital
equation for energy using Planck’s constant
𝐸 = ℎ𝑓
𝐸 = ℎ𝑐 / λ
