Analytical Spectroscopy Flashcards
What is the wave description of light?
Light is composed of an electric field and a magnetic field which oscillate at right angles to one another.
What is the wave equation?
C = V Lambda where: C = speed of light V = frequency Lambda = wavelength
What is the particle description of light?
Light is composed of discrete entities known as photons.
The energy of a photon is calculated by E = hv where:
E = energy
H = Plancks constant
V = frequency
Which equation is used to calculate the energy of light?
E = hc/lambda where: H = Plancks constant C = speed of light lambda = wavelength
describe the absorption of light by a molecule?
energy is transferred from a photon to a molecule causing it to move into a higher orbital/excited state.
Describe the emission of light energy from a molecule?
the molecule releases energy in the form of a photon and moves back to a lower orbital.
X-ray radiation causes which electron transitions?
Inner electron transitions; can lead to ionisation or photolysis (bond breaking).
Ultra violet radiation and visible light cause which electron transitions?
Outer (valence) electron transitions
i.e outer electrons move to a higher orbital.
The difference in what corresponds to the transitions between different energy states in atoms or molecules?
Difference in wavelength.
Infra-red radiation causes?
Vibration of bonds within molecules.
Microwave radiation causes?
Rotation of bonds within molecules.
Radiowave radiation causes?
Nuclear spin transitions.
Spectroscopy analysis can be either?
Quantitative or Qualitative
Qualitative analysis is described as?
Substances are IDENTIFIED based on the wavelength(s) that the absorb or emit.
Quantitative analysis is described as?
Concentrations of analytes are MEASURED.
Accuracy
The closeness of a measurement to the true value.
Precision
The closeness of a set of measurements to one another.
Selectivity
The degree to which the method responds to the selected analyte and not to the other matrix components. Ideally this is high.
Detection Limit
The lowest concentration we can detect with statistical certainty.
UV-Visible Spectrometry Steps:
- Shine light of the correct wavelength (corresponding to the change in energy in the analyte) through the solution.
- measure the proportion of light absorbed.
What equation is used to calculate the absorbance of an analyte?
A = log (Io/I) Where:
Io = incident radiation
I = transmitted radiation
N.B. absorbance has no units
what is the Beer Lambert Law?
The Beer Lambert law is the equation used to calculate the absorption of a substance and relates absorbance to concentration. A = e(epsilon) x C x l where: e= molar absorptivity C = concentration l = path length
Molar absorptivity relates to the probability of a particular electron transition occuring i.e?
Large molar absorptivity = intense colours
Small molar absorptivity = weak colours
What is a chromophore?
A chromophore is a particular functional group within a molecule that absorbs light, different chromophores have different absorption wavelengths and molar absorptivitys.
List some common chromphores.
- double or triple bonds and conjugated systems (benzene)
- Lone pairs of electrons on O, N or S
- Metal ion complexes.
