8102172
Description
Mind Map by Charlotte Ansell, updated more than 1 year ago
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Created by Charlotte Ansell
over 7 years ago
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Spectroscopic
techniques
- Mass Spectrometry
- Stages
- 1) Vaporisation of sample
- 2) Ionisation
- Molecules are
bombarded by an
electron gun
- form +1 ions
- Molecules are
bombarded by an
electron gun
- 3) Acceleration
- using an electric field
- using an electric field
- 4)
Separation/deflection
- The lower the mass to
charge ratio the more it will
be deflected
- The lower the mass to
charge ratio the more it will
be deflected
- 5) Detection
- using computer methods
- using computer methods
- 1) Vaporisation of sample
- Time of Flight Mass Spectrometry (TOF-MS)
- Used to separate and to measure
the relative masses of the ions
produced under high-vacuum
conditions
- Used to separate and to measure
the relative masses of the ions
produced under high-vacuum
conditions
- History
- 1918 by Francis W Aston, a
student of J J Thompson (the
man who discovered the
electron
- Aston used the instrument to show that there were
different forms of the same element. We now call
these isotopes.
- 1918 by Francis W Aston, a
student of J J Thompson (the
man who discovered the
electron
- Uses
- Initially used to
show the identity
of a isotopes
- Now used to calculate
molecular masses and
characterise new compounds
- Initially used to
show the identity
of a isotopes
- A spectrometer
- Stages
- Infra-Red Spectroscopy
- The Infra-red Spectrophotometer
- A beam of Infra-red
radiation is passed
through the sample
- A similar beam is passed through
the reference cell
- The frequency of the
radiation is varied
- The amount of radiation absorbed by
a substance is compared with the
radiation
- The results are stored
and plotted
- A beam of Infra-red
radiation is passed
through the sample
- Key points
- In IR spectroscopy molecules
absorb frequencies
corresponding to their
functional group. These
absorptions are resonant
frequencies i.e the frequency
of the absorbed radiation
matched the vibrational
frequency.
- Energy quoted in
wavenumbers. Unit= reciprocal
centimetres cm-1
- The amount of vibration
depends on...
- 1) Bond strength (and bond length)
- 2) the mass of each atom
- 1) Bond strength (and bond length)
- For a molecule to absorb IR,
vibration with in the
molecule (stretching or
bending) must cause a net
change in the dipole
moment)
- Peak position depends on 1)
Bond strength 2) masses of
the atoms joined by the
bond
- Strong bonds and light atoms absorb at lower
wavenumbers. Weak bonds and heavy atoms absorb
at high wavenumbers.
- In IR spectroscopy molecules
absorb frequencies
corresponding to their
functional group. These
absorptions are resonant
frequencies i.e the frequency
of the absorbed radiation
matched the vibrational
frequency.
- The Fingerprint region
- Called the fingerprint region
because it is specific to each one
- The low wave spectrum of the graph
(usually between 600 cm-1 and 1400 cm-1)
is known as the fingerprint region
- This region is characteristics
of each individual compound,
and can be compared to a
known database)
- Called the fingerprint region
because it is specific to each one
- The Infra-red Spectrophotometer
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