17. Analytical Techniques Flashcards
The relative masses of some molecules which have fairly similar relative masses can be distinguished by…
High resolution mass spectrometry.
Which peak on a mass spectrum corresponds to the molecular ion?
The main peak furthest to the right of the mass spectrum.
A pair of atoms joined by a chemical bond is always…
Vibrating
Every bond has it own natural…
Frequency that is in the infra-red region of the electromagnetic spectrum.
What happens when we shine infra-red radiation through a sample?
The bonds in the sample can absorb the radiation that has the same frequency as the natural frequency of the bond. When the radiation emerges it will be missing the radiation that correspond to the bonds in the sample.
How does an infra-red spectrometer use this information?
The instrument plots a graph of the intensity of the radiation emerging from the sample (called transmittance) against the frequency of radiation (expressed as a wavenumber) (cm^-1).
An infra-red spectrum shows…
Peaks which represent particular bonds.
Where is the fingerprint region?
Below about 1500cm^-1
What can the fingerprint region be used to do?
We can use a computer to match the fingerprint region of a sample with those on a database of compounds.
Infra-red spectra can also be used to show up the presence of…
Impurities.
