Topic 7 - Modern Analytical Techniques 1 Flashcards
What can mass spectrometry be used to identify?
- number of isotopes within a sample
- relative abundance of each isotope
What are the (5) stages in a mass spectrometer?
- vapourisation
- ionisation (by electron bombardment)
- acceleration (from electric field)
- deflection (from electromagnet -determines mass)
- detection (by charged plate -generated potential difference proportional to charge of ion)
How are atoms ionised in a mass spectrometer?
- electrons are fired by an electron gun at the atoms
- causes atoms to loose e- (becoming positively charged)
How are ions accelerated in a mass spectrometer?
by an electric field
How are ions deflected in a mass spectrometer?
by a magnetic field
What is a molecule’s fragmentation caused by?
unstable positive ion after electron bombardment
What are the 2 parts to a fragmentation?
- positive ions
- free radical
What is the molecular ion (M+) peak equal to?
molecular mass of unfragmented compound
What does a mass spectra show us?
- molecular mass of a compound
- information of compound’s structure (using its unique fragmentation pattern)
What is infra-red spectroscopy?
instrumental analysis technique used to identify types of bonds in a molecule
-allows us to identify functional groups
What does a bond require to become excited when using infra-red spectroscopy?
a specific frequency in the infra-red spectrum
-this energy (frequency/wave number) is absorbed
What is the relationship between wavenumber and frequency?
directly proportional
What does a wavelength absorbed by a bond depend on?
- bond length
- bond strength
- mass of each atom either side of the bond
What happens when a bond absorbs energy?
the bond does any of three things:
- stretches (asymmetric or symmetric)
- bend (like a pendulum)
- vibrate
What are the two types of bond stretching?
- asymmetric (alternatively stretching and contracting)
- symmetric (simultaneously stretching and contracting)
