Topic 7 - Modern Analytical Tech I Flashcards
What is mass spectrometry used for
identifying compounds
What are the 4 stages in mass spectrometry
ionisation
acceleration
deflection
detection
What happens during ionisation in mass spectrometry
- vaporised sample
- electrically heated metal coil gives off electrons which are attracted to the electron trap (positively charged plate)
- particles in sample are bombarded with a stream of electrons,
- energetic enough to knock electrons out of sample particles
- make positive ions.
What happens during acceleration in mass spectrometry
- positive ions are repelled away from very positive ionisation chamber
- pass through three slits, the final one of which is at 0 volts.
- All ions are accelerated into a finely focused beam
What happens during deflection in mass spectrometry
Different ions are deflected by the magnetic field by different amounts
- mass of the ion (lighter ions are deflected more)
- charge on the ion (ions with more positive charges are deflected more )
What happens during detection in mass spectrometry
- only one ion stream makes it right through the machine to the ion detector
- other ions collide with the walls - they will pick up electrons and be neutralised. - eventually = get removed from mass spectrometer by vacuum pump.
What is the need for a vacuum pump in mass spectrometry ?
ions produced in the ionisation chamber have a free run through the machine without hitting air molecules
what is the molecular ion peak
highest m/z
molecular mass
How can mass spectrometry be used to differentiate between similar molecules
different fragments produced
How does infrared spectroscopy work
IR radiation passed through sample
absorbed by covalent bonds
increases their vibrational energy
bonds in dif atoms absorb sif frequencies
What does infrared spectroscopy do
helps identify organic molecules
What do the peaks show in IR spectrum
where ionisation is being absorbed
