Mass Spectrometry Flashcards
define mass spectrometer
measures the masses of individual moleucles and atoms that have been converted into ions
- measure in daltons (da)
- use AMU
what is the general operation of spectrometry
- ionization of gaseous molecules and atoms to form ions
- ions are accelerated by electric field and separated by their mass-to-charge ratios (m/z)
- measurement of quantity of ions of each mass-to-charge ratios
define mass spectrum
-mass to charge can be plotted versus abundance to produce amss spectrum
- molecular ion is the ion that has the same elemental composition as the original molecule
- base peak is the highest peak with the highest abundance
what are teh 3 things a mass spectrometer consists of?
ion source, mass-selective analyze, and an ion detector
describe the general set-up for a spectrometer
- require high vacuum to ensure that analyte gas phase ions do not collide and charge transfer with neutral air molecules
- ions are transferred from ion source to analyzer that uses electric field
- ions are then detected
- use scan mode to detect all m/z ratios to SIM mode that selective certain ratios
define electron ionization, EI?
- most common
- energetic beam of electrons is generated from to filament, accelerated into ion source
- ions are created from the collision of gaseous molecules and the beam
- produce +, -, and neutral ions
- high energy electrons interact with any molecule not just ionization occurs, but bonds are broken and fragments are formed
- hard ionization (cause greater fragmentation)
define chemical ionization,CI?
- soft ionization (not breaking the molecule apart as much)
- uses excess of a reagent gas is introduced into ion source and becomes ionized
define electrospray ionization, ESI?
- sample is eluted from chromatography colum and is spray into the source chamber
- reduce size of molecules to have a highly charged analyte molecule
- used with polar compounds and biological molecular
- soft ionization technqiue
define MALDI-
- laser ionizaion method of vaporizing large moleculaes into a solid matrix
- ultraviolet laser pulse vaporizes the matrix to carry some of the molecules into the gas phase to be directed into spectrometer
define mass analyzers
to separate ions according to their mass-to-charge ratio
define magnetic sector
as ion leaves ion source, it is accelerated with kinetic energy through a magnetic field tubed to reach the detector
- ions can be selected by either adjeustin the magnetic field strength or by adjusting accelerating voltage
define quadrupole
- has 4 paralell rods
- a voltage comprising a constant voltage component and a radio frequency alternating voltage is applied
- only ions with the certain m/z will be able to pass through
- ions are selected by varying the voltage and frequency of the rods
define time fo flight, TOF?
- the simplest form of analyzers
- evacuated drift (flight) tube which is free of any magnetic and electric fields
- all ions exit the ion source with the same kinetic energy
- lighter ions will have a greater velocity compared to heavier ones making them reach the detector first
define ion detectors
to generate a current signal from the incident beam of ions
define electron multiplier detector
- most common
- electron multipliers use a process called secondary electron emission that has several dynodes maintained at increasing potentials
- ion hit surface of first dynaode and creates emission of electrons
- these elecrons are attracted to the next dynode, which is at a higher potential, and then just continues to reflect and double
