Mass Spec Instrumentation (6) Flashcards
List the components of a mass spectrometer
Inlet systems, ion sources, mass analyzers, detectors, signal processors and vacuum systems
inlet system
Introduces small amounts of sample
ion sources
Convert sample to ions
mass analyzers
disperses ions by m/x ratio; analogous to monochromatic in photon spectroscopies
detectors
Converts ion beam into electrical signal
vacuum systems
Must maintain high vacuum 10e-4 to 10e-8 torr
What are the 3 ways to introduce samples into the ion source?
Batch inlet, direct probe, chromatographic inlet
What are the methods used to introduce gases in MS?
batch inlet; introduce through reservoir then leak the gas through a small aperture
chromatographic inlet
What are the methods used to introduce solids in MS?
direct probe inlet; insertion probe with sample held on end
What are the methods used to introduce liquids in MS?
batch inlet; syringe injection then heated
chromatographic inlet
GC chromatographic inlet
jet separator, packed capillary columns
What are the different types of LC-MS interfaces
direct liquid injection or thermospray or electrospray or CF-FAB
Direct injection used in?
microbore or capillary LC
Electrospray?
nebulize effluent by charging and extracting ions; liquid sample; high electric field; ions drawn into vacuum; analysis of high MW and nonvolatile analytes
Faraday cups advantages
Well shielded; can detect more than 10e-15 A currents
electron multipliers
most common; like a PMT without photocathode; each successive dynode held at higher voltage; can detect less than 10e-15 A currents
electro-optical detection (Array transducers)
like multichannel array detectors; arrays of metallic electrodes are used, each acting as an individual electron multiplier detector causing an electron cascade; optical coupling by phosphorescent screen converting electrons to light
LC chromatographic inlet
used for samples that are not volatile, not suited for gas phase; elution solvent must be eliminated
Faraday cups disadvantages
high impedence amplifier limits speed at which it can be scanned
Faraday cups principle
current passes through sensor to ground, but potential held at ground; charge of ions striking plate is neutralized by flow of electrons from ground through resistor; resulting potential drop is amplified
electron multipliers disadvantages
problems if exposed to atmospheric pressure because of reactive coatings
Which is more difficult: LC or GC?
LC because elution solvent must be eliminated
