Midterm 2 Review Flashcards
What are ICP, ESI and MALDI used for?
Volatilization and ionization
What are EI and CI used for?
Ionization
What are quadrupole, TOF, fourier transform and ion traps used for?
Mass sorting
What are electron multipliers used for?
Detection
Isobaric Interference?
Results from equal mass isotopes of different elements present in sample solution
How to correct isobaric interference?
Use relative gas that forms product with similar mass to that of the unwanted isotope
Polyatomic Interference?
Combination of two or more isotopes from different elements in the same plasma
How to correct polyatomic interference?
Use hexapole collision cell to remove unwanted molecules
What are the 4 components of mass spec?
Sample inlet/volatilization
An ionization source
A mass analyzer
detector
ICP Torch
very very hot and makes ions to use in MS. Analyte must be separated before entering ICP. Laser adsorption to produce ions. Plasma detected through cooling cone. Extraction lens attracts positive ions from plasma. Ions enter collision cell (with H2 or He). Ions guided to mass spec
Interphase in MS?
Transport as many ions as possible to MS while excluding photons, neutrons and other unwanted particles that will produce unwanted signal.
Quadrupole advantages and disadvantages
compact, tough, cheap, high scan rate, BEST sensitivity
WORST resolution, slow, maximum ratio
Time of flight advantages and disadvantages
Simple, can combine with many ion sources, unlimited mass range, FAST
low sensitivity and resolution
Double focusing advantages and disadvantages
BEST resolution, double focuses
Huge and expensive, requires extensive knowledge to operate
3 main uses of MS
- Analysis of pure compound (give molecular mass, dormula, isotopic ratio, fragmentation patterns
- Mixture analysis (requires separation using GC-MS, LC-MS, CE-MS)
- Quantification (requires internal standards and cal curve)
Applications for molecular MS
pharmaceutical analysis, forensics, food safety
Electron impact advantages and disadvantages
Cheap, touch, reproducible
rough on molecule, molecular ions do not survive, entire class of compounds does not work
Exact Mass?
Calculated
Accurate mass?
Actual measured m/z
Chemical ionization?
a gaseous reagent is introduced into ionization region. Ionized carrier gas with EI and collides gas with analyte
CI advantages and disadvantages
nice and gentle, molecular ion will survive, cheap
Molecule must be volatile, not reproducible, low polarity requires
Electrospray Ionization (ESI)
used for large molecules where fragmentation is avoided.
Dispersal of fine spray charges droplets followed by solvent evaporation and ion ejection. Sample is injected into high voltage capillary and comes out as a highly charges mist. Solvent evaporated with N2. Molecular ions then repel each other and charged analyte is ejected into mass analyzer.
Matrix Assisted Laser Desorption ionization (MALDI)
Analyte is mixed in matrix solvent and applied to metal plate. A laser light hits causing energy absorption. The analyte is ionized and ejected into gas phase and is then accelerated into chosen MS.
Very expensive but has HIGHEST m/z ratio
Fourier transform ion-cyclotron MS (FTIC)
Used a magnetic field to trap ions into an orbit (centripetal force).
Multiple reaction monitoring (MRM) vs Selected “” (SRM) vs product ion scan (PIS)
MRM/SRM monitors each precursor ion/product ion transition at a time.
SRM is monitoring only a single fixed mass window
MRM scans rapidly over multiple mass windows and thus acquires traces of multiple fragment ion masses
PIS used for qualitative applications to obtain structural information.
Q1 is set to allow only the transmission of one m/z. The parent ion collides with Argon gas in Q2 to create fragment or product ions. Product ions are scanned through Q3
All allow relative and absolute quantification of proteins, peptides and metabolites.
