IA CH 20 Mass Spectrometry

Define Hard Ionization
Sources that imparts enough energy to an analyte molecule to leave them in a highly exited energy state. Relaxation involves rupture of bonds producing fragment
Define soft ionization
source imparts lesser extent of energy resulting fewer fragments
Define molecular ion peak
tells molecular weight
Define base peak
represent most stable ion, fix to 100%
Define fragment peaks
how the molecule breaks up
Draw the mass spec system
do on separate sheet of paper
Define Inlet
How the sample is introduced
What are the two types of inlets for a mass spec?

1) Direct probe

2) connection to separation system

Define Direct probe
introduction of sample manually
Scenarios for direct probe use
-want sample directly in ms
-starting with pure sample
-have minimal sample
Define connection to a separation system
up front separation using
GC- organics
ICP- inorganics
HPLC- anything molecular
What are the two types of ion sources?
1) gas phase source
2) desorption source
What are the two gas phase sources in MS

1) Electron impact

2) Chemical ionization

Describe electron impact
-bombard molecule with ton of electrons
-hi detection limit, only 1 per million ionzied
Draw the Electron impact system and the chemical reaction involve
Separate sheet of paper
Describe chemical ionization
Gaseous atoms of the sample are ionized by collision w/ ions produced by electron bombardment of excess reagent gas
Write out the chemical ionzization reactions(general, proton transfer and hydride transfer).
Refer to book and notes
Describe desorption source
-used for non volatile and thermo stable molecules
-used for high molecular weight samples
Describe how MALDI works
1)Evaporate sample on MALDI matrix
2)Place sample matrix in vacuum
3)Hit matrix with laser, matrix absobs photon and transfers energy to sample
4) Ion plume goes to mass azalyzer
What are the three types of mass analyzers
1) quadrapole
2) Time of flight
3) ion trap
Draw a quadrapole
Refer to book and notes
Explain a quadrapole
Altering the RF to DC ratio in the four parallel electrode you can alter the oscillation patterns of the ions and select for a narrow range of m/z
What are the advantages and disadvantages of the quadrapole
advantage: fast scan rate, low detection limit
disadvantage m/z limit of 3000-4000
Explain Time of flight
A spatially tight bunched group of ions produced by MALDI is accelerated in a drift tube where separation occurs based on velocity. (.5mv^2=KE)
What are disadvantages of Time of flight
-Molecules are constantly stream towards detector
-low sensitivity
-requires good electronics
Draw Ion Trap
Refer to book and notes
Explain how ion trap works
Ions with specific m/z are stabilized between two ring electrodes before the RF is change to kick out ions
Define mass selective ejection
sequentially ejects ions in order of increasing mass by increasing RF-voltage to ring electrode
List the 11 applications for mass spec:
1)Elucidation of the structure of organic and biomolecules
2)determination of the mw of biomolecules
3)ID of components in TLC
4)Determination of aa squence in polypeptide
5)Detection and ID of species separated by chromatography
6)ID of drugs and metabolites in blood urine and saliva
7)Monitoring gases in surgery patients
8)dating archaeological specimens
9)analysis of aerosols
10)determination of pesticide residues in food
11)monitoring volatile organics in water supplies