Mass Spec 3&4 (Flo-2) Flashcards
How does a photomultipler (PM) detect ions?
- Ions are attracted to end MSR and hit dyode.
- ions striking releases electrons
- electrons attracted to phosphorus screen and strike again and release photons
- these are converted to electrical signal
How does an electron multipler (EM) detect ions?
- ions attracted to dyode
- electron released
- surface of dyode tube is covered in electron releasing material
- cascade event occurs (10^6 multiplication of original ion)
How does the micro-channel plate array detect electrons?
Thousands of electron multipliers connected together with multiple ions striking them.
Allows for simultaneous detection of different m/z
Why are Quadrapoles and electron impact used in tandem?
Their strengths and weaknesses complement each other as EI fragments no not require high performance to be detected.
Good for GC as they are organic volatile small Mwt molecules
Why are MALDI and TOF used in tandem?
-MALDI has high Mwt limit and TOF is unlimited – good combination.
-1 femtomole detection
Hence good for finger printing complex polymer mixtures
Why would the combinations of ESI/QP/IT/OT or ESI/QP/TOF be used?
Useful for multiply charged molecules like peptides and proteins.
What source can FT-ICR be fitted with?
All types of sources
What is the usual way of looking at polymers under mass spec?
Use soft ionisation method to produce a molecular ion.
Followed by a hard ionisation/tryptic digest to produce fragment ions
ESI and MALDI produce pseudo molecule ions. What does this mean?
Molecules with charging counter ion added (Na or proton).
e.g.
MALDI –> [M+H]+, [M+Na]+, [M-H]-
ESI –> [M+H]^n+, [M+Na]^n+, [M-H]n-
Atomic weights are scaled relative to what?
12^C
What is the nominal mass?
The mass calculated using an integer mass
If 2 molecules have the same nominal mass and different atomic compositions is it likely that have the mass accurate mass?
No, there is a high probability that the accurate masses are different
When are peaks considered fully resolved?
When at 10% of the maximum height of the peak you can still see two distinct peaks.
What is the calculation for mass accuracy?
Mass accuracy = difference between nominal and accurate/the accurate mass.
Low mass accuracy = a good mass accuracy
What is the calculation for the relative mass accuracy?
Relative mass accuracy = difference/accurate mass X 10^6 (give as part per million).
