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Separation Techniques > Mass Spectrometry > Flashcards

Mass Spectrometry Flashcards

1
Q

What steps may be required to prepare samples for MS?

A

Sample prep:
homogenization, dry/weigh, extraction (LLE, LPME, SPE…), purification/clean up, preconcentration, chem. modification (if needed)

separation:
LC, GC, IC, CE, FFF…

*or can be direct analysis

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2
Q

How is exact atomic mass different from the molecular mass?

A

molecular mass is AVERAGE from relative abundance of various natural isotopes

each natural isotope for a element will have a different exact mass

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3
Q

What are the most abundant forms of H, C, N, O, and S?

A

1H, 12C, 14N, 16O, 32S

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4
Q

What is the y and x axis in a mass spectrum?

A

y axis: relative intensity

x axis: m/z

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5
Q

What is m/z?

A

mass to charge ratio

divide mass number of ion by charge number

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6
Q

What environment is necessary for mass spectrometry?

A

vacuum (10-5 to 10-8 torr)

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7
Q

What are the general parts of a mass spectrometer? (6)

A

inlet system (connect to GC, LC….)
vacuum system
ion source (produce gas-phase ions)
mass analyzer (ions separated according to m/z)
detector (collect/convert specific ions into electric signal w/ ion transducer)
computer/signal processor (control + collect/analyze data)

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8
Q

The MS is connected to the LC or GC or CE by the ___ ____

A

inlet system

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9
Q

Where are the ions separated in the MS?

A

Mass analyzer (separate according to m/z)

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10
Q

The detector will _____ ions with a certain ____, and convert into an electric signal using a ___ _____

A

collect
m/z
ion transducer

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11
Q

What are common ion sources for mass spectrometry? (5)

A

gas phase:

  • electron impact (EI)
  • Chemical ionization (CI)

Desorption:

  • Fast atom bombardment (FAB)
  • matrix assisted laser desorption/ionization (MALDI)
  • Electrospray ionization (ESI)
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12
Q

What is the method of ionization for EI? what type of spectra does it produce?

A

energetic electrons

fragmentation patterns

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13
Q

What is the method of ionization for CI? what type of spectra does it produce?

A

reagent gaseous ions

proton adducts, few fragments

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14
Q

What is the method of ionization for FAB? what type of spectra does it produce?

A

energetic atom beam

molecular ions and fragments

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15
Q

What ionization type produces proton adducts?

A

chemical ionization

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16
Q

What method of ionization uses high energy photons?

A

MALDI

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17
Q

what type of spectra does MALDI produce?

A

molecular ions, multiply charged ions

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18
Q

What ionization methods can produce multiply charged ions?

A

MALDI

ESI

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19
Q

What is the method of ionization for ESI? what type of spectra does it produce?

A

electric field produces charged spray, which desolvates

multiply charged molecular ions

20
Q

ESI can be in ___ or ___ mode

A

positive

negative

21
Q

describe the process of EI ionization:

A

hit molecular ion with electron (M + e-)
produces molecular ion
M+ + 2e-

*relaxation of M+ will result in some fragmentation

22
Q

What is EI ionization usually paired with? (separation technique)

A

GC

23
Q

What ions can ESI (positive mode) produce? (6)

A 
M+ (if it exists); 
[M+H]+
[M+2H]2+
[M+3H]3+
[M+NH4]+
[M+Na]+
24
Q

What ions can ESI (neg mode) produce?

A

deprotonation [M-H]-

25
Q

ESI is usually paired with ____ separation

A

LC

26
Q

What are common mass analyzers for MS? (6)

A 
Magnetic sector
double focusing
quadrupole
ion trap
ion cyclotron resonance
time-of-flight
27
Q

What are ‘mass filters?’

A

another name for mass analyzers

28
Q

What is the principle of magnetic sector mass filters?

A

deflect ions in magnetic field (trajectory depends on m/z value)

29
Q

What is double focusing?

A
  1. electrostatic focusing

2. magnetic field deflection

30
Q

What is the principle of quadrupole mass filters?

A

ion motion in dc and radiofrequency fields - only certain m/z ions pass through

31
Q

How do ion trap mass filters work?

A

store ions in space (defined by ring + end cap electrodes)

E field will sequentially eject ions (in increasing m/z order)

32
Q

How do ion cyclotron resonance mass filters work?

A

trap ions in cubic cell (from trapping voltage + mag field)

orbital frequency related inversely to m/z

33
Q

how do TOF mass filters work?

A

long tube with detector at end

equal kinetic energy ions enter drift tube -> different mass = different velocity/arrival time at detector

34
Q

Describe the general parts of a GC-quadrupole MS system

A 
GC:
carrier gas inlet
injection port
column
oven
transfer line
MS:
ion source (ex: EI)
focusing lenses
mass analyzer (quadrupole)
electron multiplier
data system
35
Q

What are the possible functions (modes) of a mass analyzer?

A
  1. SCAN mode
    continuously scan all masses of a mass range (complete mass spectrum)
  2. SIM mode
    monitor SPECIFIC m/z
    (selected ion monitoring to target specific mass fragments)
36
Q

What mass analyzer mode is selected for quantification of traces? Why?

A

SIM mode (selected ion monitoring)

more sensitive/selective

37
Q

How does a electrically neutral mobile phase/sample from the LC become charged for the MS?

A

ESI:
charged by applying high voltage in the nebulizer unit
(vaporized into ultra-fine charged droplets)
charges move to surface of droplets -> ions liberated from droplets -> go into MS

38
Q

What causes the droplets formed by ESI to dissipate into ions?

A

charges will move to surface to minimize coulomb repulsion -> ions can’t go anywhere in droplets, so they break free

39
Q

What is MS/MS known as?

A

tandem MS

40
Q

What is tandem MS?

A

2 consecutive MS analyzers; monitor parent-daughter transition of ion (second MS will further analyze for a fragment from the first MS)

41
Q

the selected fragment in the first mass analyzer is called the ___ ion, abbreviated as ____

A

parent/precursor

Q1

42
Q

The fragment resulting from fragmentation of the parent ion is called the _____ ion, abbreviated as ______

A

daughter/product

Q3

43
Q

Q1 -> Q3 is called a _________

A

parent-daughter transition

44
Q

monitoring several parent-daughter transitions to quantify analytes is called ___ ____ ____

A

multiple reaction monitoring (MRM)

45
Q

what is ‘resolution’ in MS?

A

Ability to distinguish 2 peaks of mass spectrum

resolution = M/(difference in m/z)

46
Q

What is ‘resolution’ in optical spectroscopy?

A

wavelength, wavenumber, or frequency difference of 2 still distinguishable lines in spectrum (related o spectral band width)

47
Q

What is the ‘valley’ definition of resolution in MS according to IUPAC?

A

10% Valley definition: 2 peaks w/ equal height in spectrum are separated by a valley w/ lowest point 10% of height of either peak

Separation Techniques (12 decks)

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