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instrumental exam 2 > Mass Spec > Flashcards

Mass Spec Flashcards

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1
Q

Analysis steps of mass spec

A
  1. atomization, 2. ionization, 3. mass separation, 4. detection and processing
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2
Q

what happens in atomization

A

atoms or molecules made into a gas phase

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3
Q

what happens during ionization

A

the addition of energy to create singly charged positive ions

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4
Q

mass separation occurs based on what

A

mass to charge ratio

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5
Q

3 advantages of icp ms

A
  1. detection limits lower by 3 orders of magnitude 2. simple spectra 3. measurable isotopic ratios
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6
Q

3 disadvantages of icp ms

A
  1. expensive instrumentation 2. instrumental drift of 5-10%, 3. prone to interferences
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7
Q

components of a mass spec

A

inlet, gaseous ion source, mass analyzer, ion transducer, signal processor, mass spec (all in a vacuum)

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8
Q

4 types of atomic mass spec analyzers

A

quadrupole, double focusing ms, laser microprobe, secondary ion microbe

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9
Q

what allows the introduction of ions into the vacuum chamber

A

sampling cone, and skimmer cone

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10
Q

3 types of mass analyzers for icp ms

A
  1. quadrupole, 2. time of flight, 3. double focusing analyzers
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11
Q

mass range of a quadrupole mass analyzer

A

3000-4000

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12
Q

how does a quadrupole work

A

voltages of the same polarity are applied to opposing pole sets (stabilizing and destabilizing forces) and the ions are sequentially attracted and repelled allowing only certain ions to pass through

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13
Q

2 advantages of the time of flight mass anlyzer

A
  1. unlimited mass range, 2. lower resolution
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14
Q

How does a time of flight mass analyzer work

A

sample ions are accelerated to a uniform KE into the drift tube

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15
Q

what are the 2 devices for focusing the ion beam in the double focusing mass analyzer

A

electrostatic and magnetic

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16
Q

which mass analyzer has the highest resolution

A

double focusing

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17
Q

what are the the detectors of ms

A

electron multipliers and faraday cup

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18
Q

what are the two electron multipliers used as detectors for ms

A

discrete dynode, and continuous dynode

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19
Q

what is the current gain up to in the discrete dynode

A

107

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20
Q

what is the current gain up to in the continuous dynode

A

10^5 to 10^8

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21
Q

how does the faraday cup detector work

A

collected electrode is surrounded by a cage to prevent the escape of reflected ions and secondary electrons

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22
Q

what are the 2 advantages of faradays cup

A
  1. inexpensive, 2. electrically/mechanically simple
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23
Q

what are the three disadvantages of faraday’s cup

A
  1. needs high impedence amp 2. slower response time 3. less sensitive`
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24
Q

typical mass range of icp ms

25
resolution of a typical icp ms
1 amu
26
dynamic range of the icp ms
10^6
27
mass range of the agilent 7500
5-260 amu
28
resolution of the agilent 7500
0.6 to 0.7 amu
29
dynamic range of the agilent 7500
10^9
30
2 general types of interferences in ms
spectroscopic and matrix
31
two causes of spectroscopic interferences
1. isobaric 2. polyatomic ions
32
when is it most common for polyatomic ions to cause spectroscopic interferences
below a mass to charge ratio of 82
33
plasma and atomosphere are examples of what type of intereference
spectroscopic
34
plasma and matrix species are examples of what type of intereference
spectroscopic
35
how can spectroscopic interferences be corrected?
a blank or the selection of different analytical isotopic mass
36
when are matrix interferences noticeable
greater than 500 ppb
37
how can matrix interference be corrected
diluting solutions and separating out the offending species
38
2 general types of ion sources of ms
gas phase and desorption
39
what does the gas phase ionization source do
vaporize sample
40
what does the desorption ionization source do
convert to gas and then ionize
41
3 types of gas phase ion sources
electron impact, chemical ionization, and field ionization
42
3 types of desorption ion sources
matrix assisted desorption ionization, electrospray ionization, secondary ion mass spec
43
what is a hard ionization source
breaks chemical bonds to get fragmentation
44
what is a soft ionization source
low energy causes little fragmentation
45
is electron impact (EI) soft or hard
hard
46
is chemical ionization (ci) soft or hard
semi-hard
47
is matrix assisted desorption ionization (maldi) soft or hard
soft
48
is electrospray ionization (ei) soft or hard
soft
49
is secondary ion mass spec (sims) soft or hard
soft
50
in order to use a gas phase ionization source, the bp of the sample must be
below 500 degrees celsius
51
are desorption sources used for liquid or solid
both
52
how does the electron impact source work
bombard has phase molecule with electrons, electrons are lost, and a radical ion is formed, and fragmentation occurs
53
3 advantages of the electron impact source
higher currents, increased sensitivity, and fragmentation
54
2 disadvantages of the electron impact source
1. molecules must be vaporized, and thermally stable. 2. weak or absent m+ peak
55
how does the ci ion source work
reagent gas is bombarded with electrons and produces ions of reagent. ions collide with analyte molecule causing ions
56
2 advantages of ci
1. molecular ion survives, 2. simple spectra
57
how does madli work
the analyte is mixed with a matric, and a laser is used to irradiate the mix. the matrix absorbs laser energy. as a result, matrix molecules ionized, analyte and matrix vaporized
58
how does esi work
analyte solution pumped through a stainless steel capillary, and a spray of fine droplets that are charged by the electrode needle. the droplets evaporate, and the density increases. analyte with charge goes to detector
59
how does sims work
bombard sample surface with primary ion beam

instrumental exam 2 (6 decks)

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