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instrumental exam 2 > Mass Spec > Flashcards

Mass Spec Flashcards

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

A

3-300 amu

25
Q

resolution of a typical icp ms

A

1 amu

26
Q

dynamic range of the icp ms

A

10^6

27
Q

mass range of the agilent 7500

A

5-260 amu

28
Q

resolution of the agilent 7500

A

0.6 to 0.7 amu

29
Q

dynamic range of the agilent 7500

A

10^9

30
Q

2 general types of interferences in ms

A

spectroscopic and matrix

31
Q

two causes of spectroscopic interferences

A
  1. isobaric 2. polyatomic ions
32
Q

when is it most common for polyatomic ions to cause spectroscopic interferences

A

below a mass to charge ratio of 82

33
Q

plasma and atomosphere are examples of what type of intereference

A

spectroscopic

34
Q

plasma and matrix species are examples of what type of intereference

A

spectroscopic

35
Q

how can spectroscopic interferences be corrected?

A

a blank or the selection of different analytical isotopic mass

36
Q

when are matrix interferences noticeable

A

greater than 500 ppb

37
Q

how can matrix interference be corrected

A

diluting solutions and separating out the offending species

38
Q

2 general types of ion sources of ms

A

gas phase and desorption

39
Q

what does the gas phase ionization source do

A

vaporize sample

40
Q

what does the desorption ionization source do

A

convert to gas and then ionize

41
Q

3 types of gas phase ion sources

A

electron impact, chemical ionization, and field ionization

42
Q

3 types of desorption ion sources

A

matrix assisted desorption ionization, electrospray ionization, secondary ion mass spec

43
Q

what is a hard ionization source

A

breaks chemical bonds to get fragmentation

44
Q

what is a soft ionization source

A

low energy causes little fragmentation

45
Q

is electron impact (EI) soft or hard

A

hard

46
Q

is chemical ionization (ci) soft or hard

A

semi-hard

47
Q

is matrix assisted desorption ionization (maldi) soft or hard

A

soft

48
Q

is electrospray ionization (ei) soft or hard

A

soft

49
Q

is secondary ion mass spec (sims) soft or hard

A

soft

50
Q

in order to use a gas phase ionization source, the bp of the sample must be

A

below 500 degrees celsius

51
Q

are desorption sources used for liquid or solid

A

both

52
Q

how does the electron impact source work

A

bombard has phase molecule with electrons, electrons are lost, and a radical ion is formed, and fragmentation occurs

53
Q

3 advantages of the electron impact source

A

higher currents, increased sensitivity, and fragmentation

54
Q

2 disadvantages of the electron impact source

A
  1. molecules must be vaporized, and thermally stable. 2. weak or absent m+ peak
55
Q

how does the ci ion source work

A

reagent gas is bombarded with electrons and produces ions of reagent. ions collide with analyte molecule causing ions

56
Q

2 advantages of ci

A
  1. molecular ion survives, 2. simple spectra
57
Q

how does madli work

A

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
Q

how does esi work

A

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
Q

how does sims work

A

bombard sample surface with primary ion beam

instrumental exam 2 (6 decks)

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