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MLSCI 466 Final > liquid chromatography and mass spec > Flashcards

liquid chromatography and mass spec Flashcards

1
Q

difference of isocratic and gradient mode in LC

A

isocratic = mobile phase composition is the same every run

gradient = mobile phase changes throughout the run

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2
Q

what causes separation of anaylte bt mobile and stationary phase

A

differential equilibrium aka partition coefficient

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3
Q

what is another name for partition chromatography

A

liquid liquid chromatography bc both mobile and stationary are liquid

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4
Q

purpose of a column in LC

A

prevent dissolution of stationary phase by covalent binding solica

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5
Q

explain normal and reverse phase LC column

A

normal phase - stationary phase is more polar than mobile phase

reverse phase - mobile phase more polar than stationary

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6
Q

two most common solvents use in LC

A

methanol
acetonitrile

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7
Q

what is considered when choosing a solvent

A

polarity and UV cut-off

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8
Q

purpose of buffers

A

control pH (selectivity)
reduce peak tailing
give well shaped peaks

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9
Q

What should the buffers pH be

A

+/-1 of buffer’s pKa

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10
Q

are volatile or non volatile buffers preferred in LC-MSMS

A

Volatile because non volatiles contaminate ion source

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11
Q

Thoery of UV detector

A

UV and photometers with intense light sources are quantified using beers law

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12
Q

theory of electrochemical/amperometric detector

A
  1. effluent passes voltage electrode
  2. large voltage = movement of electrons = current
  3. current is proportional to concentration of analyte
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13
Q

what is voidtime (to)

A

time to elute unretained substance

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14
Q

what is retention time

A

time elasped from injection of sample to recording of peak

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15
Q

what value is good resolution

A

1.25 or greater

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16
Q

what factors affect peak retention and peak width

A

retention
- capacity factor (k)
- selectivity (a)

width
- efficiency (N)

17
Q

what does capacity factor (k) measure and how to adjust it

A

retention time - change organic solvent

18
Q

what does selectivity factor (a) measure

A

retention time of two peaks - most important factor

19
Q

what does efficiency factor (N) measure and how

A

peak width - calculate number of theoretical plates

20
Q

why is selectivity the most imporant factor for resolution

A

selectivity is a function of column packing, mobile phase, and solute chemistry

21
Q

what does a large number of theoretical plates mean

A

narrow peaks = efficient column

22
Q

what factors increases efficiency (narrower peaks)

A

well packed and lengthy column

increasing flow rate

less volume injected

23
Q

why are samples extracted before injection

A

-prolong life of column
- peaks of interest
-improve sensitivity

24
Q

what does mass spec detect

A

fragmentation patterns

25
Q

theory of ionization -electron impact- in mass spec

A
  1. electron beam of 70eV from a heated filament onto ion source
  2. sample loses e- (unstable) = fragmentation
  3. voltage on repeller plate causes ions to be accelerated to analyzer
26
Q

what is a quadrupole

A
  1. mass analyzer
  2. four rods (dc and rf voltages)
27
Q

what is the path of mass spec

A
  1. inlet
  2. ionization (electron impact)
  3. mass analyzer (quadrupole)
  4. detector and data
28
Q

what is the molecular ion and base peak

A

molecular ion = largest m/z peak

base = most abundant peak

29
Q

problems of gc mass spec

A

heat labile compounds; methadone

acetaminophen has poor chromatographs

30
Q

full scan vs SIM (select ion monitoring)

A

full scan = every ion

SIM = derivitization step for selected ions (increase sensitivity)

31
Q

what is deuterated internal standard

A

3 hydrogen replaced with deuterum for controls

32
Q

pros and cons of LC MS

A

pro
- LC is good for volatile and non volatile (GC only uses volatiles)

  • LC works with polar analytes (GC is poor extraction with polar)

con
- Ion suppression with high salt

33
Q

steps in electrospray ionization

A
  1. form charged droplets
  2. evaporation
  3. ionic repulsion
  4. ion enter mass analyzer
34
Q

what happens in triple quadrupole (tandem) MS

A

Q1 = single m/z selection
Q2 = fragmentation in collision cell
Q3 = single m/z selection to the detector

35
Q

principle of QTOF MS

A

separation of m/z by TOF
-smaller = faster
- heavier = slower

Q1= filter
Q2= fragmentation
TOF = separation of ions

MLSCI 466 Final (4 decks)

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