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Analytical Chemistry > Exam II > Flashcards

Exam II Flashcards

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1
Q

Radio frequency

A

Spin flip in magnetic field
NMR-nuclear magnetic resonance
EPR/ESR- electron paramagnetic/spin resonance

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2
Q

Microwave

A 
Rotational energy (whole molecule)
Microwave spectroscopy-THZ spectroscopy
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3
Q

IR

A 
Vibrational energy levels (bonds) 
IR spectroscopy (dipole)
Raman spectroscopy (non dipole)
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4
Q

UV-vis

A

Electronic energy levels (valence)
UV-vis spectroscopy (absorbance)
Fluorescence (emission)

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5
Q

X-ray

A

Electron energy levels (core e-)

X-ray fluorescence

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6
Q

Gamma rays

A

Nuclear energy levels

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7
Q

Boltzmann distribution

A 
N1/n2=e^-(dE/KT)
dE-difference in energy levels
K- Boltzmann constant
T- temperature
N1/n2- ratio of amount at state 1 to 2
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8
Q

2 forms of spectroscopy

A

Absorbance/transmission

Emission

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9
Q

Beers law

A 
A=€bc
A- absorbance
€- molar absorbtivity
C- concentration
B- path length
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10
Q

Limits to beers law

A

Assume chromophores don’t interact
Assumes monochromatic light
No stray light

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11
Q

Absorbance instrumentation

A 
Source
Monochromator
Sample 
Detector
Readout device
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12
Q

Emission instrumentation

A 
Source
Excitation monochromator
Sample
90*
Emission monochromator
Detector
Readout device
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13
Q

Optical materials

A

Makes up lenses, mirrors, sample containers
IR: nacl, Kbr, csi, ge, znse
Vis: glass, plastic
UV: quartz, fused silica

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14
Q

Spectroscopy Sources

A 
Ir: thermal sources- nearnst glowers, nichrome wires, globar(heated wire gives off ir)
Vis: tungsten lamp
UV: deuterium lamp
Fluorescence: xenon arc lamp (UV-vis)
Lasers (emissions)
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15
Q

Continuum vs line source

A

Line- laser

Everything else is continuum

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16
Q

Monochromators

A 
Prism
- older
- less wavelength resolution
- resolution varies through spectrum
- spec 20
Grating
- newer, more expensive
-better resolution
- uniform resolution across spectrum
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17
Q

Spectroscopy Detectors

A

IR- thermal
-based on temp dependent electrical property
UV-vis- photon detectors
- amount of photons hitting detector

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18
Q

IR detectors

A

Thermocouples, bolometers, pneumatic cells (small gas filled chamber, measure expansion/contraction with dT)

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19
Q

UV-vis detectors

A

Photomultiplier tubes (photoelectric effect, older, bigger, good at low light, detect single photons)
Silicon based detectors (made from individual diodes, pn junction and DAD)
Pn junction ( little, relative e- to Si creates current)
DAD/diode array detector (measures entire spectrum simultaneously, less sensitive)
Charged coupled device/CCD (measure hv intensity)

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20
Q

Double beam instruments

A

Measure blank and sample simultaneously

Double beam in space vs. in time

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21
Q

Double beam in space

A

Monochromator sends light to reference and sample simultaneously, and to two detectors, and one read out

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22
Q

Double beam in time

A

Monochromator sends light to chopper which allows light o switch between reference and sample, light passes to combiner to single detector and readout

23
Q

Chromophores

A 
Conjugated substance
Widely applicable
Reasonably sensitive
Somewhat selective
Cheap and easy
24
Q

Fluorescence

A 
Highly conjugated
Structurally rigid
Quantum yield (fraction of absorbed photons that are re-emitted)
F=kc 
Highly selective
Very high sensitivity
25
Q

Column efficiency

A 
N=L/H=16(tr/w)^2
N- number of theoretical plates (lg=more efficient)
L- length of column
H- plate height
Tr- retention time 
W- column width
26
Q

Chromatograph vs. chromatogram

A

Graph-apparatus

Gram- data

27
Q

Gradient elation problems

A

Switch between optimal conditions
Hv-temp variant
Hplc- solvent comp

28
Q

GC

A 
Carrier gas tanks
Oven
(Sample injector
Column
Detector)
Readout
29
Q

GC Carrier gases

A

Helium, hydrogen, nitrogen

30
Q

GC Sample injector

A 
Split (part of sample)
Split less (all of sample)
31
Q

GC Columns

A

Packed (older, lg diameter, least efficient, larger sample sizes)
Capillary (newer, sm diameter, most efficient, smaller sample sizes)

32
Q

Ideal detector

A 
Sensitive
Stable and reproducible
Linear range across orders of magnitude
Operate 25-400*C
Short response time
Similar response to all analytes or highly predictable one to some
Nondestructive 
Easy to use/reliable
33
Q

GC detectors

A

FID- reduced carbons; oxidizes sample, releasing e- which create current; large linear range; medium high sensitivity
TCH- older, simple; detects change in thermal conductivity; nondestructive; low sensitivity
ECD- detect halogens, nitros,quinones, e- w/drawing; high sensitivity

34
Q

HPLC

A

solvent res, pump, sample injector, column, detector, read out

35
Q

HPLC Columns

A

normal phase- nonpolar solvent, polar column

reverse phase- polar solvent, nonpolar column

36
Q

HPLC detectors

A

UV-vis: mid sensitivity, needs chromaphore
fluorescence: high sensitivity, needs fluorophore
refractive index: least sensitive, universal

37
Q

GC vs HPLC

A

GC- limit by what can be in gas phase; HPLC- big and polar

38
Q

Mass spectrometry

A

sample inlet, ion source, mass analyzer, detector, read out

39
Q

sample inlet

A

probe that heats sample to gas phase

40
Q

MS detector

A

charged plate

41
Q

MS ion sources

A

ionize sample and determine sensitivity
electron implact- hard ionization, many frags, beam of e- to knock off e- from sample
chemical ionization- soft ionization, fewer frags, beam of ions that knock e- off sample

42
Q

MS mass analyzer

A

magnetic sector- oldest, r=mV/Bze
quadrupole- compact, fast, not super high mass resolution, limited mass range
time of flight- large mass range, simple, limited resolution and sensitivity, slow, use time to detector to determine m/z
ion trap- potential for higher mass res, FT mode, sample in cube of varying charged sides

43
Q

tandem MS

A

identifies isomers

separate M+ by m/z, then fragments of M+

44
Q

GC detectors

A

FID- reduced carbons; oxidizes sample, releasing e- which create current; large linear range; medium high sensitivity
TCH- older, simple; detects change in thermal conductivity; nondestructive; low sensitivity
ECD- detect halogens, nitros,quinones, e- w/drawing; high sensitivity

45
Q

HPLC

A

solvent res, pump, sample injector, column, detector, read out

46
Q

HPLC Columns

A

normal phase- nonpolar solvent, polar column

reverse phase- polar solvent, nonpolar column

47
Q

HPLC detectors

A

UV-vis: mid sensitivity, needs chromaphore
fluorescence: high sensitivity, needs fluorophore
refractive index: least sensitive, universal

48
Q

GC vs HPLC

A

GC- limit by what can be in gas phase; HPLC- big and polar

49
Q

Mass spectrometry

A

sample inlet, ion source, mass analyzer, detector, read out

50
Q

sample inlet

A

probe that heats sample to gas phase

51
Q

MS detector

A

charged plate

52
Q

MS ion sources

A

ionize sample and determine sensitivity
electron implact- hard ionization, many frags, beam of e- to knock off e- from sample
chemical ionization- soft ionization, fewer frags, beam of ions that knock e- off sample

53
Q

MS mass analyzer

A

magnetic sector- oldest, r=mV/Bze
quadrupole- compact, fast, not super high mass resolution, limited mass range
time of flight- large mass range, simple, limited resolution and sensitivity, slow, use time to detector to determine m/z
ion trap- potential for higher mass res, FT mode, sample in cube of varying charged sides

54
Q

tandem MS

A

identifies isomers

separate M+ by m/z, then fragments of M+

Analytical Chemistry (2 decks)

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