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acem > Lecture7-9 > Flashcards

Lecture7-9 Flashcards

0
Q

What is spectrometry?

A

Method used to acquire a quantitative measurement of the spectrum.
Practical application.

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1
Q

What is spectroscopy?

A

Science of studying interaction between matter and radiated energy.
Theoretical approach.

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2
Q

What is light?

A

Light is electromagnetic radiation which can be understood as an electromagnetic wave that travels through vacuum at the speed of light c and can be characterized by either its wavelength lenda or its frequency v.

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3
Q

Any material that can _____ light of a certain _____ will also _____ light of that _____

A

emit
wavelength
absorb
wavelength

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4
Q

What is atomic absorption?

A

Atomic absorption is the measurement of the absorption of optical radiation by atoms in the gaseous state.

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5
Q

3 forms of atomic spectroscopy?

A
  1. Atomic emission signal (–>monochromator–>detector)
  2. Atomic absorption, Hollow-cathode lamp
  3. Atomic fluorescence signal, Laser
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6
Q

What does the atomic emission transitions look like?

A

two arrows pointing downward.

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7
Q

How does atomic absorption transitions look like?

A

two arrows pointing upward.

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8
Q

How does atomic fluorescence transitions look like?

A

one arrow pointing up, two blue arrows pointing down (emission), one black arrow pointing down at excited states (nonradiative).

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9
Q

How does atomic absorption signal work?

A

Hollow cathode lamp - P0 - Flame - P - Monochromator - Detector - Amplifier - Computer

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10
Q

Formula to calculate Absorption A

A

Absorption A = log(Io/It) = kcd

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11
Q

AFS

A

Atomic Fluorescence Spectroscopy

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12
Q

Why AFS use more often than AAS?

A

AFS is often more sensitive than AAS because weak fluorescence signal can be observed above a dark background; not widely use.

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13
Q

AAS

A

Atomic Absorption Spectroscopy

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14
Q

Atomization

  • flame (____)
  • electrically heated ____ ____ (GFAAS) }
  • ____ ____ ____ (ICP) } of most practical relevance
  • heated quartz cell (____ ____)
A

FAAS
graphite furnace
inductively coupled plasma
hydride technique

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15
Q

Name of the tube that inject liquid to glass bead?

A

pneumatic nebulizer

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16
Q

Minimum amount of sample that is needed for FAAS?

A

1-2mL

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17
Q

Most common fuel oxidizer: ____/__
30 so-called ____ that from stable oxides -> need ____ flame to prevent this. Height in flame at which ___ atomic absorption/emission observed must be manually optimized and depends on:____, ____, ____

A

acetylene/air
“refractory elements” hotter maximum
element, fuel / oxidizer flow rate / nebulization speed

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18
Q

Graphite furnaces: electrically heated ____ can also be used to generate atoms from sample analyte.
Advantages? (2 of them)

A

hollow graphite tube

  1. less sample needed (5-100uL)
  2. more sensitive than flame
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19
Q

How long do atoms in the ground state reside in optical path? also called ____?

A

flame < 1s

furnace: several seconds b/c atomic “cloud” confined by tube

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20
Q

How are atoms generated? What must be carefully optimized? What should be carefully for first step and second step?

A

dry - ash - atomize - clean - cool
temperature
avoid splatter
no analyte loss

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21
Q

Ar gas passed through graphite tube, typical temperature program:

A

dry: 60C for 20s (remove solvent)
ash: 1400C for 60s (destroy organic matter)
atomize: (2300C for 6s)
clean: 2700C for 3s + cool (60s)

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22
Q

For elements that form _____ with carbon from the tube, use ____

A

carbides

pyrolytically deposited carbon tubes

23
Q

Additional advantages of furnace:

A
  1. pre-concentration
  2. analyze solid samples
    (impossible with flame)
24
Q

Everything other than analyte in sample = _____, ideally _____ decomposes and vaporizes during ashing if ____ constitutes a problem -> need to add a _________, to increase volatility of ____ and decrease volatility of _____.

A

matrix matrix matrix
matrix modifier
matrix analyte

25
Q

NaCl + NH4NO3 = NaNO3 + NH4Cl, it’s called ____

A

sublime (at 400C)

26
Q

Other matrix modifiers: Pd(NO3)2, added to seawater to ____ volatility of Sb: without modifier 90% of Sb lost during ____ step at 1250C; with the ______ seawater matrix can be evaporated at 1400C without loss of Sb.

A

decrease

matrix modifier

27
Q

Other matrix modifiers: Mg(NO3)2, raise ____ temperature of Al at high temperature of Al ____ by MgO (g). 3MgO(g) + 2Al(s) -> 3Mg(g) + Al2O3(s) when all MgO(g) evaporated reaction no longer occurs and Al2O3 decomposes.

A

atomization

retarded

28
Q

______ increases boiling point of ____ -> higher ____ temperature can be used without losing analyte.

A

matrix modifier
analyte
ashing

29
Q

Inductively coupled plasma: induction coil connected to a high ____ current generator -> generates ____ magnetic fields ____ oriented inside coil -> Tesla discharge ______ ionizes Ar -> free e- accelerated by _____ collide with ____ and ____ + transfer energy to entire gas (6000-10000K)

A

frequency oscillating
axially ignition
radio frequency field
atoms ions

30
Q

Advantage of ICP: high temperature, _____ + _____ inert Ar environment, this eliminates _____ (flame), allows _____ multielement analysis.

A

stability relatively
interferences
simultaneous

31
Q

Heated quartz cell (hydride technique) advantage: _____ and _____ of analyte and complete _____ of interferences.

A

separation enrichment

elimination

32
Q

How temperature affects atomic spectroscopy: temperature determines: 1. ____ to which sample breaks down (FAAS/GFAAS) 2. ____ to which atom found in ____/____/____

A

degree
extent
ground/excited/ionized state

33
Q

Boltzmann distribution describes _______ of different states at _______.
If _____ exists, _________ (N*/N) of any two states is _________.
k (Boltzmann’s constant) = _____

A 
relative populations 
thermal equilibrium
equilibrium   relative population
N*/No = g*/go *e^(-delta E/kT)
k = 1.381*10^(-23) J/K
34
Q

Critical in atomic emission spectroscopy that ____ is very stable or _______ will vary significantly.

A

flame

emission intensity

35
Q

Instrumentation: atomic line widths. Beer’s Law requires that _____ of _______ must be narrower than _____ in atomic sample vapor, otherwise measured _____ not be _____ to sample concentration.

A

linewidth radiation
linewidth absorbance
proportional

36
Q

Linewidth governed by ______

A

Heisenberg uncertainty principle

37
Q

Hollow cathode lamp: _____ cannot isolate lines narrower than _____-> produce narrow lines with correct lenda, we use hollow cathode lamps.

A

monochromators

10^(-3) - 10^(-2)

38
Q

Hollow cathode lamp made of element we want to analyze for:1. when 500V applied -> gas ____ and + ions accelerated toward ____2. lamp maintained at ____ 3. ____ strike cathode -> metal ____ into gas phase -> gaseous atoms collide with high energy electrons to ____ protons 4. atoms in lamp lamp emission narrower

A

ionized cathode
2-30mA cations
sputtered emit
flame

39
Q

multi-element detection with inductively coupled plasma: an ______ does not require any ____ and can measure as many as ___ elements simultaneously.

A

ICP-AES
lamps
70

40
Q

two types of configurations

A
  1. color plate

2. box purged with Ar to exclude O2 to observe lenda 100-200nm halogens + S,P,C and N

41
Q

Standard solutions for FAAS not necessarily suitable for _____ techniques and GFAAS: need extremely pure water and ___ to avoid contamination (_____, ____); clear room conditions (no dust). Standard solutions have limited ____ and _____ will change the _____ over time.

A

ICP-based aids trace metal grade acids, Teflon vessels
shelf life evaporation concentration

42
Q

Definition of interference?

A

any effect that changes signal while analyte concentration remains unchanged.

43
Q

_____ interference: _____ reactions decreasing [ ] of analyte atoms.
_____ interference: _____ of analyte atoms dereasing [ ] of neutral atoms. Desired signal is ____.

A

Chemical chemical

Ionization ionization decreased

44
Q

Virtues of inductively coupled plasma: eliminates many common ____: two times as hot as flame, _____ more complete and intense and no formation of ______.

A

interferences
atomization
refractory oxides/hydroxides

45
Q

____ remarkably free of background radiation. _____ is a problem in FAAS, but not in ____ because _____ more uniform.

A

plasma
self-absorption
ICP
temperature

46
Q

ICP-AES: atomization at > ____, dominant form today. In contrast to AAS and AFS _____ is needed. ______ proportional to analyte [ ] in sample.

A

6000K
no lamp
emission intensity

47
Q

ICP-MS: ionization energy of Ar: ___, ___ than that of all elements except He, Ne and F. Ar plasma: analyte elements ionized by ____ with Ar+ excited Ar atoms or energetic e-, direct plasma at MS, can measure ___ and ___ at very low [ ].

A

15.8eV greater collisions

metals metalloids

48
Q

matrix can have ____ effect on yield of ions generated in plasma: ___________ in same matrix as unknown -> ______

A

profound
calibration standards
standard addition

49
Q

_____ interference: interference by ___ of similar mass-to-charge ratio.
Use a high resolution _____ to resolve species.

A

isobaric
ions
ICP-MS

50
Q

What’s normal mass?

A

integer mass of most abundant isotope of each of the constituent atoms.

51
Q

MS = a technique for studying masses of ___/___/______: desorb ____ species; ____ them; ____ ions; separate ions according to ___/___ ratio; ____. If all species have a charge of +1, m/z is ___ to mass; if an ion has a charge of +2, m/z is ___ of mass.

A

atoms/ molecules/ fragments of molecules
gaseous ionize accelerate mass/charge (m/z) detection
equal half

52
Q

magnetic sector mass spectrometer formula:

A

m/z = eB^2r^2/2V

53
Q

EI stands for? e- emitted from a hot ____ accelerated, ___ electrons interact with incoming (neutral) molecules. ____ of molecules (M) absorb ____, enough for ionization.

A

electron ionization
filament 70eV
0.01% 12-15eV

54
Q

If we lower E in ______, _____ yield of ions + less ______, higher chance to observe M+. 70eV customarily used because it gives reproducible _____ that can be compared with spectra in a library. Most intense peak = _____. ____ of all other peaks expressed as % of _____

A

ionization source lower fragmentation
fragmentation base peak
intensities base peak intensity

55
Q

Resolving power: each mass spectral peak has ____, _____ how closely 2 peaks could be spaced and still be resolved the _____ the resolving power of a ___, better able to separate 2 peaks of similar mass.

A

width
limits
higher
MS

acem (11 decks)

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