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AES Flashcards

1
Q

radiative excitation

A

excitation by absorption of radiation

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2
Q

nonradiative excitation

A

Excitation by the application of thermal, electrical, or chemical energy

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3
Q

how is energy converted to kinetic energy in non radiative relaxition

A

collision with other atoms or minor molecules

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4
Q

what does molecular collision in nonradiative relaxation result in

A

minor increase in temperature

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5
Q

what results when radiative relaxation occurs after radiative excitation

A

Atomic fluorescence

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6
Q

what results when radiative relaxation occurs after nonradiative excitation

A

Atomic emission

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7
Q

atomic emission spectrometry methods

A

Atomic fluorescence spectrometry (AFS)
flame-AES
plasma-AES
Arc and spark-AES

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8
Q

what are AES methods classified by

A

excitation source

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9
Q

fluorescence

A

emission of a photon after radiative excitation of an atom

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10
Q

instrument components of AFS

A
  • source
  • excited wavelength selector
  • atomizer
  • emission wavelength selector
  • transducer
  • data processor
  • readout
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11
Q

why are AFS instruments set up at 90 degree angle

A

so the source doesn’t go to the detector, since we want the fluorescence not absorbance

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12
Q

resonance fluorescence

A

one wavelength in, same wavelength out

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13
Q

non-resonance fluorescence

A

one wavelength in, different wavelength out

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14
Q

what should radiation sources in AFS be

A
  1. linear

2. have high intensity

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15
Q

as source intensity increases the higher the ___

A

sensitivity

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16
Q

common linear sources in AFS

A
  1. Hollow cathode lamp (HCL)
  2. Electrode-less discharge lamp (EDL)
  3. lasers
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17
Q

issues with HCL in AFS

A

not as intense, therefore not as sensitive

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18
Q

what is the most common lamp for AFS

A

EDL

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19
Q

Laser advantages for AFS

A
  • high intensity

- Narrow band widths

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20
Q

Laser disadvantages for AFS

A
  • high cost

- operational complexity

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21
Q

Atomizers in AFS

A
  1. flames
  2. graphite furnaces
  3. plasma
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22
Q

Wavelength selectors in AFS

A
  1. Filters

2. Monochromators

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23
Q

Transducers in AFS

A
  1. Vacuum phototunes
  2. photomultiplier tubes (PMT)
  3. silicon diode transducers
  4. photodiode array (PDA)
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24
Q

Which is more common for AFS: qualitative or quantitative analysis

A

quantitative

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25
Q

Example of AFS application

A

determining metals in:

  • lubricating oils
  • seawater
  • geological samples
  • metallurical samples
  • environmental samples
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26
Q

what does Flame- atomic emission spec (F-AES) measure

A

photons emitted from atoms excited in a flame

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27
Q

Instrumentation components of F-AES

A
  • neutralizer
  • flame
  • wavelength selector
  • transducer
  • signal processor
  • readout
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28
Q

wavelength selectors for F-AES

A
  1. Flame photometer (filter)

2. Flame Spectrophotometer (monochromator)

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29
Q

qualitative analysis for F-AES

A

coupled with PDA, F-AES can be used to determine if the elements we’re interested in are present in our sample

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30
Q

which elements will F-AES excite

A

earth alkaline metals

alkali metals

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31
Q

Are internal standards essential for F-AES

A

yes bc the compensate for several types of error in emission spec

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32
Q

where is F-AES used

A

in the routine measurement of alkali and alkaline earth metals in materials such as biological and food samples

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33
Q

three channel flame photometer

A

two elements are analyzed, with 1 internal standard simultaneously (ie, analyzing Na and K and using Li as internal standard)

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34
Q

what is P-AES

A

plasma atomic emission spectroscopy (excitation by plasma)

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35
Q

what is plasma

A

an electrically conducting gaseous mixture containing a significant concentration of cations and electrons with a net charge of 0

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36
Q

power sources in P-AES

A
  1. inductively coupled plasma (ICP)
  2. Direct current plasma (DCP)
  3. Microwave induced plasma (MIP)
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37
Q

what source is ICP

A

radio frequency source

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38
Q

what source is DCP

A

direct current electrical source

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39
Q

what source is MIP

A

microwave frequency source

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40
Q

how is ionization initiated in ICP

A

ionization of Ar is initiated by a spark from a Tesla coil

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41
Q

what occurs in the induction coil of ICP

A

interations of the resulting ions from the Ar ionization, and electrons with the fluctuating magnetic field (H). This causes ions and electrons within the coil to flow in the closed annular path

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42
Q

what causes ohmic heating of the plasma

A

the resistance of the ions and electrons that flow int he induction coil

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43
Q

what are the common devices for sample introduction in ICP

A
  1. Pneumatic nebulizers
  2. Ultrasonic nebulizers
  3. electrothermal vaporization
  4. laser ablasion
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44
Q

which devices introduce liquid samples to ICP

A
  1. pneumatic nebulizers
  2. ultrasonic nebulizers
  3. electrothermal vaporization
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45
Q

which devices introduce solid samples to ICP

A
  1. electrothermal vaporization

2. laser ablasion

46
Q

advantages of electrothermal vaporization

A
  • µL sampling
  • low detection limit
  • wide working range
  • decent precision (5-10%)
  • free of interference
  • multi-element capabilities
47
Q

Typical laser(s) used in laser ablasion

A

Nd-YAG

48
Q

Why is the core not good for excitiation

A

too hot

49
Q

what is bremsstrahlung

A

continuum radiation produced when charged particles are slowed or stopped

50
Q

temperature and height of secondary region of plasma

A

10-30 mm above core

6000-6500 K

51
Q

why is a higher temperature good for ICP

A

since we need atomization and excitiation, a higher temperature means we can analyze more elements

52
Q

how long do samples reside in the plasma

A

2-3 ms

53
Q

why is a uniform temperature cross section beneficial in ICP?

A

self-absorption and self-reversal effects do not occur as often and calibration curves are linear over several orders of magnitude of concentration

54
Q

why is high electron density beneficial in ICP?

A

less ionization interference, therefore no need for ionization suppressor

55
Q

what causes the enhancement of the lifetime of an analyte in ICP

A

chemically inert environment in the plasma

56
Q

what gas is used is ICP

A

argon

57
Q

Why is there less self absorption in ICP

A

the plasma is optically narrow

58
Q

advantages of DCP

A
  1. significantly less argon needed
  2. auxiliary power supply is simpler and less expensive
  3. DCP is able to handle organic solutions and aqueous solution with a high solid content better that ICP
59
Q

Disadvantages of DCP

A
  1. Spectra produced has fewer lines than ICP and are often from atoms not ions, therefore there is less excitation
  2. lower sensitivities than ICP
  3. smaple volatilization is often incomplete with DCP nf short residence time (1 ms)
  4. optimal viewing region is small so optics have to be aligned correctly to magnify properly
60
Q

Main components of ICP-AES/ICP-OES

A
  1. Sampe introduction
  2. ICP source
  3. Wavelength selector
  4. Transducers
  5. Signal processor with readout
61
Q

wavelength selectors in ICP-OES

A
  1. Echelle grating
  2. Holographic grating
  3. Concave gratings
62
Q

Common transducers in ICP-OES

A
  1. photomultiplier tubes (PMT)
  2. photographic emulsions
  3. charge injection devices (CID)
  4. Charge coupled devices (CCD)
63
Q

why are two PMTs used in sequential ICP-OES instruments

A

one for UV and one for Vis

64
Q

why are multichannel spectrometers (polychromators) so beneficial for ICP-OES analysis

A

all elements can be detected simultaneously making for effective qualitative analysis

65
Q

chemical interferences with ICP-OES

A
  1. low matrix effects
  2. at low concentrations the background emission due to a recombination of argon ions with electrons is large enough to require careful corrections
66
Q

corrections for ICP-OES chemical inerferences

A

two-line method

67
Q

spectral interferences with ICP-OES

A
  1. line overlapping when spectra for multiple elements are rich in lines
68
Q

correction for ICP-OES spectra interference

A

use a suitable/ different line based on the components in the smaple

69
Q

can ICP-OES be used qualitatively or quantitatively

A

both

70
Q

what elements can be detected using ICP-OES

A

all metalic metals

71
Q

what range to B, P, N, S, and C need to be analyzed at

A

vacuum UV range (wavelength < 180 nm)

72
Q

why is there limited application for alkali metals

A

most predominate lines of these elements are located at near IR range which leads to difficulty in detection

73
Q

is it better to have more or less emission line

A

more bc better selection

74
Q

what plot is used for ICP-OES and why

A

log-log plot bc the dynamic range is so large

75
Q

internal standards are _____ used in ICPOES analysis

A

always

76
Q

what can be said about the detection limits of ICP-OES

A
  • better or comparable to other methods

- more elements can be detected at levels of 10 ppb or less with plasma excitation than with other methods

77
Q

how are elements excited in arc and spark AES

A

electric arcs or high voltage sparks

78
Q

where does excitation occur in arc and spark aes

A

int he gab between a pair of electrodes

79
Q

what provides the energy needed to atomize a sample and produce electronic excited states

A

passage of electricity that moves from the electrode to the gap

80
Q

Voltage of DC electric arcs

A

10-50 V

81
Q

current of DC electric arcs

A

1-30 A

82
Q

voltage of AC electric arcs

A

2200-4400 V

83
Q

current of AC electric arcs

A

1-5A

84
Q

why is the argon bewteen the two electrodes basically plasma?

A

bc it’s ionized

85
Q

how many sparks per half cycle of 60 Hz line current

A

4

86
Q

how many sparks per second

A

8

87
Q

what is the average current in a high-voltage spark

A

few tenths of an ampere

88
Q

in the initial phase of spark discharge, what may the instantaneous current exceed

A

1000 A

89
Q

During the initial phase what is the temperature of the streamer in the spark gap

A

40000 K

90
Q

what are lines emitted by ions usually called and why

A

“spark lines” bc it’s in spark but not arc

91
Q

is the number of lines in spark less or grater than the lines in arc

A

spark lines > # arc lines

92
Q

Arc and spark spec analysis is best for what

A

solids

93
Q

what metals are analyzed by arc and spard

A

metals or alloys

94
Q

what are the 2 electrodes made of in arc and spark while analyzing metals

A

one or both electrodes can be formed from the sample by milling or by casting the molten metal in a mold (at least one is the sample material)

95
Q

when an electrode is used against a flat polished surface in arc and spark, what are the electrode and flat polished portion made of

A

electrode: counter electrode made of graphite or metal rod

Flat surface: metallic sample

96
Q

what do we need in arc and spark analysis of nonmetallic saples

A

conductivity

97
Q

what is a nonmetallic supported in in arc and spark

A

electrode whose emission will not interfere with analysis

98
Q

why is carbon an ideal electrode for many arc and spark applications

A
  • can be obtained in highly pure form
  • good conductor
  • good heat resistance
  • easily shaped
99
Q

what shape is the electrode for sample holding in arc and spark

A

cylinder with a small cavity drilled into one side

100
Q

what samples can nonmetallic arc and spark analyze

A
  • powder

- liquid

101
Q

what is the counter electrode in nonmetallic arc and spark

A

tapered carbon rod with rounded tip

102
Q

what components are in arc and spark aes

A
  1. electrodes
  2. wavelength selector
  3. transducer
  4. signal processor and read out
103
Q

types of arc and spark instrumentation

A
  1. sequential

2. multichannel

104
Q

types of multichannel arc and spark aes

A
  • spectrographs

- spectrometers

105
Q

what are used in arc and spark spectrometers

A

PMTs

digital detectors

106
Q

three kinds of arc and spark applications

A
  1. qualitative
  2. quantitative
  3. semi-quantitative
107
Q

what arc and spark aes instrumentalists are used for qualitative analysis

A

multichannel

108
Q

in quantitative analysis which precision is poorer: arc or spark

A

arc

109
Q

are internal standards used in arc and spark aes

A

yes

110
Q

how does semi-quantitative arc and spark aes work

A

obtained concentrations are between 30-300% of real amounts because you don’t really care too much about how much is in there, just that you know a possible range

111
Q

applications of arc and spark aes

A
  • metallurical manufaturing
  • oil refineries
  • petrochemical and chemical industries
  • aviation
  • military
  • power plants
  • scrap sorting

analytical spectroscopy (3 decks)

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