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CHEM286 > Atomic Spectroscopy > Flashcards

Atomic Spectroscopy Flashcards

(49 cards)

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1
Q

what types of atomic spectroscopy are there?

A
  • atomic absorption
  • atomic emission
  • atomic interference
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2
Q

what techniques fall under atomic absorption?

A
  • Flame AAS
  • Graphite furnace AAS
  • Vapor (hydride) Generation AAS
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3
Q

what techniques fall under atomic emission?

A

MP-AES
ICP-OES
X-ray Fluorescence

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4
Q

what techniques fall under atomic interference?

A

X-ray Diffraction

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5
Q

how does atomic absorption work?

A
  • absorption of energy causes an electron move to higher energy level (E2)
  • excited electron drops back to the ground state, emitting light at particular wavelength
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6
Q

how does atomic emission work?

A
  • if theres enough energy, the electron leaves the atom completely, leaving behind a positively charged ion
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7
Q

what 4 components make up atomic absorption spectroscopy techniques?

A
  • Lamp
  • Sample atomizer
  • Monochromator
  • Detector
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8
Q

what is the purpose of the lamp in AAS techniques?

A

the amp emits light for element of interest
- usually 1 lamp per element

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9
Q

what is the purpose of the atomizer in AAS techniques?

A

atomizer converts liquid sample into free atoms which absorb light energy

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10
Q

what is the purpose of the monochromator in AAS techniques?

A

the monochromator selects wavelength used for measurement
- many elements give same wavelength so lamp is essential

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11
Q

what is the purpose of the detector in AAS techniques?

A

detector measure light absorbed by free atoms

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12
Q

what is the primary light source used?

A

hollow cathode lamp (HCL)

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13
Q

how do hollow cathode lamps (HCLs) work?

A
  • lamp is filled with inert gas at low pressure
  • contains metal cathode, containing element of interest, and anode
  • high voltage is applied across anode & cathode - ionizing the fill gas
  • gas ions hit cathode & sputter cathode material is excited in glow discharge to emit radiation of sputtered material
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14
Q

how does the atomizer convert a liquid sample into free atoms?

A

it does this through a sequence of sequential steps:
- Solution
- Nebulization
- Desolvation
- Vaporization
- Atomization
- Excitation
- Ionization

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15
Q

whats the main limitation of the lamp?

A

each lamp is dedicated to a single element
- in some cases a few elements (up to 5-8) can be combined into a single lamp

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16
Q

how does flame AAS work?

A
  • sample is prepared as liquid and nebulized into the flame, where atomization occurs
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17
Q

what is used for the flame in flame AAS?

A

flame is produced by burning hydrogen, acetylene or other combustible gas

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18
Q

whatre the advantages of flame AAS?

A
  • short analysis time
  • good precision
  • cheap & easy to use
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19
Q

whatre the limitations of flame AAS?

A
  • low sensitivity
  • limited dynamic range; simplistic set-up
  • requires flammable gas; cannot be left
  • excessive amounts of dissolved solids must be removed; reduces sensitivity
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20
Q

why are organic molecules avoided in flame AAS?

Study These Flashcards
A

organic molecules emit different wavelengths & are usually highly flammable

21
Q

what does dynamic range mean?

Study These Flashcards
A

dynamic range refers to the range of workable concentration

22
Q

what alternatives are there to flame AAS?

Study These Flashcards
A
  • graphite furnace; V. slow but V sensitive
  • hydride generation; only for volatile hydrides
  • cold vapor techniques (Hg); most sensitive for Hg
23
Q

whatre the main areas of application of AAS?

Study These Flashcards
A
  • determination of trace metals / impurities
  • analysis of elements
  • discovery of elements of interest in ores/oil wells
  • quality control; food, petrochemical industry
24
Q

what shape does a calibration curve of AAS usually take?

Study These Flashcards
A

Usually straight/linear

25
when concentrations are near the LoD, what can be done?
usually requires multiple pass analysis where all of the samples are determined using the most sensitive set-up
26
whats the main principal difference between AAS and AES?
AES does not require specific lamps as all elements are excited together - meaning wavelengths must be separated instead
27
what 4 components make up AES techniques?
Sample intro Plasma atomizer Monochromator CCD detector
28
why is a flame not used in AES like in AAS? what is used instead?
because the flame is not hot enough to excite atoms thus, microwave plasma & inductively-coupled plasma are used for excitation - reaching sufficiently high temperature to excite all elements in sample
29
what is used as the plasma in Microwave Plasma-AES?
Nitrogen plasma > Argon - easier to run
30
how hot does nitrogen plasma get in MP-AES compared to flame AAS?
N2 plasma ~ up to 5,000 K Air-acetylene flame ~ up to 3,100 K
31
what is the role of the nitrogen plasma in MP-AES
the nitrogen plasma is used to desolvate, atomize & excite atoms in the liquid sample that have been nebulized into it
32
what is measured in AES?
the intensity of light emitted is measured using an optical detection at the characteristic wavelengths for each element of interest
33
whatre the advantages of MP-AES?
- safe (no flammable gas) - low operating costs; N2 readily available - no lamps required; polychromator - can identify & quantify virtually all metals & many metalloids - better performance than flame AAS; as atomic emission is quite strong
34
whatre the limitations of MP-AES?
- higher initial cost than flame AAS - more interferences than flame AAS; many e- cause noise and confusion - not as sensitive as graphite furnace or ICP-MS - not as productive as ICP-OES - no isotope determination
35
how is the plasma in MP-AES sustained?
by using axial magnetic & radial electrical fields
36
whatre the key applications of MP-AES?
- trace elements in geological samples - metals in soil extracts - major elements in food & beverages - analysis of petroleum, water & waste
37
what gas is used for plasma in ICP-OES? how hot does it get?
Argon inductively coupled plasma - up to 10,000 K
38
what is the Ar plasma in ICP-OES used for?
it is used to desolvate, atomize, and excite the atoms in the liquid sample that has been nebulized into it
39
what is measured in ICP-OES experiments?
the intensity of light emitted is measured using optical detection at characteristic wavelengths of the element of interest
40
whatre the advantages of ICP-OES?
- fastest sample throughput - simultaneous multi-element analysis (up to 73 elements) - wide dynamic range (sub-ppb to % level) - tolerates complex matrices - low Ar consumption - no flammable gas (tho cannot leave unattended as magnetic fields could shift & melt machine)
41
whatre the limitations of ICP-OES?
- higher initial cost than AAS or MP-AES (200K) - more spectral interferences; due to hotter plasma causing ionisation - not as sensitive as graphite AAS or ICP-MS - no isotope determination - also cannot measure; 2nd period elements, halogens & noble gases
42
what additional benefit does ICP-OES posses?
ICP-OES is capable of measuring both atomic and ionic emission - hence more wavelengths can be monitored these measurements can then be compared to standards to quantify element concentration in sample
43
what can be done in ICP-OES experiments to reduce spectral interferences?
ion-exchange chromatography can be done to separate mixture
44
whatre the key applications of ICP-OES?
- monitoring water & waste - determination of trace elements in water - mercury monitoring in environmental samples - quantitative analysis of multiple elements - analysis of soils; micronutrient content - determination of precious metals
45
what is the main difference between ICP-OES and ICP-MS?
main difference to ICP-OES is that ICP-MS analyzes atomic ions, not emission spectra
46
how does ICP-MS work?
- sample is ionized in argon ICP - ions then passed into high vacuum region for separation & detection - photons and neutral species are rejected - mass spectrometer separates ions based on their mass-to-charge ratio (m/z)
47
whatre the advantages of ICP-MS?
- most sensitive technique; ppt - multi-element analysis - isotopic information - wide dynamic range - tolerates complex matrices
48
whatre the limitations of ICP-MS?
- lower matrix tolerance than ICP-OES - most expensive technique (500k) - subject to isobaric interferences - machine must also be used regularly to keep machine alive - also must clean regularly or MS will break
49
what range of isotopes can ICP-MS measure?
ICP-MS measures characteristic isotopic mass of elements from 6Li to 238U

CHEM286 (6 decks)

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