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Analytical Chemistry > atomic spectroscopy > Flashcards

atomic spectroscopy Flashcards

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1
Q

what are the 4 methods?

A

Flame photometry – AES

Atomic absorption – AAS

Atomic Fluorescence

Inductively coupled plasma – ICP

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2
Q

what do the methods specifically deal with?

A

atoms not molecules

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3
Q

the methods are used for the determination of what

A

the concentration of articular metal elements within a sample

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4
Q

how many different elements are the methods capable of analysing in solution

A

72

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5
Q

The transitions of atoms between their electronic fundamental and excited states, occur either by the effect of

A

the heat of the flame –> atomic emission spectroscopy – AES

an excitation light –> atomic absorption spectroscopy – AAS

laser excitation –> atomic fluorescence spectroscopy – AFS

argon torch –> inductively coupled plasma – ICP

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6
Q

in energy level diagrams, wavelengths are given by what

A

figures/numbers

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7
Q

in energy level diagrams, atomic orbitals are labelled by what

A

3s, 3d etc

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8
Q

in energy level diagrams, electronic transitions are represented by what

A

the lines between orbitals

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9
Q

sample prep and analysis - the flame

A

The sample is aspired into the flame (T = 1500 – 3000 C)

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10
Q

what does sample prep and analysis involve

A

turning the liquid sample into an atomic gas

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11
Q

sample prep and analysis - desolvation

A

The liquid solvent is evaporated, and the dry sample remains in the flame

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12
Q

sample prep and analysis - vaporisation

A

the solid sample vaporises to a gas

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13
Q

sample prep and analysis - atomisation

A

The compounds making up the sample are broken into free atoms

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14
Q

detection and quantification - analysis

A

The flame is the sample holder (as the cuvette is for UV) allowing the analysis to take place. The signal received from the ions allows the quantification

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15
Q

see powerpoint for

A

maximum flame temps

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16
Q

the burner - nebulizer

A

liquid breaks into fine mist

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17
Q

the burner - glass bead

A

Spray is directed at high speed against glass beads, upon which the droplets break into even smaller particles

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18
Q

the burner - aerosol

A

A fine suspension of liquid (or solid) particles in a gas

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19
Q

the burner - fuel

A

usually acetylene

20
Q

the burner - oxidant

A

usually air

21
Q

in the burner, the mist, fuel and oxidant do what

A

flow past baffles that promote further mixing and block large droplets of liquid

22
Q

what happens to excess liquid in the burner

A

flows out into a drain

23
Q

what does AES stand for

A

atomic emission spectroscopy

24
Q

AES - the instrument

A

the flame is the sample holder, where the heat promotes atoms to the excited state which then return to the fundamental state by realising a photon of a specific wavelength

25
Q

where does atomic emission in flame photometry com from?

A

atoms that are in an excited state because of the high thermal energy of the flame

26
Q

in AES is a lamp used or not

A

no

27
Q

emission intensity is proportional to what

A

the concentration of the element in the sample

28
Q

what is AES most useful for

A

the determination of Na, K, Li, Ca

29
Q

does AES allow quantitative or qualitative analysis

A

both

30
Q

what does AAS stand for

A

atomic absorption spectroscopy

31
Q

how are electrons in the flame promotes to higher orbitals

A

by absorbing a set of energy

this amount of energy is specific to a particular electron transition in each particular element

32
Q

the absorbance is proportional to what in AAS

A

the concentration of the element in the sample being measured

33
Q

in AAS, as the temperature of the flame is not hight enough to promote all atoms to their excited states, how is this done?

A

by the light supplied by the hallow cathode

cathode light is then absorbed by the atoms and the absorption spectrum is recorded at a specific wavelength

34
Q

what is the light source in AAS

A

a lamp whose cathode is composed of the element being measured

35
Q

what does the aspirator tube do in AAS

A

sucks the sample into the flame in the sample compartment

sample is vaporised in the flame

36
Q

what is the sample holder in AAS

A

it is the flame since it is in the flame that the atoms absorb radiation from the source

37
Q

sample compartment - AAS

A

The flame gases flowing into the burner create a suction that pulls the liquid into the small tube from the sample container. This liquid is transferred to the flame where the ions are atomized. These atoms absorb light from the source.

38
Q

how is the flame arranges in AAS

A

laterally long (10cm)

not deep

beam of light is focused through this flame as its longest axis onto a detector past the flame

39
Q

how is the height of the flame controlled in AAS

A

by controlling the flow of the fuel mixture

40
Q

how is quantitative analysis achieved in AAS

A

by measuring the absorbance of a series of solutions of known concentration

41
Q

how can you determine an unknown conc in AAS

A

a calibration curve and the equation for the line based on its absorbance

42
Q

name 3 limitations of flame ionisation sources

A

flame techniques can only detect one element at a time

the optimum excitation condition can vary widely from element to element

these techniques are not useful to analyse compounds which are highly resistant to decomposition by heat

43
Q

what are interferences

A

any effect that changes the signal while analyte conc remains unchanged

44
Q

how are interferences corrected

A

by removing the source of interference or by preparing standards that exhibit the same interference

45
Q

what is spectral interference

A

unwanted signals overlapping analyte signal

see notes for example

46
Q

what is chemical interference

A

chemical reactions decreasing the concentration of analyte atoms

caused by any sample that decreases the extent of atomisation of analyte

releasing agents are chemicals are added to a sample to decrease chemical interference

47
Q

what is ionisation interference

A

ionisation of analyte atoms decreasing the concentration of neutral atoms

Analytical Chemistry (17 decks)

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