atomic spectroscopy

Question 1

what are the 4 methods?

Answer 1

Flame photometry – AES

Atomic absorption – AAS

Atomic Fluorescence

Inductively coupled plasma – ICP

Question 2

what do the methods specifically deal with?

Answer 2

atoms not molecules

Question 3

the methods are used for the determination of what

Answer 3

the concentration of articular metal elements within a sample

Question 4

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

Answer 4

72

Question 5

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

Answer 5

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

Question 6

in energy level diagrams, wavelengths are given by what

Answer 6

figures/numbers

Question 7

in energy level diagrams, atomic orbitals are labelled by what

Answer 7

3s, 3d etc

Question 8

in energy level diagrams, electronic transitions are represented by what

Answer 8

the lines between orbitals

Question 9

sample prep and analysis - the flame

Answer 9

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

Question 10

what does sample prep and analysis involve

Answer 10

turning the liquid sample into an atomic gas

Question 11

sample prep and analysis - desolvation

Answer 11

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

Question 12

sample prep and analysis - vaporisation

Answer 12

the solid sample vaporises to a gas

Question 13

sample prep and analysis - atomisation

Answer 13

The compounds making up the sample are broken into free atoms

Question 14

detection and quantification - analysis

Answer 14

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

Question 15

see powerpoint for

Answer 15

maximum flame temps

Question 16

the burner - nebulizer

Answer 16

liquid breaks into fine mist

Question 17

the burner - glass bead

Answer 17

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

Question 18

the burner - aerosol

Answer 18

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

Question 19

the burner - fuel

Answer 19

usually acetylene

Question 20

the burner - oxidant

Answer 20

usually air

Question 21

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

Answer 21

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

Question 22

what happens to excess liquid in the burner

Answer 22

flows out into a drain

Question 23

what does AES stand for

Answer 23

atomic emission spectroscopy

Question 24

AES - the instrument

Answer 24

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

Question 25

where does atomic emission in flame photometry com from?

Answer 25

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

Question 26

in AES is a lamp used or not

Answer 26

no

Question 27

emission intensity is proportional to what

Answer 27

the concentration of the element in the sample

Question 28

what is AES most useful for

Answer 28

the determination of Na, K, Li, Ca

Question 29

does AES allow quantitative or qualitative analysis

Answer 29

both

Question 30

what does AAS stand for

Answer 30

atomic absorption spectroscopy

Question 31

how are electrons in the flame promotes to higher orbitals

Answer 31

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

Question 32

the absorbance is proportional to what in AAS

Answer 32

the concentration of the element in the sample being measured

Question 33

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

Answer 33

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

Question 34

what is the light source in AAS

Answer 34

a lamp whose cathode is composed of the element being measured

Question 35

what does the aspirator tube do in AAS

Answer 35

sucks the sample into the flame in the sample compartment sample is vaporised in the flame

Question 36

what is the sample holder in AAS

Answer 36

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

Question 37

sample compartment - AAS

Answer 37

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.

Question 38

how is the flame arranges in AAS

Answer 38

laterally long (10cm) not deep beam of light is focused through this flame as its longest axis onto a detector past the flame

Question 39

how is the height of the flame controlled in AAS

Answer 39

by controlling the flow of the fuel mixture

Question 40

how is quantitative analysis achieved in AAS

Answer 40

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

Question 41

how can you determine an unknown conc in AAS

Answer 41

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

Question 42

name 3 limitations of flame ionisation sources

Answer 42

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

Question 43

what are interferences

Answer 43

any effect that changes the signal while analyte conc remains unchanged

Question 44

how are interferences corrected

Answer 44

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

Question 45

what is spectral interference

Answer 45

unwanted signals overlapping analyte signal see notes for example

Question 46

what is chemical interference

Answer 46

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

Question 47

what is ionisation interference

Answer 47

ionisation of analyte atoms decreasing the concentration of neutral atoms