atomic spectroscopy Flashcards
what are the 4 methods?
Flame photometry – AES
Atomic absorption – AAS
Atomic Fluorescence
Inductively coupled plasma – ICP
what do the methods specifically deal with?
atoms not molecules
the methods are used for the determination of what
the concentration of articular metal elements within a sample
how many different elements are the methods capable of analysing in solution
72
The transitions of atoms between their electronic fundamental and excited states, occur either by the effect of
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
in energy level diagrams, wavelengths are given by what
figures/numbers
in energy level diagrams, atomic orbitals are labelled by what
3s, 3d etc
in energy level diagrams, electronic transitions are represented by what
the lines between orbitals
sample prep and analysis - the flame
The sample is aspired into the flame (T = 1500 – 3000 C)
what does sample prep and analysis involve
turning the liquid sample into an atomic gas
sample prep and analysis - desolvation
The liquid solvent is evaporated, and the dry sample remains in the flame
sample prep and analysis - vaporisation
the solid sample vaporises to a gas
sample prep and analysis - atomisation
The compounds making up the sample are broken into free atoms
detection and quantification - analysis
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
see powerpoint for
maximum flame temps
the burner - nebulizer
liquid breaks into fine mist
the burner - glass bead
Spray is directed at high speed against glass beads, upon which the droplets break into even smaller particles
the burner - aerosol
A fine suspension of liquid (or solid) particles in a gas
the burner - fuel
usually acetylene
the burner - oxidant
usually air
in the burner, the mist, fuel and oxidant do what
flow past baffles that promote further mixing and block large droplets of liquid
what happens to excess liquid in the burner
flows out into a drain
what does AES stand for
atomic emission spectroscopy
AES - the instrument
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
where does atomic emission in flame photometry com from?
atoms that are in an excited state because of the high thermal energy of the flame
in AES is a lamp used or not
no
emission intensity is proportional to what
the concentration of the element in the sample
what is AES most useful for
the determination of Na, K, Li, Ca
does AES allow quantitative or qualitative analysis
both
what does AAS stand for
atomic absorption spectroscopy
how are electrons in the flame promotes to higher orbitals
by absorbing a set of energy
this amount of energy is specific to a particular electron transition in each particular element
the absorbance is proportional to what in AAS
the concentration of the element in the sample being measured
in AAS, as the temperature of the flame is not hight enough to promote all atoms to their excited states, how is this done?
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
what is the light source in AAS
a lamp whose cathode is composed of the element being measured
what does the aspirator tube do in AAS
sucks the sample into the flame in the sample compartment
sample is vaporised in the flame
what is the sample holder in AAS
it is the flame since it is in the flame that the atoms absorb radiation from the source
sample compartment - AAS
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.
how is the flame arranges in AAS
laterally long (10cm)
not deep
beam of light is focused through this flame as its longest axis onto a detector past the flame
how is the height of the flame controlled in AAS
by controlling the flow of the fuel mixture
how is quantitative analysis achieved in AAS
by measuring the absorbance of a series of solutions of known concentration
how can you determine an unknown conc in AAS
a calibration curve and the equation for the line based on its absorbance
name 3 limitations of flame ionisation sources
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
what are interferences
any effect that changes the signal while analyte conc remains unchanged
how are interferences corrected
by removing the source of interference or by preparing standards that exhibit the same interference
what is spectral interference
unwanted signals overlapping analyte signal
see notes for example
what is chemical interference
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
what is ionisation interference
ionisation of analyte atoms decreasing the concentration of neutral atoms
