electrons orbit the nucleus in discrete orbitals, but may move between orbitals but they must absorb/emit energy corresponding to the energy difference between orbitals
electrons become thermally excited and are promoted to higher energy states, they then relax back down to ground state by EMISSION of light
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Process of AES
electrons from the OUTER shell are promoted to higher energy state and then relax back down to ground state by the emission of light
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Instrumentation in AES (3)`
1. Flame 2. Monochromator 3. Detector
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Flame
Aq sample containing metal is volatilised by natural gas OR compressed air flame 2000 degrees. Flame will emit light + filter out filter out other WL.
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Monochromator
electrons will become excited from flame, promoted and relax back down with emission of light. This emitted light is filtered by the monochrom. It filters out WL of no interest
some atoms lose electrons at higher temp, this affects measurements taken
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Sample viscosity
organic sub can change sample viscosity which affects rate of transfer into the flame
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Anionic interference
anions from involatile salts can react with M ions. to decrease reading. Sol: add lanthanum chloride to ppt anions
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Atomic absorption spec
most heavy atoms cannot be excited - it would required too much energy , so instead we VOLATILISE metals atoms (not excite) in a flame
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Principle of AAS
Rad of specific WL is passed thru hollow tube through a flame. Tube is coated in metal to be analysed. Volatilised atoms will absorb rad equal to diff between ground an excited states
Hollow cathode lamp, coated in metal to be analysed. Diff lamps required for diff metals so only one element can be analysed at a time
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Flame
metal atoms volatilised by flame and rad is passed thru cathode and flame. Vol. atoms absorb rad equal to diff in energy between ground and excited states
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3. Monochromator
set to WL of interest will filter out all other WL . cuts out interference from other sources (flame)
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Detector
is a photosensitive cell
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AAS interfering factors
1. ionisation 2. sample viscosity
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ionisation
common in flames - xs energy causes ionisation of atoms - solution- add xs of readily ionised element
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what do we always want to be working within
the linear dynamic range
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Can we curvature be minimised
yes, but not avoided completely
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Min of how many standards required to make calibration plot
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