Atomic Spec Flashcards
Principle of atomic emission spectra
Atoms are thermally excited and electrons in outer shell gain energy and are elevated to a hugh electronic state. The excess of energy. Is lost by transition to the stable electronic ground state with emission of energy
What types of elements CAN be excited by AES
alkali metals and some alkaline earth metals
Main compeonets of instrumentation for AES
flame or plasma source
Monochromator / filter
Detector
3 factors that can interfere with AES
ionisation
Sample c
Viscosity
Anionic interference
How does ionisation interfere with AES
Atoms may lose an electron at hugh temps . This will reduce the emission.
Other readily ionised elements in the sample may effect the degree of ionisation
Solution - add excess of readily ionised elements eg k that will be ionised before the sample.
How does sample viscosity effect AES
organic substance in a sample can be increase or decrease the viscosity ehich effects the rate of sample transfer into the flame.
This effects the reading.
How does anionic interference effect AES
Anions form in volatile salts and reduce sample reading eg sukfate and phosphate ions.
Common name of elements in AES
Ca ba na li and k
How can yiu determine conc of atoms in samples in AES
Using a calibrating curve.
Solutions of known conc are aspirated and readings determined.
Build calibration curve conc v reading
Get equation of the line to determine conc of atoms in sample.
Principles of AAS
many heavier atoms eg zn can or be thermal,ly excited from the ground state to the excited state due to the Katie amounts of energy required.
These atoms are volatilised in a flame but not excited.
Radiation of a defined wavelength from a hollow cathode tube coated with the metal ti be analysed is passed through the flame.
The volatilised atoms absorb radiation either an energy corresponding to the difference between their ground and excited state.
The amount of energy absorbed relates directly ti the conc of metal atoms in the flame.
Why can AAS be used for a broader number of metals and atom s
There is a greater number of atoms in the ground state available for excitation than the number that become excited and emit energy in AES.
Four main components of instrumentation in AAS
Flame
Light source
Monochromator
Detector.
Interfering factors in AAS
Ionisation and sample viscosity
How does ionisation effect AAS
Species can become ionised in hot flame , effecting reading
Reduces no of e in ground state
