Atomic Absorption Spectroscopy (AAS) Flashcards
what is an atom made up of?
Of a nucleus surrounded by electrons
What is the ground state in the normal orbital configuration for an atom?
it is the lowest energy, most stable electronic configuration of an atom
What happend if the energy of the right amgnitude is applied to an atom?
The energy will be absorbed by the atom, and an outer electron will be promoted to a less stable configuration
what’s the name of the less stable configuration state?
it is the excited state
What happend to the atom at the excited state?
the atom will immediately and spontaneously return to its ground state configuration
What’s the results of the return of the atome to its ground state?
the energy intially absorbed in the excitation process will be emitted.
What’s the different between excitation and decay?
Draw the difference
the excitation is forced by suppying energy, whereby the decay proces involve the emission of light, occurs spontaneously
how is the wavelength related to the electronic transition?
the wavelength of the emitted radiant energy is directly related to the eletronic transition
AA emission is?
On measured the emitted light at the wavelength of the elment to be determined
How is the emission intensity correlated to the number of atoms?
the intensity at the wavelength will be grater as the number of atoms of the analyte element increase
Define atomic absorbtion
When the right wavelength impinges on a free, ground state atom, the atom aborb the light at it enters an excited state
What’s the relation between the quantity of interest and the amount of light absorbed?
the quantity of interest is the amount of light which is absorbed as the light passes through a cloud of atoms.
Describe the atomic absorption process
- A light (resonance wavelength) of intialy intensity (Io) is forced on th e flame cell containing ground state atoms.
- the detector measred the reduced light intensity (I)
How does the intial light intensity decreases?
it decrease by an amount determined by the atom concentration in the flame cell
Define transmittance (T)
it is the ratio of the final intensity to the inital intensity (T= I/Io)
What’s the percent transmission
%T= 100* I/Io
relation between the percent absorption and percent transmission
the percent absorption is the complemnt of percent transmission
%A= 100- %T
How is the absorbance define absorbance
A= log(Io/I)
what is the absorbance?
it is the used for characterzing light absorption in AAS
Why do we used the absorbance?
it’s floows a linear relationship with concentration
Formal for the Beer’s law
A=abc
a: absortion coefficient
b: length
C: concentration
What’s the meaning of Beer’s law equation?
it’s tells us that the absornace is diretly proportional to the concentration of the absorbing species.
What are the component of an AAS?
Draw it
light soure, sample cell, specific light measurement (Monochromator, detector, electronics and readout)
What’s the widely used light source
Hollow cathode lamp
Electrodeless discharge lamp
What’s the used of a monochromator?
it is used to disperse the varous wavelengths of light which are emitted from the source and to isolte the particular line (wavelength) of interest
why is a narrow light absortion important?
it is of importance to use a line source which emits the specific wavelngths which can be absorbed by the atom.
Narrow line sources provide high sensitivity
Describe the process of an AAS
1.Process
The element of interest is dissolve in a solvent.
The liquid is drawn into the nebulizer and mixed with oxidanet (air) and fule (acetylene), where it gets disperes into small droplets (Aerosol)
Aerosol enters in the flame, where the liquid is evaporated
Describe the process of an AAS
2 .Process
Aerosol enters in the flame, where the liquid is evaporated, remaining solid is vaporized
Describe the process of an AAS
3 .Process
the solid sampe is decomposed into atoms
What the flams temperature and by what it is created?
it is created by the air-acetylene, 2400-2700 K
Describe the process in the HCL
the applied voltage in the HCL ionizes the gas which fills the lamp
positive ions are accelarated toward the cathode.the catiosn strike the cathode, creating energy which takes the matal atoms frin the cathode into the gas phase. Due to collisions in the gase ohase, the atoms are excited of the specific elemnt which emit high-energy protons with the frequency that the analyte inside the flame needs to absorb
Why do we need to used a specific light source and not a normal light?
According to the Beer’s law is it important to have a line relation between the absorbtion and the concentration of the element.
the atom can only absorbt a tiny fraction of all of the light of the monochromater, producing a very non-linar response.
What is important in the HCL
in the HCL, the lamp content the same element a that which is to be determined. Therefore, the wevelength emission profile gives the same engery and shape as the atom in the sample. Therefore, on can directly match the wavelength from the light as beig absorbt by the sample
What’S the main different between atoms and molecules
Atoms can only aborbt energy, but they can’t rotate or vibrat to gain energy. Therefore, atom have a very narrow absorption lines
What’s the disadvantage of this method?
one needs a different lamp for each type of metal which is to be determined
what is important in the atoms to get in th excited state?
they need to absorbt radiation in the same frequency of their energetic level between the ground and the excited state
Importance of Ascorbic acid and the reaction
it is an antioxidant, which reduces Fe(3+) to Fe(2+) in the human body
Why is the lambert-beer law limited in the AAS
it is due to the thickness of the flame, which cannot be dtermined exactly
What is ppm
ppm means part per million which is equal to mg/l
Why do we used ppm instead of the %
what is the visualization of the ppm?
the numerical value will be extremely samll in a number of decimal places if the % is used
one inch in 16 miles
what is the results of a prologe exposure of zinc in the body?
it can reduce immune function and lower the high density of lipoprotein (HDL)
What is a Milli-Q water
it is an ultrapure water, deionized through the filter to remove particles. it is more pure than distilled water
