Each element absorbs in only one particular wavelength (True/False)
False. One particular element has many different possible electronic transitions and therefore many specific wavelengths it absorbs
The ___ electrons undergo transitions when an atom absorbs light in AA
outer shell
What type of peaks result from atomic absorption?
Very well defined, sharp peaks
An atomic absorption spectrum is also referred to as a
line spectrum
A molecular absorption spectrum is also referred to as
A continuous, or band spectrum
It is a broad peak
Two types of line broadening
Doppler broadening
pressure broadening
This type of broadening can be minimized by adjusting the flow rate
Doppler broadening
This type of broadening is worse at higher temperatures
Pressure broadening
If you're getting unwanted molecular spectral lines, what can you do? What species are likely causing them?
Change wwavelength
Use a higher temperature fflame
Caused by OH-, CN-, other radicals
The line spectrum from the HCL is ____ than the atomic vapor spectra
Sharper, since the HCL is at a lower temperature and pressure than the flame
What element can't be used in a HCL?
Mercury ( it would pour out)
EDL
Electrodeless discharge lamp
An EDL uses the __ of a metal, which is ionized when an ___ is excited by ____
Salt
inert gas
RF field
A ___ has a higher light intensity (10-100x) but is less stable than ___
EDL
HCL
A chopper splits the light, which corrects for
Electronic noise
variations in lamp intensity
The process by which a sample is vaporized and decomposed to its atoms
Atomization
The formation of a fine suspension of liquid droplets
Nebulization
Only about ___ of the sample actually reaches the flame
5% or less
Name three types of flameless AA
Graphite ffurnace
Hydride generation
Cold vapor
Name two types of burners
Total consumption burner
laminar flow premix burner (what we've used)
Which type of flame tends to be noisier?
Nitrous oxide
Name three zones of the flame, which one is usually used for the AA light beam?
Primary combustion zone
interconal region, most common, hottest area
outer cone
Burner height has an affect on
Absorbance
As temperature increases, the number of atoms in ground state...
Decreases
As wavelength increases, atoms in ground state...
Decrease
Two ways to control flame temperature
Adjust air flow or fuel flow
switch fuel type or air type
GFAA
Graphite furnace atomic absorbance
Two ways in which matrix modifiers work
Cause the interferences to vaporize before the analyte
Keep the interferences tied up so that the analyte vaporizes first
Why can't you simple heat up your sample in the graphite furnace as fast as possible?
The sample will splatter, making threport ductilereport ductile
Graphite furnace is a good technique for which elements?
Metalloids (almost metals) such as As, Se, Te, also lead
HGAAS
Hydride generation atomic absorption spectrometry
Order the following from lowest to highest detection limit: ICP, Hydride Generation, Flame AA, Graphite Furnace
Hydride Generation (0.2 ppb)
Graphite Furnace (1 ppb)
ICP (40 ppb)
Flame AA (100 ppb)
Does HGAAS use a nebulizer?
No
Does the oxidation state of the metalloid matter for hydride generation?
Yes, it is crucial
What is dangerous about the waste from HGAAS?
It is strongy acidic
What moves the generated hydride gas into the optical cell?
An inert purge gas pushes it through
Is time from chemical reaction to the optical cell important in HGAAS?
Yes, shorter time is best and it must be consistent
Cold Vapor AA is useful for what element?
Mercury (Hg)
Why can mercury be analyzed with Cold Vapor AA?
It has a high vapor pressure
What are some advantages of Cold Vapor AA?
Fewer matrix interferences
Fewer spectral interferences
Improved detection limits
What chemical reactions must occur to prepare the mercury for analysis by Cold Vapor AA?
Oxidation (releases Hg from its compounds)
Reduction (converts all Hg ions to elemental Hg)
Why is a scrubber needed after Cold Vapor AA analysis?
Because the mercury vapors are toxic
What are 2 disadvantages of Cold Vapor AA?
Intensive sample prep
Hg contamination in the lab
If another element in your sample absorbs at the same wavelength as your analyte, what could you do?
Choose a different wavelength
Do sample prep before analysis to separate the interfering species
Which emits a broader band - deuterium lamp or the HCL?
Deuterium (its a molecule)
Name 2 limitations of deuterium correction
Udercorrection or overcorrection can occur
The HCL and D2 lamp must be aligned perfectly
The term for the splitting of electronic energy levels using a magnetic field so that several absorption lines are formed for each electronic transition.
Zeeman Effect
The Zeeman effect is mainly used for what AA technique?
Graphite Furnace
Name two types of chemical interferences
Formation of unwanted compounds
Ionization
Two ways to deal with interferences caused by unwanted molecules forming with your analyte
Releasing Agent - add something which reacts with the interferant more than your analyte does, thus freeing up the analyte
Protective (Masking) Agent - Forms a complex with the analyte preventing anything else from getting to it
Which type of flame is ionization more of a problem with?
Nitrous
What can you do if you're experiencing ionization interferences?
Add an ionization suppressor such as K
EIE
Easily Ionizable Element
What element may cause ionization problems (by being greedy for electrons)?
Aluminum
Mercury typically has a ___ hold time than other elements. Why?
Shorter (Hg has a 26 day hold time instead of 6 months)
It's more volatile
Author
saitclt
ID
186965
Card Set
AA Review
Description
Cynthia's review of Atomic Absorption Terms and major concepts
