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22 Cards in this Set

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  • Back
While flame photometry measures light emission atomic absorption measures..
absorption of lite! the solution is burned in a flame but remains in ground state; then a lite excites it. the amount of lite absorbed is pptl to concentration.
what are the components of an atomic absorption instrument?
1. Light source = hollow cathode lapm
2. Burnerhead w/ LONG head.
3. Monochromator
4. Photodetector
5. Readout
what is a hollow cathode lamp?
a light source that contains gas and a cathode that emits light of the same wavelength of the analyte - so you have to pick it to correspond to what you're measuring.
how does the lite emit from a hollow cathode lamp?
Supplied energy excites the gas; it bombards Ni (for eg) and the Ni emits lite upon returning to ground state.
How is the burnerhead composed?
with 3 zones in the flame:
1. Solids remain at the inner core
2. Where reaction occurs
3. Hydrocarbon products
why is the burnerhead long?
to increase sensitivity
what are the two types of burnerheads used?
1. Total consumption - not used; if sample is viscous, droplets cool flame/clog tip.
2. Premix - Lundgardh designed to increase sensitivity; uses the venturi effect.
what type of monochromator is used in atomic absorption?
a Diffraction grating with narrow bandpass = 0.2nm!!
What is the photodetector/readout in atomic absorption?
Photodetector = PMT
Readout = meter or digital display
what are 2 possible types of instruments for atomic absptn?
1. Single beam
2. Double beam
what are advantages/disadvantgs of a single beam?
simple design/relatively inexpensive; BUT, there's a mixture of excited and ground state electrons so emission is messy. 2 measurements are actually made - absorptn and emission! Also the cathode lamp has a short life.
How is the "double-measurement" in single beam atomic absptn corrected?
by using a ROTARY CHOPPER to convert lite from DC to AC, and a PMT designed to only recognize the ABSORBANCE of lite.
Is the double beam atomic absorption photometer IN SPACE OR IN TIME?
IN TIME - one detector.
How does the double beam work?
1. a rotating mirror is put between light source and flame
2. Incident light passes alternately through and past the flame.
Why use a double beam instrumnt?
to correct temp fluctations in flame. Has a decreased warmup time, and the life is longer.
what are advantages of atomic absorption?
-increased sensitivity b/c of burner design
-increased specificity b/c of high quality monochromator.
what are 3 interferences associated with atomic absorption?
1. Chemical
2. Ionization
3. Matrix
what are chemical interferences?

How does it affect results?
How is it corrected?
-test elements remain associated with anions in sample.
Decreases results
To correct add something that binds the anion. E.g., Lanthanum to bind phosphates and free up Ca/Mg
what is Ionization?

How does it affect results?
How is it corrected?
release of excited atoms to neverland instead of returning to ground state.
Results decreased.
Correct: reduce flame, or add another element that gets freed instead.
what is Matrix?

How does it affect results?
How is it corrected?
dissipation of flame energy by other salts, resulting in less dissociation of intended atom.
Decreases results
To correct, add protein.
what are the clinical applications of atomic absorption?
1. Used for electrolytes that are hard to excite w/ flame photometry - Ca and Mg.
2. Low concentration ions.
3. Metal poisoning msmnts.
What is used in flameless atomic absorption?

what is the most common example?
a chemical reaction and electric current.

-Graphite furnace atomic absorption.