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22 Cards in this Set
- Front
- Back
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While flame photometry measures light emission atomic absorption measures..
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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.
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what are the components of an atomic absorption instrument?
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1. Light source = hollow cathode lapm
2. Burnerhead w/ LONG head. 3. Monochromator 4. Photodetector 5. Readout |
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what is a hollow cathode lamp?
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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.
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how does the lite emit from a hollow cathode lamp?
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Supplied energy excites the gas; it bombards Ni (for eg) and the Ni emits lite upon returning to ground state.
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How is the burnerhead composed?
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with 3 zones in the flame:
1. Solids remain at the inner core 2. Where reaction occurs 3. Hydrocarbon products |
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why is the burnerhead long?
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to increase sensitivity
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what are the two types of burnerheads used?
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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. |
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what type of monochromator is used in atomic absorption?
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a Diffraction grating with narrow bandpass = 0.2nm!!
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What is the photodetector/readout in atomic absorption?
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Photodetector = PMT
Readout = meter or digital display |
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what are 2 possible types of instruments for atomic absptn?
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1. Single beam
2. Double beam |
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what are advantages/disadvantgs of a single beam?
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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.
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How is the "double-measurement" in single beam atomic absptn corrected?
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by using a ROTARY CHOPPER to convert lite from DC to AC, and a PMT designed to only recognize the ABSORBANCE of lite.
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Is the double beam atomic absorption photometer IN SPACE OR IN TIME?
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IN TIME - one detector.
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How does the double beam work?
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1. a rotating mirror is put between light source and flame
2. Incident light passes alternately through and past the flame. |
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Why use a double beam instrumnt?
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to correct temp fluctations in flame. Has a decreased warmup time, and the life is longer.
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what are advantages of atomic absorption?
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-increased sensitivity b/c of burner design
-increased specificity b/c of high quality monochromator. |
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what are 3 interferences associated with atomic absorption?
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1. Chemical
2. Ionization 3. Matrix |
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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 |
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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. |
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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. |
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what are the clinical applications of atomic absorption?
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1. Used for electrolytes that are hard to excite w/ flame photometry - Ca and Mg.
2. Low concentration ions. 3. Metal poisoning msmnts. |
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What is used in flameless atomic absorption?
what is the most common example? |
a chemical reaction and electric current.
-Graphite furnace atomic absorption. |
