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Atomic Absorption and Atomic Fluorescence Spectrometry Section A. By Matt Boyd, James Joseph, Jon Blizzard, Jackie Freebery, Hunter Bodle. Atomization Techniques. AAS and AFS Two techniques Flame Atomization Electrothermal Atomization. Flame Atomization .
By Matt Boyd, James Joseph, Jon Blizzard, Jackie Freebery, Hunter Bodle
Section 9A: Sample Atomization Technique
By Rachel Conroy
Shown is the cross-sectional view of a graphite furnace atomizer. The L’vov platform and its position in the graphite furnace.
These signals are then converted into electrical responses
A high pass RC filter (section 2B-5) can be used to remove unadjusted signals
Megan Seeger, Andrea Lando, Joe Bailey, and Sarah Duncan
MO M + O
The M is the analyte atom and the OH is the hydroxyl radical.
NaCl Na +Cl
Adding HCL decreases Na concentration thereby lowering line intensity.
VOx V + Ox
AlOx Al +Ox
TiOX Ti + Ox
M M+ + e-
K= [M+][e- ]/ [M]
Degree of Ionization of metals at flame temps. Table 9-2 pg. 246
Atomic Absorption Analytical Techniques
1. Flame Spectroscopic Methods
Common problem: most are insoluble in aqueous solutions so preliminary treatment to the sample is required
Decomposition of material
Con: risk losing the analyte by volatilization or as particulates in smoke
Con: can cause chemical and spectral interferences or can cause the analyte to appear as in impurity in the solution
Common Decomp. Methods
1. Treatment with hot mineral acids
2. Oxidation with liquid reagents (sulfuric, nitric, or perchloric acids: wet ashing)
3. Combustion in an oxygen bomb (or other closed container)
4. Ashing at high temperatures
5. High temperature fusion with reagents ( boric oxide, sodium carbonate, sodium peroxide, and potassium pyrosulfate)
1. Liquid Samples: blood, petroleum products, and organic solvents.
* liquid solvents can be pipetted directly into the furnace for ashing and atomization.
2. Solid Samples: plant leaves, animal tissues, and inorganic substances.
* solids can be weighed directly into a cup-type atomizer or into specific containers for introduction into a tube type furnace.
Low Molecular-weight organic solvents:
Why Organic Solvents?
Leaner fuel-oxidant ratios must be used to offset the presence of any added organic material
ex: Methyl isobutyl ketone
Common Chelating Agents-
Should Follow Beer’s Law:
A: absorption (L/ g●cm)
b: path length through medium
Should cover range of concentration found in the sample
1 standard solution should be measured after each time an analysis is performed. Using 2 standards that bracket the analyte concentration would be more efficient in identifying any uncontrolled variables that result from atomization and absorbance measurements
Table 9-3 shows Detection Limits
Columns 2 & 3 present detection limits for a number of common elements by flame and electrothermal atomic absorption
Useful and convenient for quantitative determination of many elements
Not used as often as atomic emission and atomic absorption
Useful for determining elements that form vapors and hydrides- Pb, Hg, Cd, Zn
Fluorescence instruments are generally harder to maintain and thus more expensive
Sample container is usually a flame or electrothermal atomization cell, glow discharge, or an inductively coupled plasma
Continuum source is ideal
Hollow cathode lamps were used frequently but now EDLs (electrodeless discharge lamps) are more common
EDLs have greater intensity than hollow cathode lamps
Lasers are good sources despite increased costs and operational intricacies