仪器分析Chapter 4

Integral Absorption Formula
By atomic theory
∫ k dv =
v
πe 2
mc
fN 0
(4.1)
By Line Shape Function ( the Nature distribute )
∫
+∞
0
k v dv =
1 2
π
ln 2
k 0 ∆v D
(4.2)
The Peak Absorption Coefficient k0 is:
The ‘‘characteristic concentration’’ ( sometimes called ‘‘sensitivity’’) is a convention for defining the magnitude of the absorbance signal which will be produced by a given concentration of analyte. For flame atomic absorption, this term is expressed as the concentration of an element in milligrams per liter ( mg/L ) required to produce a 1% absorption ( 0.0044 absorbance ) signal.
Fig 4-14
3. Atomizer for AAS (Pre-Mix Burner System)
Fig 4-19 Tree Type Burner Head for different Type Flame
4. Control of Analytical Interferences
k0 =
2 ∆vD
ln 2 πe 2 π mc
fN0
(4.3)
⑵ Peak Absorption Theory
by Lambert-Beer’s Law:
Iv = I e
∆v 0
0 − kvl v
∆v 0 − kvl v
(4.4)
P = ∫ I v dv = ∫ I e
0
dv
(4.5)
P0 = ∫ I dv
1.
The Atomic Absorption Process
Fig4-2 Grotrian diagrams for K
Fig 4-3Grotrian diagrams for Na
2. Theoretical Concepts
⑴Integral Formula of AAS Fig 4-4 Typical Shape of A Atomic Absorption line
∆v 0 − kv l v 0 ∆v 0 v 0
− k0l ∆v 0 v 0 ∆v 0 v 0
A = 0 . 4343
2 ∆vD
ln 2 π e 2 π mc
flN 0 = KN 0
(4.9)
3. Quantitative Analysis
A = KC
(4.10)
4. Characteristic Concentration
0 Vs
Vx
3 4
Cs
2Vs 3Vs
Background Interference
AD2=Ab, AHCL= Aa+ Ab Aa = AHCL- AD2
(4.13) (4.14) (4.15)
4.3. Graphite Furnace Atomic Absorption
1. Graphite furnace atomizer components 2. The Graphite Furnace Power Supply and Programmer 3. Quantitative analysis GFAAS 4. Effect of Matrix on Height and Area
Chapter 4
Atomic Absorption 4.1. Theoretical Concepts Spectroscopy
4.2. Atomic Absorption Instrumentation 4.3. Graphite Furnace Atomic Absorpcal Interferences
0 0 v
∆v
(4.6)
The Absorbance is:
P A = − lg P0 = − lg
∆v 0 − k l ∫0 I v e v dv ∆v 0 ∫0 I v dv
(4.7)
When ∆va>> ∆ve, then kv≈k0,
e ∫ I dv ∫ I e dv A = − lg ≈ − lg = 0.4343k0l (4.8) ∫ I dv ∫ I dv
(4.12)
4.2. Atomic Absorption Instrumentation
1. Photometers for AAS
A New Type Photometer for AAS
2. line source (Hollow Cathode Lamp )
Fig 4-13
Hollow Cathode Lamp Emission Process
THGA graphite tube
Fig 4-27
2. The Graphite Furnace Power Supply and Programmer
A Graphite Furnace Temperature Program 1) Drying 2) Pyrolysis 3) Cool Down(optional) 4) Atomization 5) Clean Out 6) Cool Down
Ionization Interference Matrix Interference Chemical Interference Background Interference
Ionization Interference
Matrix Interference
Chemical Interference
4.1. Theoretical Concepts
1. The Atomic Absorption Process 2. Theoretical Concepts 3. Quantitative Analysis 4. Characteristic Concentration 5. Detection Limits
(4.11)
5. Detection Limit
Having obtained the data, make the calculation as follows: 1. Average the two blank readings taken immediately before and after each standard and subtract from the standard reading. 2. Calculate the mean and standard deviation for the set of corrected high-standard readings. Do the same for the set of corrected low standard readings. 3. If the ratio of the means does not correspond to the ratio of the concentration prepared to within statistical error, reject the data. 4. If the data pass the ratio-of-the-means test, calculate the concentration detection limit as follows:
The Method Of Standard Additions
No. 1 2
Sample Added ml Standard Added ml Concentr.o Last f standard Concentriatio mg/L n mg/L
Vx VL Vx+CsVs VL Vx+2CsVs VL Vx+3CsVs VL
1. Graphite furnace atomizer components
The Graphite Furnace Atomizer A basic graphite furnace atomizer is comprised of the following components: • graphite tube • electrical contacts • enclosed water cooled housing • inert purge gas controls