Atomic spectroscopy ch 20
-
Upload
vanessawhitehawk -
Category
Technology
-
view
165 -
download
1
Transcript of Atomic spectroscopy ch 20
![Page 1: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/1.jpg)
Atomic Spectroscopy (Chapter 21)
Used for qualitative and quantitative determinationsWidely used in industrial settingsDetection limits: ppm, ppb
Convert sample to atomsDetermine atom conc. by measuring A or IA = kC I=kC
Three classes:absorptionemissionfluorescence
![Page 2: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/2.jpg)
Atomic Spectroscopy (Chapter 21)
GS
ES
GS
ES
thermal
AAS AES
![Page 3: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/3.jpg)
![Page 4: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/4.jpg)
Atomic Spectroscopy (Chapter 21)
Step 1: Atomization
Volatilize, decomp. to form atomic gas
1. Convert solution to a mist2. Carry into source
CaCl2(soln) CaCl2(gas) Ca0(gas) + 2Cl0(gas)
Excitation: Ca0(gas) Ca*
(gas)
Emission: Ca*(gas) Ca0
(gas)
AA: measure ground state AE: measure excited state
3. Evaporate solvent4. Vaporize5. Decompose to atoms
![Page 5: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/5.jpg)
Why are spectraso narrow?
![Page 6: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/6.jpg)
Atomic Spectroscopy (Chapter 21)
Atomization Sources1. Flame (AA, AE)2. Furnace (AA)3. Plasma (AE)
A. Flamepneumatic nebulizerburnerflame temperature is impt (1700 – 3100 C)
![Page 7: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/7.jpg)
![Page 8: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/8.jpg)
![Page 9: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/9.jpg)
![Page 10: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/10.jpg)
T ~ 2500 KSmaller volume (L)
Greater sensitivityLonger residence timesLess reproducible, more complicated
why?
![Page 11: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/11.jpg)
![Page 12: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/12.jpg)
Very high Temperature (6000 - 10,000K)Large ES populationReduced interference
C. Plasma
ICP
why?
![Page 13: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/13.jpg)
Atomic Spectroscopy (Chapter 21)
Temperaturevery importantdegree at which sample breaks downdetermine the percent of atoms in GS, ES, or ionized
N* / No = g* / go exp (-E/kT)
If T = 2500 K ( = 500 nm) N*/No = 10-5
If T = 6000 K N*/No = 10-2
AE: I depends of ES populationchange T by 10 K, change N* by 4%
AA: A depends of GS populationChange T by 10K, little change in N
![Page 14: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/14.jpg)
Instrumentation
SourceSample cellMonochromatorDetector
Beers Law: “monochromatic”molecule spectra – much broader than bandwidthatomic spectra – much narrower than bandwidth
(0.001 – 0.01 nm)
![Page 15: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/15.jpg)
1. Need a special source: Hollow cathode lampelement specific
why?
![Page 16: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/16.jpg)
2. Background Subtraction Methodsremove flame signal from atom
![Page 17: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/17.jpg)
Interferencesspectralchemicalionization
Spectraoverlap of analyte signal with other signals (molec – element); chose another , change T
Chemicalchemical reactions decrease conc of of analyteexample: Ca2+ in presence of SO4
2-
add a releasing agent (EDTA) or change temp
Ionizationionization of atoms decrease conc. of neutral atomsex. Kg K+ + 1e-
Add an ionization supressor (Csg Cs+ + e-)
![Page 18: Atomic spectroscopy ch 20](https://reader036.fdocuments.us/reader036/viewer/2022062513/55643138d8b42a06138b4cb5/html5/thumbnails/18.jpg)
Detection Limits
Depends on element and method
Element ICP Flame E Flame A FurnaceCa 0.02 0.1 1 0.02Fe 0.3 30 5 0.005Na 0.20 0.1 2 0.0002
units: ng/mL
What is better, big number or small number?