Atomic spectroscopy

Discussion slides on atomic absorption/emission spectroscopy.

1. Principles, Instrumentation and Techniques in Atomic Absorption/Emission Spectroscopy JOSE G. INTANO, JR.

2. Overview Introduction to the Principles of Atomic Spectroscopy Instrumentation in Atomic Spectroscopy Selection of the Proper Atomic Spectroscopic Technique

3. Atomic Spectroscopy technique for determining the elemental composition of an analyte by its electromagnetic or mass spectrum atomic emission, atomic absorption, and atomic fluorescence understanding of the atom and the atomic process involved

4. Atomic Spectroscopy Figure 8.4. Three types of spectroscopy

5. Atomic Spectroscopy Different atomic spectroscopy systems HCL FLAME MONOCHROMATOR DETECTOR Figure 1. Simplified drawing of a Flame AA system . HCL GRAPHITE TUBE MONOCHROMATOR DETECTOR Figure 2. Simplified drawing of a Graphite Furnace AA system . PLASMA MONOCHROMATOR DETECTOR Figure 3 . Simplified drawing of a basic ICP system.

6. Atomic Spectroscopy Figure 6. Processes Occurring in Flame.

7. Atomic Spectroscopy

8. Atomic Spectroscopy Flame and Flameless Atomic Absorption Quantitation and Qualification of Atomic Spectroscopy Beer-Lambert’s Law is the basis for the quantificatitative determination A = abc A is the absorbance a is the absorption coefficient b is the length of the path light c is the concentration of the absorbing species

9. Atomic Spectroscopy Instruments for Atomic Spectroscopy Flame and Flameless Atomic Absorption Basic instrument components:

10. Atomic Spectroscopy Flame and Flameless Atomic Absorption Basic instrument components: Light source: hollow cathode lamp (HCL) Figure 2-4. Hollow cathode lamp process, where Ar + is a positively-charged Ar ion, M o is a sputtered, ground-state metal atom, M* is an excited-state metal atom, and λ is emitted radiation at a wavelength characteristic for the sputtered metal .

11. Atomic Spectroscopy Flame and Flameless Atomic Absorption Basic instrument components: Nebulizer and atomizer:

12. Atomic Spectroscopy Flame and Flameless Atomic Absorption Basic instrument components: Monochromator lenses m irrors gratings prisms .

13. Atomic Spectroscopy Flame and Flameless Atomic Absorption Basic instrument components: 3. Detector: Figure 1. Detectors used in atomic spectroscopy – traditional phototube, photomultiplier tube

14. Atomic Spectroscopy Cold Vapor Atomic Absorption (CVAA) Spectroscopy for Hg Free Hg atoms exist at room temperature, no requirement for heating Sample may contain Hg , Hg 2 2+ or Hg 2+ Reduction with a strong reducing agent (e.g. SnCl 2 or NaBH 4 )

15. Atomic Spectroscopy Hydride Generation Atomic Absorption (HGAA) Spectroscopy AsH 3 and SeH 3 generated by reaction samples containing As and Se with NaBH 4 Allso used for Pb , Sn, Bi, Sb, Te , Ge, Se determination

16. Atomic Spectroscopy Inductively Coupled Plasma Atomic Emission (ICP-OES) © 2010 by DBS

17. Atomic Spectroscopy Inductively Coupled Plasma Atomic Emission (ICP-OES) Sample is nebulized and entrained in the flow of plasma support gas (Ar) Source: http://www.cee.vt.edu/ewr/environmental/teach/smprimer/icpms/icpms.htm

18. Atomic Spectroscopy Inductively Coupled Plasma Atomic Emission (ICP-OES) Plasma torch inner tube contains the sample aerosol and Ar support gas Radio frequency generator produces a magnetic field which sets up an oscillating current in the ions and electrons of the support gas ( Ar ) Produces high temperatures (up to 10,000 K) Figure 2. Inductively coupled plasma torch

19. Atomic Spectroscopy Selection of the Proper Atomic Spectroscopic Techniques Important factors: Detection limit Working range Sample throughput Cost Interferences Ease of use Availability of proven methodology

20. Atomic Spectroscopy Comparison of Detection Limits and Working Range Low detection limit is essential for trace analysis Without low level capability – sample pre-concentration is required Figure 6. Typical detection limit ranges for the major atomic spectroscopy techniques.

21. Atomic Spectroscopy Comparison of Detection Limits and Working Range Ideal working range minimizes analytical effort and potential errors Figure 7. Typical analytical working ranges for the major atomic spectroscopy techniques.

22. Atomic Spectroscopy Comparison of Interferences and Other Considerations Interference 4 types: ( i ) spectral, (ii) chemical, (iii) ionization, (iv) physical/matrix

23. Atomic Spectroscopy Comparison of Interferences and Other Considerations SPECTRAL INTERFERENCES caused by radiation overlap of absorption line/emission line e. g. V line is 3082.11 A and Al is at 3082.15 A. Choose a different Al line at 3092.7 A. scattering of the radiation source due to matrix impurities e.g. Refractory oxides formed by Ti , Zr , and W due to atomization of high concentration solutions . Use a blank.

24. Atomic Spectroscopy Comparison of Interferences and Other Considerations BACKGROUND CORRECTION METHODS Continuum Deuterium Source Background Correction common background correction technique in FAAS significant at lower wavelength range (180nm-420nm) Figure 1. D2 Lamp Background Correction Schematic

25. Atomic Spectroscopy Comparison of Interferences and Other Considerations BACKGROUND CORRECTION METHODS Zeeman Background Correction Mainly used in GFAAS Figure 2. Zeeman Background Correction Schematic

26. Atomic Spectroscopy Comparison of Interferences and Other Considerations BACKGROUND CORRECTION METHODS Zeeman Background Correction Figure 3. Zeeman splitting of an atom in a magnetic field

27. Atomic Spectroscopy Comparison of Interferences and Other Considerations CHEMICAL INTERFERENCES REFRACTORY COMPOUND FORMATION c ompounds that cannot be broken down in flame e.g. Ca signal is depressed due to formation of Ca sulfate or Ca phosphate e.g. Mg signal is depressed in the presence of Al. Al forms heat stable compound with Mg .

28. Atomic Spectroscopy Comparison of Interferences and Other Considerations CHEMICAL INTERFERENCES SoLUTION FOR REFRACTORY COMPOUND FORMATION Use of Hotter flame Use of Releasing agents such as chlorides of La and Sr. Use of Protective agent such as EDTA and 8-Hydroxyquinolone

29. Atomic Spectroscopy Comparison of Interferences and Other Considerations IONIZATION INTERFERENCES affects Group 1 and 2 elements (Ba , Ca, Sr , Na, K) Solution: Use of Low Temperature Flame or Use of Ionization Buffer I onization buffer/suppressor/suppressant prevents analyte ionization e.g. Addition of a 0.1% KCl soln to blank, standard, and sample.

30. Atomic Spectroscopy Comparison of Interferences and Other Considerations MATRIX INTERFERENCES a physical interference and can either suppress or enhance absorbance signal of analyte . Causes : 1 . Differences in viscosity and surface tension. 2. Preparation in different solvents. 3. Measurement at different temperatures. 4 . Presence of organic species. 5. Different atomization rate in flame.

31. Atomic Spectroscopy Comparison of Interferences and Other Considerations Other Considerations Sample throughput, cost, ease of use, availability of proven methodology Single-element (FAAS and GFAA) vs. multi-element (ICP-OES/MS) Single: Change of lamp Run time ~1 min Multi: 10-40 elements per minute © 2010 by DBS

32. Atomic Spectroscopy Comparison of Interferences and Other Considerations Other Considerations Cost:

33. Atomic Spectroscopy Comparison of Interferences and Other Considerations Other Considerations ICP-OES and ICP-MS are multi-element techniques favored when there is a large number of samples and cost is not a concern

34. Atomic Spectroscopy Comparison of Interferences and Other Considerations Other Considerations ICP-OES has become the dominant instrument for routine analysis of metals Compared to FAAS: Lower interferences (due to higher temperatures) Spectra for most elements can be recorded simultaneously under the same conditions Higher temperature allows compounds (e.g. metal oxides) to be measured Determination of non metals (e.g. Cl, Br, I, S) © 2010 by DBS

35. Summary of Atomic Spectroscopy

36. References Csuros , M. and Csuros , C. (2002) Environmental Sampling and Analysis for Metals . CRC press, Boca Raton, Fl. Tatro , M.E. (2000) Optical Emission Inductively Coupled Plasma in Environmental Analysis. Encyclopedia of Analytical Chemistry , Edited by Meyers, R.A. John Wiley & Sons, West Sussex, UK. http:// delloyd.50megs.com/moreinfo/AAinterferences.html http://lab-training.com/2013/05/08/background-correction-in-atomic-absorption-spectroscopy / Thermo Elemental (2001). AAS , GFAAS, ICP or ICP-MS? Which technique should I use? An elementary overview of elemental analysis.