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UV/VIS Spectrometry And Atomic Absorption

UV/VIS Spectrometry And Atomic Absorption. By: Morgan Biehn. What’s Ahead…. Introduction to UV/VIS and AA Procedure Results Error Analysis Conclusions and Recommendations Q&A. Introduction. Ultraviolet/Visible (UV/VIS) Spectrometry:

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UV/VIS Spectrometry And Atomic Absorption

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  1. UV/VIS Spectrometry And Atomic Absorption By: Morgan Biehn

  2. What’s Ahead… • Introduction to UV/VIS and AA • Procedure • Results • Error Analysis • Conclusions and Recommendations • Q&A

  3. Introduction Ultraviolet/Visible (UV/VIS) Spectrometry: • A form of colorimetric analysis • Passes light through a cuvette containing solution • Referenced to a solution that absorbs no light (distilled water) • Beer-Lambert Law: A = αcl • In absence of α, use calibration curve

  4. Introduction (contd.) Atomic Absorption (AA) Spectrometry: • Samples must undergo desolvation and vaporization in a flame • When atoms absorb light, they transition to higher electronic energy levels • Concentration determined from amount of absorption • Flame AA can increase path length which increases absorption by Beer-Lambert Law

  5. Procedure • Objective: Determine concentration of an unknown solution. • Potassium Permanganate (KMnO4) solutions • 5 standards prepared with concentrations of 0.1, 0.09, 0.08, 0.07, and 0.06 g/L. Each standard tested twice • Perkin Elmer UV/VIS SP Spectrometer with 1 cm long cuvettes • Perkin Elmer AA spectrometer • Unknown solution tested five times for each method

  6. Results – UV/VIS Figure 1: UV/VIS spectra for five standards and unknown.

  7. Results – UV/VIS (contd.) Average absorption for unknown at 310 nm is 0.889 Figure 2: UV/VIS Calibration Curve.

  8. Results – UV/VIS (contd.) Table 1: UV/VIS unknown concentration analysis.

  9. Results – AA Figure 3: AA Calibration Curve.

  10. Results – AA (contd.) Table 2: AA unknown concentration analysis.

  11. Error Analysis Four types of error: 1. Instrument error 2. Fit error 3. Dilution error 4. Operator error

  12. Error Analysis (contd.) Instrument Error: Sample standard deviation Fit Error: Use calibration curve linear regression

  13. Error Analysis (contd.) • Dilution Error: Combine • final concentration • equation with error • propagation equation • Operator Error: From comparison of previous • users’ data and use of sample standard deviation

  14. Error Analysis (contd.) Table 3: Summary of error analysis for both experiments.

  15. Conclusions • UV/VIS and AA spectra were compared • Bad UV/VIS calibration curve produced large error • AA data provided smaller standard deviation than the UV/VIS • Unknown has concentration of 0.073 g/L ± 0.019 g/L (95% confidence) • AA provides a quick, easy, and relatively painless method for determining concentrations

  16. Recommendations • Monitor standards to reduce the risk of contamination • Store standards in a dark place • Try to conduct both experiments on the same day • Do as many tests as possible

  17. Where We’ve Been… • Background information on UV/VIS and AA experimental methods • Objective for this specific experiment and procedure to obtain objective • Discussion of Results • Discussion of error and which method produced more accurate results • Provided recommendations

  18. Questions?

  19. References Schwedt, George. The Essential Guide to Analytical Chemistry. Wiley and Sons: Hoboken, NJ, 1997. Tissue, Brian M. “Atomic-Absorption Spectroscopy (AA).” http://elchem.kaist.ac.kr/vt/chem.-ed/spec/atomic/aa.htm. Last updated 8/21/96. Walpole, Ronald E., Myers, Raymond H., Myers Sharon L. Probability and Statistics for Engineers and Scientists, 6th Edition. Prentice Hall: NJ, 1998.

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