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:  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

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 Introduction (contd.)

Procedure  Objective: Determine concentration of an unknown solution.  Potassium Permanganate (KMnO 4 ) 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

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

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

Results – UV/VIS (contd.) Run Unknown Absorbance Calculated Concentration, g/L Average σ % CI0.104 Actual Concentration0.078 g/L ± g/L Table 1: UV/VIS unknown concentration analysis.

Results – AA Figure 3: AA Calibration Curve.

Results – AA (contd.) RunUnknown Concentration, g/L Average0.073 σ % CI0.019 Actual Concentration0.073 g/L ± g/L Table 2: AA unknown concentration analysis.

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

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

Error Analysis (contd.) 4. Operator Error: From comparison of previous users’ data and use of sample standard deviation 3.Dilution Error: Combine final concentration equation with error propagation equation

Error Analysis (contd.) Experiment Error TypeUV/VISAA Instrument Error, σ E E-05 Fit Error, σ E-05 Dilution Error, σ E-09 Operator Error, σ Total Error, σ E-05 σ With 95% CI Table 3: Summary of error analysis for both experiments.

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 g/L ± g/L (95% confidence)  AA provides a quick, easy, and relatively painless method for determining concentrations

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

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

Questions?

Schwedt, George. The Essential Guide to Analytical Chemistry. Wiley and Sons: Hoboken, NJ, Tissue, Brian M. “Atomic-Absorption Spectroscopy (AA).” 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, References