Idea Transcript
DETERMINATION OF IRON (II), IRON (III) AND TOTAL IRON IN SOLUTION USING FIA AND AAS.
Objective:
1. To understand the principles and working characteristics of atomic absorption. 2. To determine the concentrations of iron (II), iron (III) and total iron in standards, unknown sample and tap water. 3. Compare and contrast the qualitation/quantitation capabilities of the atomic absorption spectroscopic method for Fe with that of FIA.
Text reference: Skoog, Holler, Nieman Principles of Instrumental Analysis, 5th edition, Saunders College Publishing, Fort Worth, TX 1997, Ch. 10. J. L. Burguera, M. Burguera, Analytica Chimica Acta, 161 (1984) pp. 375-379. J. Ruzicka, E. H. Hansen, Flow Injection Analysis, 2nd ed., 1988
The most common analysis method for the determining the concentration of metal ions in solution uses the atomic absorption spectrometer. In this method, solutions containing the metal ion of interest are aspirated into a nebulizer to divide the sample into a fine aerosol. The aerosol is then swept into a flame where it is desolvated. The metal-containing particles are then vaporized and atomized. The concentration of metal atoms in the flame is then determined by rationing the intensity of light incident on the flame with that exiting the flame at a wavelength specific for the metal of interest. A hollow cathode containing the metal of interest is an essential component for this experiment. The concentration of iron is often determined by atomic absorption spectroscopy, but sometimes it is important to know the concentrations of two different species of iron. Atomic absorption gives us only the total concentration of iron and no information on the oxidation state of the iron measure or the relations between two species of iron.
In this experiment we will utilize AAS to determine the total concentration of iron and FIA to measure the concentration of iron (II). Resultant of subtraction will give us the concentration of iron (III).
Reagents: 1. Acetic acid/sodium acetate (AASA) buffer: 0.2M acetic acid, 0.2 M sodium acetate. 2. Standard solution of iron(II): • Stock solution: 1000 ppm Fe(NH4)2(SO4)2 in AASA buffer • Working solutions: 2, 4, 6, 8, 10 ppm in AASA buffer 3. Standard solution of iron(III): • Stock solution: 1000 ppm Fe(NO3)3 in AASA buffer • Working solutions:2, 4, 6, 8, 10 ppm in AASA buffer 4. Standard solution of total iron: • Stock solutions: see 2, 3 • Working solutions: 2, 4, 6, 8, 10 ppm in AASA buffer 5. FIA carrier: 0.15 % (mass) 1,10-phenanthroline solution in AASA buffer
Procedure: 1. 2. 3. 4. 5. 6. 7. 8.
Prepare AASA buffer for solutions Prepare stock solutions Prepare working standards from stock solution. Measure iron (II) concentration of all standards that contain iron (II), unknown sample and tap water using FIA setup (see instructions for operation) Measure total iron concentrations of all standards, unknown sample and tap water using AAS by following the given instructions. Clean up all glassware and wash FIA instrument by running it with distilled water for 10 minutes. Shut down FIA and AAS instruments. Turn off gas and air supplies.
FIA settings: Carrier flow rate: 0,8 ml/min Sample volume: 150 µl Wavelength: 510 nm
Operating software WinFIA 3.0 for Windows
1. Open WinFIA 2. Select “Manual Control” 3. In dialog box ”Data readings” click “OFF” button 4. Select “Settings” 5. Click “Spectrometer Config” button 6. Switch off the light source and click “Dark Scan” button 7. Switch on the light source and click “Reference Scan” button 8. Choose absorbance mode (if not on) by pressing “A” button 9. Close “Spectrometer Configuration” 10. Click “Logon” button (make sure that logon was successful) 11. Select “Manual Control” 12. In dialog box ”Data readings” click “OFF” button 13. Select “Plots” 14. After injecting the sample click “Start” (on the right-hand side) and “Recording Off” buttons 15. Click button “Time Series” to view data collection in situ 16. When peak starts turn injection valve to the “load” position 17. When signal stabilizes at baseline make a new injection 18. After running all samples close “Data Acquisition” and click “Reset” and “Recording On” buttons 19. Select “Analysis “ 20. Click “Raw Data” button 21. Save data in folder “DATA” and exit Analyze data with Microsoft Excel. For operating AA-6200 see additional instructions.
Questions: 1. Compare and contrast iron (II) measurements from FIA and AAS. Include in your discussion following items: sensitivity, detection limits, selectivity, time per analysis, advantages.
2. Calculate the uncertainty in the final analyte concentration in unknown sample based on propagation of error analysis.
3. How could these measurements be made simultaneously? What makes it possible?
THINGS REQUIRED IN THE LAB REPORT.
1. Introduction (20 points) Theoretical principle instruments Apparatus Theoretical description of experiment 2. Experimental part (20 points) Description of the work done Results and calculations (concentrations of iron (II), iron (III) and total iron for unknown sample and tap water)
3. Discussion (40 points) Analysis of results (Discuss precision, accuracy and reliability of both instruments Error analysis (include possible error sources) Conclusions Summary 4. References (5 points)
5. Answers to the questions (15 points)