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CHEM 213 Instrumental Analysis

CHEM 213 Instrumental Analysis. Lab Lecture – Fe and Extraction. 3 + Fe 2+ Fe(bipy) 3 2+. red. Bipyridyl (bipy). Determination of Trace Iron (LM, p14-22). Chem 102 – used Crystal field theory to explain colour of coordination complexes

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CHEM 213 Instrumental Analysis

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  1. CHEM 213Instrumental Analysis Lab Lecture – Fe and Extraction

  2. 3 + Fe2+ Fe(bipy)32+ red Bipyridyl (bipy) Determination of Trace Iron (LM, p14-22) Chem 102 – used Crystal field theory to explain colour of coordination complexes Chem 213 – use intensity of colour to determine concentration of metal ion Spectrophotometry – any method using light to measure chemical composition

  3. Fe: Concentration to Colour Intensity of colour = Absorbance (A) Measure absorbance of soln to determine the iron concentration. P/P0 %T A 1 100 0 0.1 10 1 0.01 1 2 Transmitted Transmittance (T) = P/Po Absorbance A = -log(T) = abc a = absorptivity b = pathlength c = concentration

  4. Mode Readout Readout On/Off On/Off Zero control Spec 20D+ pg 21 Genesys 20 pg 21 Sample comp. Spectrophotometer (Text p410, LM p19-21)

  5. Insert 2nd tube in spec • Rotate tube to get T=90% • Mark tube with line • Put on alignment line Spectrophotometer (Text p410, LM p19-21) Record spectrometer number • Sample cell matching LM p 19 (1 hour) • Need 8 test tubes with the same pathlength (b) • prepare dilute amaranth dye soln • Set wavelength to 510 nm • Insert test tube in sample compartment • Adjust trans/absorb control to 90% • Repeat until you have 8 • matched tubes

  6. 3 + Fe2+ Fe(bipy)32+ Bipyridyl (bipy) 2. xs + Fe2+ Fe(bipy)32+ Determination of Trace Iron (LM, p14-22) • Reduce any Fe(III) to Fe(II) so all iron is in the Fe(II) state, because only Fe(II) forms coloured complex red + xs NH2OH  Fe2+ hydroxylamine reducing agent 1. Fe3+acidic 3. Adjust pH to ~ 5 by adding sodium acetate

  7. Determination of Trace Iron(LM, p14-22) Measure absorption spectrum of the complex to determine the wavelength of max. absorbance. Absorbance spectrum – graph of absorbance of light vs. wavelength A = abc Measure A for most conc standard from 640 to 400 nm at 20 nm intervals. The 0 %T (20D Only) and the 100 %T (A = 0) settings must be reset for each new wavelength.

  8. Determination of Trace Iron (LM, p14-22) Why is 100 %T (A = 0) reset at each wavelength? Light intensity (Po) varies with wavelength) A is max Best sensitivity

  9. Prepare Calibration Curve Standards = pipet 5, 10, 15 & 20 mL Fe3+ into flasks Blank = soln with all of the reagents but no analyte [Fe3+]=0 Zero (set A =0) instrument using blank Measure absorbance of all standards and samples Re-zero Take second absorbance reading for all stds and samples

  10. Prepare Calibration Curve standards Asample Blank Csample

  11. Calibration Curves LM, Appendix A

  12. Calibration Curves • Calibration Curve – graph of instrument response vs. conc of analyte • when response for sample is measured, its conc is determined by interpolating from the graph • - blank value should be part of the calibration curve, i.e. signal for [C] = 0.0 • -standards must cover the complete range of expected unknowns • - plot signal on the Y axis and conc on the X axis. • Normally response is linear • or with math transformation can be made linear • Signal = m(conc) + b • m = slope b = intercept

  13. Drawing a Calibration Curve Manually on graph paper

  14. Manual Graphing of Calibration Curve Useful for spotting:

  15. Manual Graphing of Calibration Curve Useful for spotting: outliers

  16. Manual Graphing of Calibration Curve Useful for spotting: outliers curvature

  17. Manual Graphing of Calibration Curve Manually on graph paper - best for spotting outliers, curvature, etc. - disgard outliers Calculate least squares line Mathematically calculate line using least squares fits data to y = mx + b ? determines m and b determines error in m and b? allows accurate calculation of sample conc

  18. Solvent extraction Determination of Dextromethorphan in Cough Syrup Preservatives Flavouring Colouring Expectorant Glyceryl guaiacolate Antihistamines Chloropheniramine maleate Diphenyhydramine HCl Decongestants Phenylephrine HCl Analgesics Acetaminophen Dextromethorphan cough suppressant toluene water

  19. (DMH+ BTB-)org yellow toluene water + (DMH+BTB-) Dextromethorphan DMH+ Bromothymol blue BTB- B. Solvent Extraction System  [BTB-]org = Absorbance @ 400 nm Colour  [DMH+]aq Calibration curve: (absorbance-blank) vs. [DMH+]aq Ion-association Extraction ion pair xs

  20. First week solution preparation (pg 50) Do NOT add BTB Do NOT prep sample

  21. d) Fluted filter paper – allows liquid to pass through quickly b) Mohr pipet – use like a buret

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