chm410h-d2008 - STUDENT NAME STUDENT NUMBER UNIVERSITY OF...

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Unformatted text preview: STUDENT NAME: STUDENT NUMBER: UNIVERSITY OF TORONTO Faculty of Arts and Science December 2008 Examination CHM 410H1F / ENV 1410H Analytical Environmental Chemistry W919» Duration — 3 hours Calculators are permitted. Total mark = 103 points over 11 questions Total 14 pages Tables 1 and 2 on page 2 for reference Marks for the test are allocated on a ‘mark—a-minute’ basis, so please judge the amount of detail required based on the number of marks allocated for each question. If I have seen further, it is only by standing on the shoulders of giants - Sir Isaac Newton 10f14 Table 1. Isotopic abundance and mass for select elements. Element Symbol Abundance (%) Isotopic mass Hydrogen H 99.985 1.007825 0.015 2.014102 0.00014 3.016030 Helium He mmmmmmm "mm" ~100 4.002603 98.90 12.000000 Carbon C _____________________________ m 1.10 13.003355 99.63 14.003074 Nitrogen N 0.37 15.000109 99.76 15.994915 Oxygen O 0.04 16.999131 0.20 17.888160 F 100 18.998403 Phosphorus P 100 30.973762 95.03 31.972072 Sulfur S 0.75 32.971459 4.22 33.967868 75.77 34.968853 Chlorine C1 24.33 36.965903 v 50.69 78.918336 Bromine Br 49.31 80.916289 Table 2. Performance characteristics of select mass spectrometers. Characteristic Quadrupole Ion trap Msaeiltlfilc Time of Flight FT-ICR M Ma“ Range < 4000 < 4000 15,000 Unlimited >104 - (In/z) .. ._ m - .... ... M ..................... .. Res°1Ving 4000 103—104 102—105 15,000 >106 .... . memwwm-w.WM-.MWW-WWW.--3-..“.-.“W-..”.-.-.....-.....W...W-_,WW Mass Accuracy 100 50—100 1-5 5—50 1-5 (ppm) 20f14 Question 1. You are involved as analytical support on an investigation into drug interactions between the anti-tuberculosis treatment isoniazid and the analgesics acetominophen and ibuprofen. You have been asked to isolate the compounds shown below from urine. Design an appropriate extraction scheme. (all analytes need to be in organic solvent at the end of the extraction) (6 points) 0 _ HN—O—OH N H0 NH2 Acetominophen Ibuprofen Isoniazid 3of14 Question 2. Explain the role of: (a) An instrumental or reagent blank in chemical analysis. (2 points) (b) A spike and recovery experiment. (2 points) (0) The flame in an F ID detector. (2 points) ((1) Columbic explosions in electrospray ionization. (2 points) (e) The dopant in atmospheric pressure photoionization. (2 points) (i) The collision cell in a triple quadrupole mass spectrometer. (2 points) 4of14 Question 3. The Van Deempter equation. (a) Draw Van Deemter plots for an LC column with 5 pm, 3 pm and 2 um particles. (2 points) a (cmlsec) (b) Using LC columns with 5 pm and 3 pm particles HPLC systems are generally run at flow rates of 0.2 to 0.5 mL/min. Using LC columns with 2 pm particles you can run flows of up to and beyond 1 mL/min. Explain with reference to the Van Deemter plots above. (Ignore issues related to high back pressure) (4 points) (c) Draw Van Deempter plots for a GC column using N2, He and H2 as the carrier gas. (2 points) it (cm/sec) 50fl4 ((1) Why are He or H2 typically used in GC applications? Explain with reference to the Van Deemter plots above. (4 points) Question 4. Certain compounds, such as phenol shown below, can be analyzed by either LC or GC. If you had a choice of either chromatographic technique, which would you choose and why? (5 points) OOH Phenol 6of14 Question 5. Triple quadrupole mass spectrometry is more sensitive than single quadrupole mass spectrometry. Similarly, fluorescence is more sensitive than absorption. Describe how both triple quadrupole mass spectrometry and fluorescence measurements increase detection sensitivity. (4 points) Question 6. 2,4-dichlor0phenoxyacetic acid (2,4-D) is a herbicide that is controlled in Quebec, but is still used in the rest of Canada and around the world. You have been hired to do the analytical work on a study of the environmental prevalence of 2-4- dichlorophenoxyacetic acid in water samples from around the world. The only internal standard available to you is 4-chlorophenoxyacetic acid. Describe an experimental approach that you would use to test whether 4-chlorophenoxyacetic acid is an appropriate internal standard for 2,4—dichlorophenoxyacetic acid analysis in your samples. (5 points) 0 O O\)J\OH o\)J\OH Cl/CECI Cl/O/ 2,4-dichlorophenoxyacetic acid 4-chlorophenoxyacetic acid Analyte of Interest Internal Standard 7of14 Question 7. The fluorinated phosphate shown below is used in paper food packaging. As you suspect humans will be exposed to this chemical you are interested in its biological fate. You decide to expose an animal (rat) to fluorinated phosphates and analyze the body fluids (blood and urine) for the parent compound and suspected metabolites. AS phosphatase enzymes are very common you believe the major fate of the fluorinated phosphate will be dephosphorylation into the corresponding fluorinated alcohol. There are many possible fates for this fluorinated alchohol. One in particular is sulfation into the corresponding fluorinated sulfate. F F FF FF F - F FWO\E _ dephosphorylatlon FWD” FFFFFFFFF \6’3 FFFFFF FFF _ Fluorinated alcohol Fluorinated phosphate CBF17PO3H l Sulfation F F FF FF F o FF FF FF FF F 3° Fluorinated sulfate CBF17SO3 (a) What extraction technique is appropriate to isolate the fluorinated phosphate and fluorinated sulfate from an aqueous biological fluid? Why? (3 points) (b) Would you analyze the fluorinated phosphate and fluorinated sulfate by LC or GC? Why? (3 points) (c) For the chosen chromatographic technique, what ionization source would you choose to couple to a mass spectrometer? Why? (3 points) 80f14 (d) How does this ionization source produce gas-phase ions? (5 points) (e) Which mass spectrometer(s) can distinguish between the most abundant mass of the fluorinated phosphate and the fluorinated sulfate? (4 points) (i) Aside from mass spectral evidence, What additional information could you use to identify the fluorinated phosphate and the fluorinated sulfate in your analysis? (3 points) 9of14 (g) You have confused your standards! You will never forget to label anything again! You decide to run the standards separately on a single quadrupole MS. Assign the resulting spectra to either the fluorinated phosphate or fluorinated sulfate, and explain your choice. (There is no fragmentation in these spectra) (4 points) W 5. YD E“ m E 5'3 2 4'33 455 are $551 45%)” 595' 51%: 525 5.35 5m: 55:: 21132.5er «3%) m a, 9. ea .4? fl 5 4e 2 241 O . 4-50 #50 4'50 489 QQO 580 51 a £25 530 540 55 '3 MEL-emu Question 8. MALDI ion source is often coupled to a time of flight MS, describe one reason why they work well together? (2 points) 10 ofl4 Question 9. You have been contacted by a biochemist that is interested in characterizing the size and function of a newly isolated microbial enzyme. The biochemist suspects the active site of the enzyme contains a Zinc cation and several tyrosine molecules. 0 .0 OH @ NH2 Tyrosine Zinc cation (a) As an initial characterization of size you decide to use size exclusion chromatography (SEC), a chromatographic technique that separates compounds based exclusively on size. You have access to any equipment in ANALEST, propose two detectors/instruments that would be capable of detecting the protein shown below. For each describe how the instrumentation works and why it would be capable of detecting the protein. (note: you do not have access to either LC- MS/MS used in the CHM 410/ 1410 labs). (10 points) llof14 (b) You decide to test the activity of the enzyme to specific substrates. To test the enzyme for esterase activity you place it in aqueous buffer with ethyl acetate. If the enzyme has esterase activity you expect to observe the reaction products acetic acid and ethanol. You would like to achieve a mass balance for this system, provide extraction and analysis method(s) to observe both the starting materials and products of this reaction. (6 points) 0 O A Esterase o/\ ' 0H + H°/\ ethyl acetate Acetic acid ethanol Question 10. If you need to analyze for the carboxylic acid shown below and the only analytical technique available to you is LC-UV, how could you do it? (4 points) 0 We” 12 ofl4 Question 11. YOu have been asked to develop a GC—MS method for bromobenzene. You plan to use single ion monitoring (SIM) due to its enhanced sensitivity. The electron impact (E1) spectrum for bromobenzene is shown below. EI spectra of bromobenzene 100 ns-Nw—isas Br 80 >\ :t.’ 8 CD 60 4.) 1—: <1) ,2 4.) 2 40 CD 05 20 0 25 50 75 100 125 150 175 m / z (a) Which mass—to-charge ratio(s) (m/z) would you monitor in your SIM method? Why? (2 points) (b) Which mass-to-charge ratio would you use for quantification? Why? (3 points) 13 of14 (c) Your collaborator has a GC-MS with chemical ionization. She shows you a negative chemical ionization (N CI) mass spectrum for bromobenzene containing only two peaks at 79 and 81 m/z. The LOD using BI is 1 ng/mL (ppb), while the LCD using NCI is improved to 0.01 ng/mL (ppb). a. What type of NCI ionization process produces these ions (79, 81 m/z) from bromobenzene. (1 point) b. Describe the mechanism of the ionization in (a) using chemical reactions. (2 points) 0. You have to advise your collaborator as to the most appropriate ionization technique for this analysis, describe the specific advantages and disadvantages of NCI as compared to E1 in this analysis. (4 points) END 14 ofl4 ...
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chm410h-d2008 - STUDENT NAME STUDENT NUMBER UNIVERSITY OF...

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