final2005 - CHEM 3440 Final Examination Fall 2005 Duration:...

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CHEM 3440 Final Examination Fall 2005 Duration: 2 hours 1. (10 points) Chondrotinase is a protein which was analyzed by ESI FT ICR MS by Kelleher et al. in 1997. Some spectra are shown below. Mass here is reported in daltons (Da) = atomic mass unit (amu). (a) What do the acronyms “ESI FT ICR MS” stand for? (b) What is the mass of the protein at the peak at m/z = 1237.195? (c) The largest peak in the next cluster is at 1250.930. How is the molecule at this position related to that at 1237.195? (d) In the high resolution scan at the top, what is changing in the structure of the molecular ion fragments as we pass from one peak to the next? (e) At 1253.8, there is a smaller peak which is attributed to a small adduct attached to the protein. What approximately is the mass of this adduct?
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2. (12 points) Describe the following instrumental components. Outline the physical principles behind the operation of each one and specify any limitations to its operation. (a) A Geiger counter for the detection of x-radiation. (b) A quadrupole mass analyzer. (c) A visible white light source used in a Michelson Interferometer. (d) A pyroelectric detector for infrared radiation. 3. (6 points) Sucrose is enzymatically broken down into fructose and glucose by the enzyme invertase. sucrose invertase glucose + fructose The following procedure was used to determine the sucrose content of sweet potatoes. A 82.3 g sample of sweet potato was chopped into a juice. The juice was carefully collected (lots of washings) along with a buffer solution to form a final solution volume of 500.0 mL. Several 3.00 mL aliquots were taken and analyzed by a spectroscopic technique for glucose. Samples without any added enzyme determined the free glucose in the sample. Three trials of this gave the following concentrations: 212, 204, and 207 mg/dL. Invertase was added to three more aliquots and after 20 minutes, they were also analyzed for glucose, giving the following results: 462, 457, 454 mg/dL. (a) In units of mg/dL, what is the concentration of glucose arising from the decomposition of sucrose in sweet potato? (b) Given the molar mass of glucose (180.16 g/mol) and sucrose (342.2 g/mol), what is the percent sucrose (w/w%) in the sweet potato? 4. (6 points) At 323.75 nm, the molecule 4-acetic acid-7-methoxycoumarin has a molar absorptivity of 11,820 M -1 cm -1 . Our spectrometer can reliably measure transmittance between 1.00% and 90.0%. What is the range of concentration for this coumarin molecule that can be reliably measured in a 1.00 cm cell? 5. (6 points) During the development of a procedure for the fluorometric assay for the amino acid glycine, the attached spectra were acquired (see accompanying page). The glycine was reacted with a reagent, fluorescamine, which forms a fluorescent product with amines. In order to optimize the assay for sensitivity to glycine, to which wavelength should the excitation monochromator be tuned and to which wavelength should the emission monochromator be tuned? Will there be concerns about self-absorption? Why?
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6. (10 points) A calibration curve for the fluorescence detection of a certain sample was plotted from the following data
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This note was uploaded on 05/15/2010 for the course CHEM 3440 taught by Professor Danthomas during the Fall '06 term at University of Guelph.

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final2005 - CHEM 3440 Final Examination Fall 2005 Duration:...

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