Your neighbor in the Chatham Apartments loves to play her music really loud, but you like it quiet when you study. You’ve been feuding much of the semester. Last week she brought you a nice card and some potpourri for your room, and you thought she wanted to apologize. However, you found an empty can of ethyl parathion in the dumpster this morning, and now you are beginning to worry that she is trying to poison you.

 

There are 6 questions of equal value; do any 5.  If you wish to complete a 5th question, I will count your top 5.  Each of the questions will be scored out of 20.

 

There are also 4 bonus points available.  See below on this page.

 

 

 

BONUS: up to 5 points (1 point for each reasonable test)

 

You have a container filled with either CO₂ or with N₂O.  Describe up to five chemical or instrumental tests that you could use to distinguish between these two room temperature gases.  N.B.  Tests that involve smelling, tasting or inhaling these gases will not count!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2a)       (8 points)         HPLC and GC are alike in many aspects, but they differ in many ways as well.  Focus on the most important difference illustrated in each the following:

 

1. Although direct injection is quite common in GC, it is never used in HPLC

 

 

1. GC-mass spec was commercially available long before LC-MS.

 

 

1. There is a much broader array of column choices for HPLC than there is for GC.

 

 

1. The shift from packed columns to capillary columns revolutionized GC, but this “breakthrough” was never copied in HPLC.

 

 

2b)       (12 points)       For each method, begin by identifying an analyte (or class of analytes) that takes full advantage of the benefits of this type of detector.  Your answer should be clear on what the primary advantage(s) of the detector is (are), and also describe a class of analytes that could not by detected by this method.

 

1. TCD for (GC)

 

1. ECD (for GC)

 

1. c) Mass Spec (for HPLC)

 

1. d) UV/ vis diode array (for HPLC)

 

 

 

3)          Your neighbor in the Chatham Apartments loves to play her music really loud, but you like it quiet when you study.  You’ve been feuding much of the semester.  Last week she brought you a nice card and some potpourri for your room, and you thought she wanted to apologize.  However, you found an empty can of ethyl parathion in the dumpster this morning, and now you are beginning to worry that she is trying to poison you.

 

4 points)          Draw ethyl parathion and provide its IUPAC name.  The “ChemDraw name” is also acceptable.

16 points)        Using any of the equipment we’ve studied to date, design an experimental protocol to determine how much, if any, ethyl parathion is in the potpourri.  Select the most appropriate form of instrumentation for the measurement, and explain your choice.

Describe any necessary sample collection, sample work-up, preparation of standards, proper instrument configuration (describe each component in the block diagram) and estimate the limit of detection you could expect. Be sure to cite your sources in this, and all your answers.

 

 

4) If you learn anything in Organic Chemistry, you learn that not all white powders are the same thing.  You’ve been hanging around in the lab after hours again, trying to make your own painkillers.  Now you have a white powder.

(15 points) For each of the following instrumental methods, describe (in no more than 2-3 sentences each) the sample preparation needed to prepare the white powder for analysis, and exactly what you could look for in the resultant data to differentiate between compounds 1 and 2 below.  Be sure that your sample prep choices do not conflict with the way you want to distinguish between your options.

(5 points) If you were a lawyer defending a client accused of possession of heroin based on the results of an HPLC analysis (with a single-wavelength detector), what questions might you ask in an effort to discredit the results?  Why?

a)      IR

b)     GC-MS

c)      HPLC-UV detection

d)     Fluorescence

e)      Mass Spectrometry (without GC or HPLC)

1) Codeine                                           2)  Heroin

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5)          In the interests of science, you convinced yourself it was necessary to set up and operate an illegal still.  You now have a clear colorless liquid, and two burning questions. You wish to know the “proof” of ethanol in the sample.  (proof = percent ethanol * 2; ex 40% ethanol = 80 proof)

 

In addition, you understand that if your distillation technique was bad and there was methanol in your distillate you could drink yourself blind, so you want to be sure it is methanol free.

 

In your lab you have GCs equipped with FID, TCD and ECD detectors.

 

(3 points)         Why is drinking MeOH hazardous to your eyesight?  (One sentence please; this is not biochem!)

 

(12 points)       Explain how you would configure the instrument for the experiment, including your choice of components, sample preparation, and how you would use the data to solve for the concentration of ethanol (and methanol, if present).  Include any necessary control or calibration experiments required by your method.

 

(5 points)         Simulate (draw) the data output that you would expect from the instrument configured as you above if your “moonshine” was actually 50% water, 40% ethanol and 10% methanol.  (draw chromatogram, but make sure it’s consistent to whatever detector you use)

 

 

 

 

 

 

6a) (4 points)   As part of a CHM lab, you have an aqueous solution buffered to pH 7.0 and containing the amino acids aspartic acid, arginine and glycine.  Draw the structures of these three amino acids at this pH, paying particular care to show the exact state of each potentially charged site.  (Hint: at pH 7, the backbone of every amino acid is zwitterionic.

 

 

6b) (8 points) Clearly explain the term “electroosmotic” flow as it relates to capillary electrophoresis.  As part of your answer, predict (and justify) the elution order of the three amino acids in the mixture above.

 

6c) (8 points)   Compare and contrast the operating principles of mass selection in TOF and quadrupole MS.

7) I have provided a PDF of a recent paper in food Chemistry (Food Chemistry 168 (2015) 1–6) that uses capillary electrophoresis to resolve and quantify low levels of biogenic amines from oysters.  Use this paper (and the specific quote below) as your starting point to answer the following questions.

 

The following line is excerpted from the introduction of this paper:  Therefore, aquatic products are among the fermented foods most commonly associated with BAs poisoning, and spermidine and putrescine are thought to indicate seafood quality.

 

• (2 points) Draw the chemical structures of these two compounds (spermidine and putrescine).

 

• (2 points)What are the LODs reported for each of these compounds in this paper.

 

• (4 points) In 2-3 sentences, explain the function of the detector in this method (note: we have not covered this in class yet.)

 

• (4 points) Predict the elution order of the two compounds using a phosphate buffer at pH 7.0. Explain your answer (or cite your source).

 

• (5 points) Provide citations for two other papers that measure / quantify putrescine levels using different techniques, and comment on the relative LODs.

 

• (3 points)Using the data in figure 4, determine which of the two compounds is the more sensitive probe of “product aging” in oysters.