AX = F AS
[X] [S]
Chem 251 Exam 4 Fall 2005 NAME:
Questions on the exam are worth 10 points each unless otherwise noted. Show your setup for all calculations.
Peak Identification
1. Cytidine
2. Uridine
3. Xanthosine
4. Guanosine
5. Adenosine
1. Given the HPLC chromatogram above for a mixture of nucleosides, calculate the resolution between the Guanosine and Adenosine peaks using your best estimate of the required parameters from the chromatogram.
2. What is a theoretical plate? What are some factors that determine N?
3. What is gradient elution and why would you need to use it? Give two examples of types of gradients used in chromatography.
1 . Barbital(0.25 mg/ml)
2 . Phenobarbital(0.1 mg/ml)
3 . Talbutal(0.3 mg/ml)
4 . Amobarbital(0.25 mg/ml)
5 . Mephobarbital(0.1 mg/ml)
4. Given the HPLC chromatogram above for a mixture of barbiturates, calculate the number of theoretical plates based on the Amobarbital peak using your best estimate of the required parameters from the chromatogram.
5. Referring to the chromatogram at the top of the page, assuming that barbital is more polar than phenobarbital which is more polar than talbutal, etc, was this experiment run under normal or reverse phase conditions? (2 point question)
6. Short Answer: (2 points for each answer)
a. A resolution of ______is the minimum for baseline peak separation.
b. Which HETP is better, 0.5 mm or 1.0 mm?
c. The main purpose of chromatography is ______
d. The most common HPLC detector is:______
e. In liquid chromatography, the mobile / stationary phase is always liquid. (circle one).
7. (8 pt quest) Give the best match for the terms in the first list with the characteristics in the second:
____ normal phase chromatography
____ reverse phase chromatography
____ size exclusion chromatography
____ ion-exchange chromatography
A. One common stationary phase is DEAE
B. Mobile phase is more polar than stationary phase
C. Water in sample may cause interference because of its attraction to the stationary phase.
D. Smallest solute particles elute slowly.
8. A known mixture of compounds X and Y gave the following chromatographic results:
Compound / Concentration (M) / Peak Area (arbitrary units)X / 0.0842 / 423
Y / 0.0599 / 347
Next, a solution containing an unknown concentration of compound X was analyzed: To 10.0 mL of the unknown, 10.0 mL of a solution containing 0.146 M "Y" was added, and the mixture was diluted to 25.0 mL in a volumetric flask. This mixture yielded a chromatogram with two peaks with areas of 553 ("X") and 339 ("Y"). What is the concentration of "X" in the unknown?
9. Give the best match for the terms in the first list with the characteristics in the second: (8 pt quest)
____ TCD
____ ECD
____ FID
A. Detects the current change as the eluent passes through a flame.
B. Detects the current change as the eluent passes through a stream of high energy electrons.
C. Detects the current change due to the difference in heat conductance of mobile phase and analyte.
All of the above are: ______.
10 Give definitions of and describe the differences between WCOT, SCOT, and PLOT columns.
(6 pt quest)
11. Sketch a simple diagram of a GC. (6 pt quest)
12. A weak acid, HA, has a pKa of 6.5. If you are utilizing ion-exchange chromatography with an anion exchange resin, is pH 8.0 a good pH to facilitate this acid binding to the stationary phase? Why or why not? Hint: Which form predominates at pH 8.0?