4.8: TA Notes

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This page is directed toward laboratory teaching assistants, but is deliberately left open for students to read.

TA Notes

After completion of this module students will be able to:

Explain the principles of liquid-liquid partitioning.
Explain the effect of solvent polarity on retention times.
Explain the effects of isocratic and gradient methods on retention times and peak shape.
Interpret chromatographic data to identify components of a mixture and determine their concentration.

Pre-Semester Preparations

Do the following during the TA training and orientation week(s)

(See previous module)
Complete instrument training with Dr. Haas.
Perform the entire experiment as if you were a student.
Write and submit a report as if you were a student (this and the UV-vis part of the experiment).
Practice grading your and your partner's report using the grading rubric.

Pre-Lab Preparations

When you are on TA duty, arrive at least 20-30 minutes early to prepare and ready the following materials for students.

Check that all HPLC modules are powered on. The degasser (top unit) is the only one that should possibly be turned off at the button on the instrument.
Check solvent reservoirs and refill if they are less than half full.
Remind students to sign into lab
Check that the student's pre-lab is complete
Show students how to open the software and turn the instrument components on from the software.
Show students how to start a method running to equilibrate the column to the starting conditions of their first run. Be sure that the pressure is reasonable and the instrument is performing as expected. Otherwise, get help.

Helping your students

During the laboratory session, you are expected to be present and available for the entire 4.5 hours. Your job is to help students to complete the experiment safely and successfully, while upholding expectations and academic standards for the students.

In this particular laboratory session, you should be available to answer questions and troubleshoot any issues. Please discuss the following with them:

General principles of reverse phase chromatography.
How we predict relative retention of molecules based on their structure and the type of chromatography.
General expectations for isocratic vs gradient methods.
Selection of the appropriate wavelength for monitoring caffeine.

During data collection, check to be sure the report is giving peak integrations. If not, please show the students how to manually integrate the peaks and harvest their data electronically.

Remind students to use the control solution to validate their calibration. In this case, if the UV-vis calibration is valid, we expect the HPLC to also be validated. However, it this is not the case, please discuss with the instructor. In that case, we have confidence that the solutiosn were made correctly, and there must be another reason that the calibration has failed.

Shut down/ clean up

15 minutes prior to the end of the period, students should stop lab work and clean up. They are to leave the room in clean condition prior to the end of the period (17:55).

Remind students when it is time to clean up.
Remind students to save their samples!
Turn off the UV-vis
Remind students that all glassware should be returned to the storage locations.
Any samples that are stored should be labeled clearly with the student's name and section.
Remind students to sign out with the time they leave and get your signature.
Check the TA checklist for additional items to be completed.