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: Use online resources to find expected values for \(\lambda_{max}\) for the dyes Follow instructions to operate a UV-visible spectrophotometer Apply chemical theories (particle in a box) to explain experimental observations Use programing skills and computational software (MatLab) to analyze data Practice recording observations in an electronic laboratory notebook (ELN) Apply knowledge of chemical theories and data to describe and discuss results Pre-Semester Preparations Do the following during the TA training week(s) Check that the materials listed below are available and sufficient for all students to use them. All items are in the prep room on the shelves and in the refrigerator/freezer. If they are running low, please create more or inform the instructor. Each group of 3-4 students will need the following: Set of 4 Dye solutions : One set of the dye solutions Methanol reagent : One small bottle of reagent methanol for diluting the dye solutions. At least five glass Pasteur pipettes: one for "clean" methanol, and one for each dye solution. Bulbs : at least three bulbs to be used by multiple students preparing solutions. Set of 4 glass cuvettes: One cuvette for each dye solution Cuvette rack: One is required, two racks is ideal. **Teach students to always keep cuvettes in a rack or instrument cell holder, never directly on the bench. Methanol wash bottles : Be sure that there is one full methanol wash bottle available for each group. This is for rinsing cuvettes. Lab wipes (ie Kimwipes) for wiping cuvettes. Paper towel mat to catch spills. Additional paper towels are at sink areas. 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. 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 materials listed above for students. Most of the set-up can be done ahead of time, but dye solutions should be kept cold when not in use. Take dye solutions out of freezer and place them at student stations. Check that dye solution colors are as expected (see Figure \(\PageIndex{2}\)). Dye #1 : 1,1’-diethyl-2,2’-cyanine iodide is pinkish-orange. Dye #2 : 1,1’-diethyl-2,2’-carbocyanine chloride is bright blue (not purple at all!) Dye #3 : 1,1’-diethyl-2,2’-dicarbocyanine iodide is dark turquoise . Dye #4 : 1,1’-diethyl-4-4’-carbocyanine iodide is dark blue (not yellow/green/brown color) At the UV-vis instrument and computer: Turn on the UV-vis if you'd like to allow it to warm up. Create a file folder for that day's section in the course directory on the computer hard drive. Put the most recent version of the ELN on the UV-vis computer you will use. 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, please provide guidance and instruction on the following: Creating the solutions for analysis : Students will put a few drops of the concentrated dye solutions into the cuvette and dilute with methanol. Please have an idea of what the solutions should "look like" (ie how dark/concentrated the should they be so that students can collect usable spectra). And, please make sure students are filling their cuvette about 3/4 full (not too full that it spills in the spectrometer, but full enough so that the light beam goes through the solution). Using the spectrometer : Be ready to step in if the students ask for help while validating the instrument and taking the spectrum. Be able to answer questions like "do I need to put a blank cuvette in the back"? "Do I need to take a baseline"? "Why does my spectrum look all noisy at Abs = 3? "Why do we need glass cuvettes - can I use quartz?" Annotating spectra: Show students how to add their wavelengths and label the Dyes on the spectrum through the annotation tool. Saving data: Please direct students to the folder in the course directory and instruct them to save their data to that folder using the format "YYYMMDD_filename_comments" Filling out their ELN: Be aware of what information the students should put in their ELN and guide them appropraitely. If they are moving on to the next step without recording the data, please remind them to do so. But, please let students do it themselves. Taking turns: Please help students to take turns controlling the instrument. Each student should be allowed to collect and annotate at least one spectrum. Using the custom "dye" script in MatLab: Be familiar with the script and how it is used, and guide students through the steps as necessary. Encourage students to proceed through the data analysis and complete the ELN prior to leaving the lab. Remember, your role is as their coach - help encourage them to get their work done now while help is available so they do not feel overwhelmed later. If they need to take a bathroom or snack break, encourage them to do so before returning to the classroom room to complete the exercise. Shut down/ clean up Unless there is an unforeseen issue, your students should be finished with the lab work before 5 pm. They are to leave the room in clean condition prior to leaving lab and returning to the conference room. Remind students to clean up before returning to the classroom. Students should do the following: Clean cuvettes with rinse methanol three times and leave the cleaned cuvettes in the rack. Empty the temporary waste container into the primary waste container labeled for this experiment. Rinse the flask into the primary waste using rinse methanol. Return the temporary waste container to the bench TAs should do the following shut down tasks before returning to the classroom: Encourage students to continue their work in the classroom until their ELN is complete. Turn off the UV-vis. Return the dye solutions to the freezer. If you are the last section of experiment, return all materials to their storage location in the prep room. Be sure that the primary waste container is capped. Remind students to clean up. Remind students to sign out with the time they leave and get your signature. Check the TA checklist for additional items to be completed.