Carbon-13 Spectra

 

Note: Where the instructions tell you to type a command, only type what is within the quote marks, do not type the quote marks.

Follow the initial steps of sample preparation, logging on, locking and shimming, that are used for a routine proton experiment.

RUNNING THE EXPERIMENT

1. Pull down the "File" menu, move to "open" and release on "data set owners".

2. Click on "nmr".

3. Pull down the "file" menu, move to "open" and release on "data sets by name".

4. Click on "stdcarbon". Old data may be displayed. Ignore it.

5. Pull down the "file" menu, move to "new" and release. Click in the box after "name" and type in a new name for your sample. Be sure to click in the box after "user" and to type in your owner name. Then click on "save". You are now set up to collect a standard 1D carbon spectrum.

6. The broadband probe is very likely to be left tuned for carbon spectra, so you may proceed with the next step. If the tuning has been changed, another step is required at this point. Obtain the assistance of an expert.

7. Type "rga" (return) and wait until the automatic receiver gain adjustment is complete. Display will read: "rga: finished".

8. Type "zg" (return). You can watch the accumulation of the FID by pulling down the "acquire" menu and releasing on "observe FID window". When the experiment is complete, the message at the bottom will display: "checklockshift: finished".

9. Type "em" and then type "ft". The screen will automatically display the Fourier transformed spectrum.

PHASING

10. Increase the amplitude as appropriate and then click on "phase".

11. Click on "biggest".

12. Click and hold down the mouse button on "PH0" and roll the mouse up or down as needed. Adjust the spectrum until all of the peaks are above the noisy baseline. Ignore the fact that the baseline may be curved. Release when the phasing looks good.

13. Click on "return" and "save and return".

14. Type: abs (return) to even out the baseline.

OPTION

15. Rerun the acquisition with a narrower spectral width if you wish. The number of scans can be increased at this time, too.

16. To narrow the spectral window, click in the black area of the screen and get an arrow pointing down on the spectrum trace. Click the center mouse button at the left edge of the desired new spectrum width and again at the right edge. The new size will increase to fill the screen display.

17. Click on "utilities". Click on "sw-sfo1" (return). The new width is now set.

18. Repeat the acquisition by typing "zg" (return). When the "checklockshift: finished" message is displayed, type "em" and "ft" and repeat the phasing process. Click on the "return" button and "save and return".

CALIBRATING

19. Identify the cluster of three peaks associated with deuterochloroform. Click the cursor on the screen and get an arrow pointing down riding on the spectrum. Position the arrow just to the left of the cluster and click the center mouse button. Move the second arrow just to the right of the cluster and center click again.

20. Click on "calibrate" and move the arrow until it is positioned exactly over the center of the three peaks. Click the center mouse button and type "77" (return).

PLOTTING OPTIONS

21. Usually 13C spectra are not integrated.

22. Peak-picking setting the title and plotting are similar to those actions for proton spectra.

23. Remember to pull down the "output" menu, move to "define/show plot region" and release on "retain CX".

24. Type "view" for a preview. Type "plot" to plot.

LOGGING OUT

25. Pull down the "file" menu, release on "exit".

26. Double click on the close box on the winterm window.

27. Pull down the "desktop" menu and release on "log out". Click on "yes".

IMPORTANT: Put a standard sample back into the spinner and release the lift button on the keypad. You may also turn on the spinner.

REMOVING THE SAMPLE

28. On the keypad, turn "Lock on/off" to off. (Light goes off.)

29. Turn spinner off. (Light off.)

30. Turn "Lift" to on. (Light goes on.)

31. Retrieve sample from spinner.

32. Replace a sample and turn the "Lift" button to off.