Obtaining a Simple 1H NMR

Use about 10 to 25 mg of a typical organic compound and this procedure will probably result in a fine NMR spectrum. Details for these seven-simple steps follow in paragraphs I and II.

1. Prepare the sample and place into a clean 5-mm NMR tube.
2. Remove reference standard (ethylbenzene in CDCl₃. and insert the NMR tube containing the sample into the spinner and then into the magnet.
3. Type DG to make certain the instrument is set up for protons under Exp1 and the solvent: CDCl₃ and type NT=6
4. Adjust the Z0 black knob from the LK screen, as required; must be locked.
5. Type S for the shim screen and adjust Z1C, Z2C, and lockphase with the proper black knobs.
6. Type GA to go acquire spectra, then type APH to make phase corrections.
7. If the spectra is satisfactory and get a printed copy type the macro PN2. [Or there is software to save the spectra on a floppy and print from NMR SpecManager.]

I. Preparing a Sample

Weigh approximately 20 mg (0.020 g) of the sample into a clean, dry vial. Add approximately 0.7 to 0.8 mL of deuterochloroform (CDCl₃) containing a small amount of tetramethylsilane (TMS) and swirl gently until the sample dissolves. Transfer the sample to a 5-mm NMR tube using a clean, dry Pasteur pipet. There must be approximately 5 cm of solvent in the tube. (Anywhere from 4 to 6 cm is fine, more than 6 cm is a waste of the expensive CDCl₃.) Finally, put a cap on the NMR tube and have an adequate label.

II. Setting Up the Instrument, Acquiring, and Printing Spectra

Warning! Remove all metal objects, wrist watches, and any magnetic media (i.e., credit cards and ATM cards) before approaching the magnet.

1. Enter your name and start time in the NMR logbook. Look to see that no one else is currently running an experiment on the instrument. Look to see if the last user noted any problems.

2. Turn on the monitor or CRT screen, type login, and enter your login name and password. Experienced users may eject the standard reference sample and place their sample into the magnets probe at this point but not beginners (see paragraph 6). The standard reference sample is ethylbenzene in CDCl₃.  The new user will find it easy to lock and shim the standard and then their sample, which is also dissolved in CDCl₃.

3. If you are not in EXP1 type JEXP1 <return> Type DG <return> and see if the prior experiment was for proton with your solvent and go to step 5. EXP1 is reserved from standard proton experiments for both Gemini's. The NMR has several different locations where you can run experiments. This places you in experiment 1, the usual location for acquiring routine proton NMR's.

4. Type SETUP(H) <return>
Loads the standard proton parameters. This is not necessary if the person before you was using the
standard parameters. If at any point you wish to view the parameters type DG. Set the value of NT=6 or some small number.

5. Type LK <return>
Displays the lock signal. If the NMR is not locked, get help. A long division sign signifies lock and a sine wave not locked..

6. First eject the standard reference sample and insert your sample into the spinner and magnet.
Depress and hold down the black eject button on top of the left leg of the magnet to eject the sample.
Remove the standard sample from the Teflon spinner and put it into the storage block. Insert
your sample into the spinner and adjust its depth using the paper gauge on the right magnet leg. Wipe off
the lower part of your sample tube with a KimWipe. While depressing the eject button insert your sample into the magnet and then slowly release the eject button so that the sample slowly drops into the magnet. It is very important that you depress the eject button while you insert the sample. Otherwise you risk breaking the NMR tube in the probe. This could result in damage to the instrument. Never insert the spinner without an NMR tube in it. Never inject more than one sample. Never insert the spinner upside down. Avoid touching the black ring with two white dots. Oil on hands will contaminate the spinner and force cleaning of the upper barrel.

7. Make sure that your sample is locked and spinning (Adjust Z0, zero).

The spin meter is on the left leg of the magnet. The spinning rate should be between ~10 and ~20 on the meter. If the sample is not spinning, try ejecting the sample, cleaning the tube and spinner with a Kimwipe, rechecking the depth, and then reinserting it. Do not adjust the spin rate.

8. Type S <return>.

Adjust the ZC1 and ZC2 knobs so that the signal on the "X1" or "X5" meters are maximized. S activates the interactive shim controls. With LPOWER ~ 17 and LGAIN = 20 the lock level should be approximately 70, or less. If the lock level goes above 100, use the PF5 function key to activate the LPOWER and LGAIN adustments. Turn LPOWER down until the lock level is around 60 to70. Then use the PF1 function key to return to shimming ZC1 and ZC2. Do not adjust any other shims. Maximize the lockphase

9. Type GA <return>
GA (Go Acquire) initiates the acquisition of the spectrum. The upper left hand corner of the screen
displays the status of the acquisition. It takes about 1 minute to acquire the data. (If you get an error message that says "...Lower PW" it means that your sample is too concentrated for the NMR to handle with its standard parameters. Normally the PW will be automatically lowered in not, type PW=3 (or half the current value), and then try GA again.)

10. After the NMR displays the spectrum, type APH <return>.
The NMR will automatically process the data and display the spectrum when it is done acquiring. APH will automatically phase it.

11. Type the macro PN2 to print your spectra.

12. Eject your sample and insert the reference standard. If someone is waiting to use the NMR you can give them the spinner and allow them to put their sample in. Otherwise, place the standard sample back in the spinner, adjust its depth, and carefully place it back in the magnet while depressing the eject button.

13. Type LK <return>. Make sure the NMR is locked.
Check to make sure that the sample is locked. Always leave the NMR locked on the standard sample and leave the lock screen turned on!

14. Log off and turn off the monitor. If another users is beginning to use the instrument log off.

15. Enter the ending time in the logbook and note any problems.