Lithium Detection

Lithium has two isotopes, Li6 and Li7, with a natural abundance of 7.6% and 92.4%, respectively. Li6 (spin=1) has a 50-fold smaller quadrupolar moment than Li7 (spin=3/2), making Li6 signal sharper than Li7, particularly in an organometallic system with bound lithium. But Li6 sensitivity is 420 fold lower than Li7 at natural abundance, making both Li6 and Li7 useful depending on the resolution and sensitivity tradeoff. Li6 enrichment should yield both better linewidth and sensitivity. Both nuclei have a chemical shift range from -16 to 11ppm.

Referencing (for both Li6 and Li7)

As usual, choose one of several referencing methods:

1. For rough referencing with lock turned on, type setref
2. Add TMS (or DSS for aqueous solution), reference TMS/DSS 1H signal to 0ppm (in exp1). In Li6/7 experiment (in exp2), type mref(1,2) or use other methods as discuussed here.
3. Use a separate sample (9.7M LiCl in D2O) to reference Li6/7 peak to 0ppm. Without shimming, then collect data from your sample under same experiment, running unlocked.

One-pulse Li7 detection on NMR500 with SWP probe

Li7 experiment should be run locked if possible. If you have done Li6 experiment with the lock cable disconnected, re-connect it. Ideally, you want to have have two samples:

1. The actual sample with your compound
2. a 9.7M LiCl sample in D2O for testing and referencing

Step 1: Lock and shim

• Load your sample. Under exp1, type initshims to load standard shims.
• Type setexp('Li7') su to load standard Li7 detection experiment.
• Change solvent, lock and shim as usual.

Step 2: Tune probe and replace 1/4-wavelength cable

• Type su in exp1
• Install the tuning stick labeled 13T into the empty slot under the probe.
• Tune channel 1 to Li7 using X-channel/broadband preamp connecting cables. After tuning, reconnect cables to original configuration.
• Replace the current 1/4-wavelength filter with one covering 194.3MHz.

Step 3: Collect data

• Set nt=1000 (or other large number) and collect data. Stop experiment whenever you are satisfied with signal.
• Adjust spectrum width and recollect data. Leave 10% baseline area on each side of spectrum. Choose one of two methods:
• To move transimtter (center of spectrum) to a specific cursor position, type movetof. Adjust sw accordlingly.
• To move spectral window to include a region enclosed by box cursors, type movesw.
• Type go or ga after change.
• Reference spectrum with procedure above
• If no signal is seen, check with a standard 9.7M LiCl (in D2O) sample or talk to staff.

Step 4: Finishing off: reconnect cables and tune X-channel back to C13

• Type tn='C13' su under current experiment.
• Load the Idle sample (100% cdcl3)
• Remove 13T stick from probe. Tune X-channel (channel 1 on tuning interface) back to C13. Reconnect cables back to original configuration.
• Reconnect the lock channel cable to probe.
• Replace the 1/4-wavelength cable with the default cable for C13 (125.7 Mhz)

One-pulse Li6 detection on NMR500 with SWP probe

Note that the resonance frequency of Li6 is very close to that of deuterium with a ratio of 1:1.043. With the filters available on nmr500, it is recommended that Li6 experiment is run unlocked as instructed below.

Ideally, you want to have two samples:

1. The actual sample with your compound
2. A Li6/7 sample with 9.7M LiCl in D2O. This is used for referencing and testing if needed.

Step 1: Lock and shim

• Load your sample. Under exp1, type initshims to load standard shims.
• Type setexp('Li6') su to load standard Li6 detection experiment.
• Change solvent, lock and shim as usual.
• Go to the lock control panel and turn lock to OFF.

Step 2: Tune probe, disconnect lock cable and replace 1/4-wavelength cable

• Type su in exp1
• Install the tuning stick labeled 7pF into the empty slot under the probe.
• Tune channel 1 to Li6 using X-channel/broadband preamp connecting cables.
• After tuning, before reconnect cables to original configuration, remove the square H2 band rejection filter labeled NR-76.75-10-... connected to broadband preamp. Connect the X-channel probe cable to the other filter.
• Disconnect the lock cable from probe.
• Replace the current 1/4-wavelength filter with one covering 73.6MHz.

Step 3:Collect data

• Set nt=1000 (or other large number) and collect data. Stop experiment whenever you are satisfied with signal.
• Adjust spectrum width and recollect data. Leave 10% baseline area on each side of spectrum. Choose one of two methods:
• To move transimtter (center of spectrum) to a specific cursor position, type movetof. Adjust sw accordlingly.
• To move spectral window to include a region enclosed by box cursors, type movesw.
• Type go or ga after change.
• Reference spectrum with procedure above.
• If no signal is seen, you can load a standard 9.7M LiCl (in D2O) sample, without changing anything (run unlocked) do a quick test (nt=1 should give good signal). If you still don't see signal with the standard sample, check cabling and tuning and talk to staff.
• Save data.

Step 4: Finishing off: reconnect cables and tune X-channel back to C13

• Type tn='C13' su under current experiment.
• Load the Idle sample (100% cdcl3)
• Remove 7pF stick from probe. Tune X-channel (channel 1 on tuning interface) back to C13. Reconnect cables back to original configuration.
• Reconnect the lock channel cable to probe.
• Replace the 1/4-wavelength cable with the default cable for C13 (125.7Mhz)

H. Zhou updated Dec 2010