Q1. What SEA paperwork do I need to finish before NMR training?

A1. You will need to Join SEA to become a user. After your account is activated, please contact Meri Dix (meri.c.dix@rice.edu) or Rachel Berins (rb108@rice.edu) to request NMR training for the instrument you are interested in.

Q2. What is NMR training focused on?

A2. Our basic NMR training session focuses on setting up routine 1D NMR experiments in ICONNMR. ICONNMR is the automation software that allows fully automated acquisitions. If you are interested in advanced experiments, we can have an advanced NMR training session for you.

Q3. What are the benefits of using ICONNMR?

A3.

• Increase cost efficiency: set up all experiments before you leave the lab in the evening and have all results available when you start your next day.
• Keep an eye on your cost: careful tracking of each user’s usage times.
• Deliver your spectra data per email to respective users.
• Make it accessible for nonexperts and experts.

Q4. Can I run my NMR experiments (multidimensional NMR, DOSY, variable temperature, etc) in a non-automated mode?

A4. First of all, users need to request NMR training for these advanced experiments.

After training, users must get permission from Dr. Quinn Kleerekoper or Dr. Xu Wang to set up experiments in non-automated mode each time when using the instrument. Failure to follow these policies and rules may lead to suspension of the access privilege and other possible penalties.

This is because:

• We need to know how much time a user spends on the instrument (for billing).
• We want to make sure your NMR operations and experimental parameters are correct (for probe safety).

If the NMR probe is damaged due to improper NMR operations/experimental parameters, PI needs to pay for repairs because we do not have parts/service contracts for NMR instruments.

Q5. How do I select the right NMR tubes for my NMR study?

A5. Please use medium- to high-quality 5mm NMR tubes. We strongly discourage using "disposable" tubes on any NMR instruments. Cheap tubes don’t process perfect cylindrical symmetry, which would limit the attainable field homogeneity. We recommend the precision grade NMR tubes for 600 MHz NMR, such as the Wilmad (535-PP-7), Norell (509-UP-7/S-5-600-7), or NewEra (NE-UP5-7). NMR tubes must be free from scratches on the glass as this distorts the cylinder in which the sample is confined.

Q6. How do I prepare solution NMR samples?

A6.

• The optimum sample volume for a 5mm tube is 600 uL (i.e., 40mm sample depth).
• Use deuterated solvent for your sample.
• The sample solution should be homogeneous. Cloudy solutions will be harder to shim which reduces the spectral resolution. Consider filtration/centrifugation to remove the insoluble material if your sample is unclear.
• Please note that paramagnetic species in the NMR samples cause the broad line width and unusual chemical shifts. This might also affect the signal frequency of your deuterium solvent. You will have problems with the auto lock and auto shimming. If applicable, please remove paramagnetic species from your NMR sample.

Q7. Why do I need the deuterated solvent in my NMR sample?

A7. Deuterated solvents are used in solution NMR for two reasons:

• Provide a deuterium lock signal. The magnetic field tends to drift slowly. Modern NMR instruments measure the deuterium absorption of the solvent and adjust the field strength to keep the magnetic field constant.
• Avoid very large solvent signals in the 1H NMR spectrum.

Q8. How do I choose a suitable deuterated solvent for my compound?

A8. Factors to be considered when choosing a suitable solvent are:

• Good solubility.
• Make sure the NMR signal from the solvent doesn't interfere with the solute. In 1H NMR, the observed solvent resonance arises from the residual protonated species since deuteration is not 100% complete.
• Boiling point and melting point: You must not get any closer than 10 ^oC to the boiling or melting point. When performing high-temperature NMR experiments, it is good practice not to use a sealed NMR tube.
• H₂O content: All solvents are hygroscopic to some degree and should be exposed to the atmosphere as little as possible to prevent them from becoming wet. The H₂O peak can be strong and broad, and its chemical shift can vary according to solution conditions. The presence of an H₂O peak will degrade the quality of NMR spectra. To minimize the H₂O content, you can consider using the deuterated solvents in single-use ampules.

Please read "NMR Solvent Chart" for more information.

Q9. How to clean NMR tubes properly?

A9.

• For routine cleaning, rinsing with a suitable organic solvent or distilled H₂O a few times is usually sufficient.
• More stubborn soiling is best tackled by chemical rather than mechanical means. Soaking in detergent or strong mineral acids is recommended. Chromic acid is not good for cleaning since the paramagnetic Chromium VI adversely affects your NMR results.
• Tubes should not be dried by subjecting them to high temperatures for extended period of time as this tends to distort them.
• Avoid contamination of the outside of the NMR tube because this leads to the transfer of the contaminants into the probe head.

An NMR tube cleaner allows easy cleaning and rinsing.

Q10. My sample quantity is low. How can I improve the signal-to-noise ratio (S/N) of NMR signals?

A10. If your sample quantity is low, choose an NMR instrument equipped with a cold probe (see instrument specifications). This is because the cold probe greatly improves S/N by decreasing the thermal noise in the signal detection pathway. In addition, you can increase the number of scans for your experiment. Note that S/N is proportional to the square root of number of scans. If you want to double S/N, then NS should be increased by a factor of 4.

Q11. What are the sample requirements for a solid-state NMR study?

A11.

• ~85mg solid sample is required for a 4mm ZrO₂ MAS rotor.
• Solid samples must be finely powdered. Samples can be finely grounded using mortar or a ball mill.
• All samples must be completely dry.
• Samples must not be conductive or ferromagnetic.