Nuclear Magnetic Resonance
FAQs

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

A1. Please follow these steps:

1. Create a Facility Online Manager (FOM) account at https://fom.rice.edu/fom. FOM is required for instrument scheduling and billing.

2. Complete the required SEA new user paperwork forms (including the User Information Sheet and Agreement Form), which can be accessed on the SEA onboarding page:https://research.rice.edu/sea/about/becoming-sea-user

Once your FOM account is established and Rachel Berins (Rachel.Berins@rice.edu)receives and approves your signed paperwork, we can schedule your hands-on training on the NMR instruments.

Q2. What is NMR training focused on?

A2. Our basic NMR training session focuses on setting up routine 1D NMR experiments in ICONNMR, Bruker's automation software that allows fully automated acquisitions. If you are interested in advanced experiments, we also offer advanced NMR training sessions for your experimental needs.

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 each time they wish to set up experiments in non-automated mode.Failure to comply with these policies and rules may result in the suspension of NMR instrument access privileges.

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).

Users are responsible for any damage to the NMR instrument resulting from negligence or improper operation. 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 have 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 optimal sample volume for a 5mm tube is 600 uL (i.e., 40mm sample depth).
  • Dissolve your sample in an appropriate deuterated solvent.
  • Ensure the sample solution is homogeneous. Cloudy solutions will be harder to shim, which reduces the spectral resolution. If necessary, filter/centrifuge to remove the insoluble particles before transferring into an NMR tube.
  • Paramagnetic species in the NMR samples can 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 and melting points. You must not get any closer than 10 degrees to the boiling or melting point. When performing high-temperature NMR experiments, avoid using a sealed NMR tube because pressure can build up inside the tube
  • H2O content. All deuterated 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, consider using 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 an 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 signal-to-noise ratio (S/N) by decreasing the thermal noise in the probe coils. You can also increase the number of scans (NS)to improve S/N. Note that S/N is proportional to the square root of the number of scans. Therefore, to double S/N, NS should be increased by a factor of 4.

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

A11.

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