All new users of the NMR facility are required to take a one hour training session before being checked out by the staff. Training sessions for new users are scheduled every month. Please contact Eugenio Alvarado for an appointment.
Please review the NMR Facility Rules, Safety Information (see below) and Instrument Care and Good NMR Practices (see below) before your training session and before using the instruments for the first time. A VNMRJ Training Guide and other information regarding advanced experimental procedures can be found in the Documentation section.
A basic understanding of FT NMR is essential to efficiently operate the spectrometers. Good references to read are found in:
- Claridge,Timothy, "High-Resolution NMR Techniques in Organic Chemistry". Pergamon Press 1999, Chapters 1-3
- Sanders, J. K. M., and Hunter, B. K., "Modern NMR Spectroscopy. A guide for Chemists”, 2nd Ed. Oxford Press 1993, Chapter 1
- Derome, A., "Modern NMR Techniques for Chemistry Research". Pergamon Press 1987, Chapters 2-4.
The following risks are mimimised by preventing access to the NMR rooms to anyone other than the NMR staff and trained users. Anyone else needing to enter the NMR rooms should only do so in the presence of one of the NMR Lab staff.
Superconducting magnets of NMR spectrometer are always energized. Strong fields are produced not only on the inside but also outside the magnet. A maximum magnetic field of 5 gauss (0.5 mT) is generally considered safe for most situations. The distance to the center of the magnet that produces a field of 5 gauss depends on the magnet. In our spectrometers, the 5 gauss perimeters are as follows:
|Frequency (MHz)||Horizontal Distance||Vertical Distance|
|500||2.8 m (9.2 ft)||3.6 m (11.8 ft)|
|400||2.2 m (7.2 ft)||2.8 m (9.2 ft)|
|300||1.8 m (6.0 ft)||2.0 m (7.0 ft)|
|200||1.5 m (4.9 ft)||1.5 m (4.9 ft)|
Metal objects must remain outside the 5-gauss perimeter. Strong magnetic fields surrounding the NMR spectrometers attract objects containing steel, iron, and other ferromagnetic materials. This includes most ordinary tools, electronic equipment, compressed gas cylinders, steel chairs, and steel carts. Unless restrained, such objects can suddenly fly toward the magnet which can cause personal injury and extensive damage to the probe and magnet. The greater the mass of the object, the more strongly it is attracted by the magnet. The shorter the distance to the magnet, the stronger the force. Only non-ferromagnetic materials should be used near the instruments. This is probably the main risk because it is one with which most people are unfamiliar. Even metallic belt buckles, steel tipped shoes, etc., may be strongly attracted to a magnet.
Here you can see a video of a demonstration of what happens when you get a heavy iron object too close to a magnet.
Floppy disks, tapes, cards with magnetic strips, cellular phones, laptops and mechanical watches should remain outside the 5-gauss perimeter. Strong magnetic fields surrounding the NMR spectrometers can damage the strip of magnetic media found on credit cards, ATM cards, driver's licenses, and other kinds of cards. Floppy disks, tapes, cellular phones, and laptop computers are also susceptible to damage inside this perimeter. Mechanical wrist and pocket watches will also malfunction and may be permanently damaged when exposed to a strong magnetic field.
Individuals with medical devices (e.g. cardiac pacemakers and metal prostheses) must remain outside the 5-gauss perimeter. The NMR spectrometers generate strong magnetic fields that can affect the operation of some pacemakers and harm implanted or attached devices, such as prosthetic parts and metal blood vessel clips. Persons with these types of medical concerns should contact their physicians about the possible health risks before entering the Facility.
In the event of a "magnet quench", leave the room immediately and contact the NMR Facility Staff as soon as possible. A magnet quench is the sudden loss of supercondutivity in the magnet's main coil that produces a rapid and vigorous release of helium gas from the dewar. A quench warranting evacuation would be obvious by the noise of the escaping gas and clouds of condenses water vapor. The rapid expansion of liquid helium or nitrogen to gas can displace breathable oxygen in an enclosed space creating the possibility of asphyxiation. Do not re-enter the room until the oxygen level has returned to normal. Our lab is equipped with oxygen sensors that sound an alarm when the oxygen level falls below a safe value. If the alarm sounds, evacuate the room immediately and stay out until it goes off.
Only individuals who have had special training should transfer cryogens to the instruments. Handling cryogens is dangerous and can cause serious burns. Safety glasses and gloves should be worn during the transfer of all cryogens. The cryogens used are liquid nitrogen and liquid helium. Boiling point temperatures: liquid nitrogen: -196° C and helium: -269° C. Color: none; toxicity: very low; fire hazard: non combustible. The expansion ratio of liquid helium at room temperature is about 740:1, which means that one liter of liquid helium expands to about 740 liters of helium gas. The main risks are of burns when handling cryogens and of asphyxiation if a magnet quenches. These are minimized by only allowing experienced staff to fill the magnets with liquid nitrogen and liquid helium.
Instrument Care and Good NMR Practice
Do not exceed the boiling or freezing points of your sample. A sample cooled below the freezing temperature may crack the tube and release the solution into the probe. A sample heated near or above the boiling point may cause the tube to explode or its cap may pop out and spill the solution into the probe. In both cases the cleanup is very time consuming and the probe may be damaged. Repairs can be very expensive.
Notify the staff immediately if a sample is broken inside or around the magnet. The probe needs to be removed and inspected or cleaned before normal operation can proceed. Failure to do so may result in further damage and more expensive repairs. Probe removal and cleaning is very time consuming and repair can be expensive, so please handle your samples with great care around the magnet.
Handle the spinners with care. They are deceptively simple but they are precision machined and very expensive. Don't drop them!!! (please). When they are dropped, they may loose balance resulting in noticeable "spinning side bands" and spikes around the peaks in the spectra. Don't get them dirty. Make sure the outside of your sample tube is clean and free from residues before you come to the lab and you insert it in the spinner. If a tube is broken inside the spinner, clean all sample and glass residues and notify the staff. Please don't leave the spinner dirty as we don't know if the residues are toxic. Grab the spinner only from its upper rim (the black band with white dots), and only with clean hands. Otherwise, over time grease from all users' hands will accumulate in the spinner and inside the magnet preventing samples from spinning properly.
Be very careful with sample tubes as they are fragile and break easily. Sample tubes can break off when inserting them or pulling them off the spinners. They can also break when they are inserted in or removed from the magnet. In most cases, sample tubes break because the user is impatient or careless, tries to take quick spectra and attempts to perform these insertion / extraction operations more quickly than he/she should. Sample spills around the computer and keyboard should be cleaned immediately. Do not use acetone for cleaning as it damages plastic surfaces. All pieces of glass must be located and removed.