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Meet the Magnets

ArrowThe 600 MHz NMR Magnet with 1-mm Triple-Resonance, High-Temperature Superconducting Probe



Vital Statistics

The 600 MHz NMR Magnet Strength 14.1 tesla
Type Superconducting
Bore width 52 mm (~2 inches)
Sample tube width 1 mm (~.04 inches)
Online since 2005
Cost (probe only) About $0.5 million
Operating temperature (probe) -253 ° C
(-424 ° F)
Minimum sample size ~5 microliters
Homogeneity 1 part per billion

Overview

Sample Tube

A drop of sample will fill this tube.

This instrument, located at our Advanced Magnetic Resonance Imaging and Spectroscopy program at the labís University of Florida campus, is not special because of its magnet. In fact, its 14.1 tesla magnet is pretty run-of-the-mill. However, when used with a unique probe developed by the MagLab in cooperation with Bruker, a company that makes research magnets, this instrument is more than special: It delivers the highest mass sensitivity of any probe at any frequency in the world.

To understand what that world record means and why it matters, letís get a little vocabulary out of the way: What the heck is a probe?

In a nutshell, a probe is a piece of equipment into which the sample is inserted; it is needed for nuclear magnetic resonance (the MRI machines used in hospitals are examples of NMR). Placed inside the magnetís bore, the probe contains a device called a radio frequency (RF) coil, which interacts with the magnetís field and atoms in the sample, sending information about what the sample is made of to a computer.

This particular probe, as you can see from the photos, is quite small – the tube inside it containing the sample is a mere 1 millimeter wide. This feat of engineering took years to complete, from conception to end product. Its size is an advantage when you have just a smidgeon of sample, sometimes the case when working, for example, with plant or animal materials. As long as your sample is highly soluble, you can find a wealth of information in a drop of liquid.

Probe
The sample tube goes in this probe, which is inserted into the magnet.

In one interesting application, MagLab scientists are studying the venom of the walking stick, promising research that could lead to better cancer drugs. In an early study from the 1960s, researchers milked 1,000 of these insects before accumulating enough venom for an analysis. Today, with this probe, a single milking would do the trick.

Another great thing about this petite package: Smaller RF coils result in more sensitive readings and more detailed information about the sample.

This probeís sensitivity is due not only to its small RF coil, but also to the fact that that coil is superconducting. Because the coil is cooled to -424 degrees Fahrenheit, or -253 degrees Celsius, current runs through it much more efficiently. As a result, it can pick up and pass along the signal from the sample much more effectively. (This probe, by the way, picks up signals from hydrogen, nitrogen-15 and carbon-13 atoms; thatís why itís called a triple resonance probe.) Also, cooling the coilís electronics reduces background noise that might otherwise interfere with the sampleís signal.

The analogy of a phone line helps illustrate this. If you have a bad connection, you can do one of two things to make the signal come across more clearly: Talk louder or reduce that irksome static. Either way (or both), you get a more efficient amplification of the same sound – just as a superconducting coil and/or a smaller coil give you a better NMR signal.

Finally, this instrument boasts "high homogeneity" – meaning that the field strength remains very even, at 14.1 tesla, throughout the experimental space.

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