Frequently Asked Questions
FFC has been used for many applications. The more well-known areas of application for FFC NMR are for the study of MRI contrast agents, proteins and other biomolecules, polymers, materials such as liquid crystals and studies of rock pore size, however there are many new areas of application being studied by research groups around the world. For more information on applications of FFC NMR relaxometry, please refer to the applications and literature pages.
If you would like to find out more about getting samples tested, please refer to the sample testing page.
FFC NMR relaxometry is able to measure all forms of samples, with the exception of gases. FFC NMR is a non-destructive method and samples can be measured in their actual state without the need for dissolution in particular solvents or filtration. Generally a standard 10mm NMR tube is used and filled to approximately 1 cm3 volume. For example:
- Solids – dissolution is not strictly necessary (organic and inorganic salts, crystalline solids and amorphous solids; polymers)
- Liquids (aqueous and organic solutions, viscous liquids)
- Liquid crystals
- Colloids (Emulsions, gels, creams, aerosols)
- Complex mixtures (e.g. foodstuffs, rock cores)
The length of time it will take to run a full 1H NMRD profile on a sample will depend principally on the length of the spin-lattice relaxation time, T1, for the individual sample and on the number of points needed to give a satisfactory NMRD profile.
The T1 of samples will vary widely and depend on whether they are “fast” or “slow” relaxing samples. It may be possible to refer to similar examples in the literature to understand the length of T1 for a given sample. For example:
- Fast relaxing samples, such as Gadolinium-based MRI contrast agents, may have a T1 in the range of 0.02 seconds. One measurement of the relaxation rate 1/T1 at one magnetic field strength would require 20 seconds.
- Samples which are slow to relax, such as proteins in solution, may have a T1 in the range of 5 seconds. One measurement of the relaxation rate 1/T1 at one magnetic field strength would require 250 seconds.
To obtain a reasonable NMRD profile, around 20 measures of relaxation rate at different magnetic field strengths would be needed. Evidently if fewer points of the NMRD profile are required, the time to run a sample is reduced or vice versa if more points are needed. For example, more points may be required if trying to define a nuclear quadrupole resonance (NQR) peak in the NMRD profile of samples such as proteins.
On the Stelar FFC relaxometers it is possible to obtain NMRD profiles (relaxation rates in T1 as a function of magnetic field strength) for other important nuclei, or so-called “heteronuclei”, such as 2H, 13C, 19F, 7Li, etc. These can help to provide important structural information connected to the presence of a particular nucleus within a substance. For further information refer to the section on Heteronuclei in the applications pages.
- Sample temperature is a basic parameter in NMR relaxometry which can be set and controlled by using a Variable Temperature Controller (VTC).
- The range of temperatures from -140 °C to 140 °C can be obtained with the VTC, with a precision of 0.1 °C.
- Incorporated calibration procedures allow fine sensor and set point calibration in order to minimize the temperature gradient of the sample.
- FFC relaxometry is particularly useful for measuring slow molecular dynamics: many molecular processes (motions) occur in the range between nanoseconds and milliseconds. These are difficult to measure at high magnetic field strengths but are much more evident at very low magnetic field strengths.
- FFC relaxometry may be used as a comparative technique to understand differences between samples which are apparently the same by many other analytical methods: differences in the spin-lattice relaxation rate, 1/T1, of a substance or complex system are generally more evident at low fields and thus relaxation rate measurements made with fixed field magnets may not be able to reveal critical differences between substances or systems which appear chemically to be the same.
- The NMRD profile may be used as a “fingerprint” of a particular substance or complex system and thus is useful for identification purposes and may be of particular use in quality control applications.
(see also why is FFC NMR relaxometry useful above)
- Fast Field Cycling Relaxometry is the only NMR method allowing the determination of the spin-lattice relaxation time constant (1/T1) over a range of magnetic fields (from about 10-6T up to the maximum field allowed by the magnet) using one instrument.
- With an FFC relaxometer, there is no need to adjust the RF amplifier or tune/match the probe at each frequency/magnetic field strength, as would be required to attempt the measurement of spin relaxation rate using a conventional NMR magnet system.
- Fixed field magnet systems are not able to measure nuclear spin relaxation down to low magnetic field strengths due to sensitivity limits: the NMR signal-to-noise ratio decreases with the intensity of the magnetic field. In practice, the lowest magnetic field strengths used are a few MHz (commercial instruments generally go down to 2 MHz), whereas an FFC relaxometer is able to overcome these limitations and can measure nuclear spin relaxation down to a few kHz.