FAQs

Non-medical applications of NMR

Current Industrial Applications and Applied Research

The applications in industry are widespread. Routine analysis of chemicals is probably the most common use but the NMR technique is sufficiently flexible to be used for example to measure the water/fat ratio in foods, monitor the flow of corrosive fluids in pipes, or to study the structure of catalysts.

Industrial applications can be divided into chemical, biological, paramedical, data processing, and non-destructive testing. This overview is not exhaustive, but it gives some highlights of the possible applications. It underlines the difficulties, challenges, and possibilities of interdisciplinary research and teaching.

Chemical Applications

General Remarks

Hydrogen-1 (1H) and carbon-13 (13C) NMR spectroscopy of solutions of chemicals are indispensible to the organic chemist in identifying the products of the latest reaction. The analysis is quick and simple and does not require an especially pure sample. This type of work is probably the most common type of NMR work done throughout the world and will continue to be so for many years. Yet, it does not begin to hint at the enormous versatility of the NMR technique and the wide range of information which can be obtained from different systems.

Oil and Coal Analysis of low molecular weight fractions of oils can be done by NMR, although other techniques do exist. The higher molecular weight fractions which are very viscous or even solid are more difficult to analyze but solid-state NMR techniques can be very useful. Solid-state 13C NMR has been performed on kerogens (an immature type of coal). The information obtained when used in conjunction with other types of analysis can be used to predict if the kerogen comes from a site which is gas-forming or oil-forming. Such information is extremely valuable when planning an exploration and drilling program. Among the possible new applications in this area is the development of a transportable MRI/MRS system which can be flown into a potential drilling region.

Catalysts called zeolites are used in large quantities by the oil industry to crack the higher molecular weight fractions to produce the smaller carbon molecules used in motorcar and heavy vehicle fuels. The zeolites are a complicated group of molecules composed mostly of silicon and aluminium. Solid-state silicon-29 (29Si) and aluminium-27 (27Al) NMR has been used extensively to study the structure of these molecules since an understanding of the way they work can lead to the choosing or designing of more efficient types of catalysts.

The accurate measurement of flow in pipes is a difficult problem for many industries. Oil in pipes (or even pipelines), fluidized coal, corrosive fluids, etc. have all been measured with NMR and a commercial NMR flow-meter has been available since 1968.

The non-invasive nature of NMR makes it extremely suitable for systems with unpleasant chemicals or extreme pressures, but despite excellent results in a few key examples there is room for much greater use of NMR monitoring of flow, e.g. flow-meters for oil-pipelines with simultaneous qualitative assessment of the transported oil.

Recently there has been quite a lot of effort put into spectroscopic and imaging studies of drilling cores. The spectroscopic studies have reported correlations between the NMR results and the mineral content, the pore geometry, and the surface chemistry of these rocks. It is hoped that this will either lead to new insights into the geology of the rocks or that NMR will be a quicker, simpler or cheaper method at obtaining the same information. MRI is being used to get a map of the three-dimensional distribution of oil and water in the cores and eventually will be able to monitor the flow of oil and water through cores. This information is vital to the models used to predict oil extraction from oilfields, where a 1% improvement represents millions of dollars of income gained or lost.

Plastics and Polymers

Some samples are mainly of interest as solids. Important examples are found in polymer science where it is the properties of the solid which are important and not the individual subunits which go to make up the solid. Solid-state NMR is used to study how plastics are put together, to relate their chemistry with their known physical properties. This information can be used to help improve the plastics and develope new ones. There are very few alternatives to NMR for getting this type of information from polymers.

Liquid Crystals

Liquid crystals are used in watches, calculators, and television and computer screens. They are also very difficult to study by other means than NMR. Just like the plastics, information about the packing of the molecules shows how structure relates to functional properties and so can help in creating new products.

Pharmaceuticals

High resolution NMR is a valuable tool to use when identifying and characterizing new drug molecules. It is possible for molecules to exist in two or more different forms or polymorphs in the solid state and solid-state NMR can be used to detect this. The polymorphs may have different biological activity which may cause a manufacturer to try to isolate one or another form. Furthermore it might prove possible for a competitor to by-pass patents if the existence of polymorphs has not been accurately documented.

Cement and Concrete

The study of the hydration process in cement is of great interest to the industry. Increasing the speed of hydration and the degree of hydration are both highly desirable since they increase the speed of setting and the strength of the concrete. However, both processes were rather difficult to quantify until it was shown that they can clearly be seen in solid-state 29Si spectra of cement. Changes in the concrete can be followed over periods of 90 days or more and thereby one can characterize the effect of different additives on the curing process.

Wood Pulp and Paper

The pulp and paper industry uses the complex mixture of high molecular weight compounds from wood pulp as its raw material. Solid-state NMR has been used to characterize the pulp and it can be used to determine the effect of different mechanical or chemical treatments of the type of pulp produced. Possibilities might also exist for the monitoring of pulp production in the factory.

Explosives

Whilst it is not possible (or at least not safe) to examine explosives directly it is possible to study chemical analogues of explosives like acetyl cellulose to improve understanding of the chemical structure of such materials. By relating chemical structure with functional properties one can help in the designing of safer and more efficient explosives.

Leather

Attempts are being made to replace chromium salts in leather tanning by environmentally friendlier aluminium salts. It seems possible that solid-state 27Al NMR can be used to help to characterize tanned leather.

Imaging of Solid Materials

Imaging of solids is in its infancy. Like medical imaging the nucleus being observed is 1H, but unlike medical imaging where the signal is relatively sharp and long lived, the signal from the proton in solid materials is generally rather difficult to detect since it is a very broad signal which lasts for a relatively short time. The purpose of such experiments would be to test non-destructively the various plastics and polymers used increasingly in modern manufacturing.

At present most published images are typically of a block of a solid material with holes of varying size drilled in it to demonstrate the resolution of the technique. There is one recent example of the use of MRI to observe solid rocket fuel prior to combustion. The packing of the solid fuel can have a large impact upon the burning properties. Conventional analytical techniques would either disturb the packing or prevent the sample being used in an ignition experiment. By the use of solid-state MRI it was possible to image samples before ignition tests and so directly correlate the effect of packing on burning properties. However, it was hardly more than twenty years ago that people were publishing MRI cross-sections of lemons and other fruits. MRI is now used routinely in hospitals throughout the world, and MRI of solids will probably make substantial progress in the next ten years.

Biological Applications

Food

Water content and fat/water ratio are two important parameters in many manufactured foodstuffs. Control of product quality may depend critically on them, but the traditional chemical methods of measurements may take between a few hours to a day to complete. NMR methods exist to make such measurements in less than a minute which is fast enough to help in the control of the production line. Some companies already use spectrometers dedicated to this sort of work, but there is still room for a huge expansion in the market.

A major problem is that whilst the routine analysis is a totally trivial task, it may take many weeks for a research scientist and a line manager to develop a suitable method for each particular analytical task, and the number of suitably trained scientists is very small.

Another area of routine analysis is that of wine. The European Community is currently developing an NMR test for the quality of wine, particularly to detect glycol adulteration. A routine method for determining the alcohol content in fermentation vats in two-three minutes has recently been published. NMR is also useful as a research tool in food science.

31P NMR spectroscopy has been used to demonstrate the hydrolysis of the food additive sodium tripolyphosphate (E 400) when it is added to meat, and chlorine-35 (35Cl) NMR was used to show how salt (sodium chloride) interacted synergistically with this additive so that a smaller amount of it still produced the desired effect. Detailed studies have been made of starch and carageenans, a polysaccharide obtained from seaweed and used in large quantities in food manufacturing.

Starch and carageenans are important in creating the correct texture in many foods and a fuller understanding of their properties will help in production of cheaper food of a higher quality and in the more efficient use of raw materials. MR imaging is beginning to be applied to foodstuffs as well. An early example was of chocolate showing how heating to 40° C and then cooling produced a permanent change in the chocolate. More recently the effect of freeze-thaw cycles on the structure of soft fruit and vegetables has been followed, and a particular promising use is the monitoring and visualization of the fat content of farmed fish (e.g. aquaculture of salmon).

Agriculture, Forestry, and Environment

NMR techniques have only recently begun to be applied to plant systems but one major area already established is the phosphorus and nitrogen nutrition of plants. Basic research in this area can hopefully lead to a more efficient use of fertilizers and thereby lead to reduced pollution of rivers, lakes, and the seas.

MR imaging of plant systems is even younger than spectroscopy but in one study of frost damage in pot grown pine and spruce seedlings it was possible to detect damaged and dead root systems weeks before the shoots showed any sign of damage. For instance, with Sweden alone producing 600 million seedlings per year at a price of roughly SKr 5.00 each there is considerable financial incentive to prevent frost-damaged seedlings being planted out. As a basic research tool MRI of intact root systems could be invaluable in increasing our understanding of how root systems develop, and so help in tackling problems like optimizing the uptake of nutrients (essential in nutrient-poor soil) or in preventing the blowing over of forest trees ("wind throw") which is a source of major economic losses.

Solid-state 13C NMR studies of soil have helped soil scientists to understand the rather large and complex organic molecules present in soil. For example, the chemical analytical methods used before the advent of solid-state NMR had seriously underestimated the percentage of aliphatic carbon groups as against aromatic carbon groups. An understanding of soil chemistry is important when studying the nutrition of plants and when considering the environmental effects of, e.g., acid rain or radioactive fall-out after the Chernobyl nuclear power plant accident.

A full understanding of the consequences caused by increasing levels of green-house gases (especially carbon dioxide and methane) must include the whole of the carbon-cycle. The soil is an important element of this cycle having huge amounts of carbon temporarily stabilised in the form of humus. Direct monitoring of pollution is also possible, particularly in adverse environments, e.g. the artic seas. The size of mussel populations, counted by divers, are currently used as an indication of pollution. Recent laboratory results have shown quite distinctive changes on the 31P spectra of mussels when subjected to low doses of petrochemicals (benzene, phenol, formalin) or heavy metals (cadmium, zinc, lead, mercury). It is hoped that a pollution monitoring system might be developed from this work.

Proteins and Protein Engineering

The latest advances in biochemistry have made it possible to begin to build proteins from scratch, and so in principle create a molecule to do a specific task. Because it is the structure of the protein which controls its function very precise information about thestructure is essential and high-resolution NMR is one of the few ways of uncovering it. The NMR spectra reveal information about the neighboring atoms for each atom in the molecule. With even a small protein containing hundreds of atoms one of the major problems is too much information. The spectroscopist can design the NMR experiment to keep the amount of information to a manageable level, and then molecular modelling computer programs are used to generate three-dimensional structures from the NMR data. Such research programs have for instance been applied in the development of new antibiotics and x-ray and magnetic resonance contrast agents.

Computer Applications and Pattern Recognition Techniques

With manifold tissue parameters, magnetic resonance imaging (MRI) has a great variety of image contrast and substantial theoretical potential for tissue discrimination and even characterization in different organs. This, on the one hand, is a major advantage of MRI compared with other imaging modalities, on the other hand, it may prove to be disadvantageous because several series of images with different parameter weighting (i.e. proton density-, T1, and T2-weighting, pre- and post-contrast) of the same region of the body have to be acquired. This leads to several dozen images per examination which have to be read by the radiologist. Image reading and interpretation is basically done as (a) analysis of morphology, and (b) analysis of signal behavior. In general, MRI is a qualitative and subjective examination with a high level of uncertainty.

For routine clinical imaging, a simplification of the diagnostic procedure would be advantageous. This would both cut down time and costs, as well as diagnostic uncertainty. In addition, pattern recognition techniques could lead to a preliminary diagnosis before images are read and increase diagnostic performance. Tissue discrimination and characterization on the basis of relaxation time calculations has been shown to be unfeasible. Thus, other methods have to be considered. Basic considerations must include: (a) MRI possesses several physical parameters; (b) there are difficulties in computing and exploiting these parameters; and (c) there is the possibility to devise a multivariate test (pattern recognition techniques), which will decrease the level of uncertainty in the diagnosis and increase the diagnostic performance.

In general, MR images are crude and it is inappropriate to process them by pattern recognition techniques, mainly because of geometrical distortion, intensity distortion, and noise. However, first results have demonstrated that computers can recognize certain normal structures and distinguish them from pathology. These methods could also be applied to industrial use of MRI or other imaging techniques, e.g. for quality assurance programs.

Non-Destructive Testing

Some applications of NMR in non-destructive testing have been described before, e.g. the examination of plastic and ceramic components. Here, a broad range of applications has been developed, but the spectrum of possible new applications is wide. Space technology will exploit the possibilities of NMR to assess the influence of microgravity, acceleration, and vibration upon materials and their possible degradation. Monitoring could be performed before and after space flights, and with suitable equipment even in space. Quality assurance programs with NMR include also measurement and control of other techniques such as chromatography. Small, robust NMR machines are already available, and machines for particular applications custom-tailored for specific technical solutions can be developed at competitive prices.

EMRF

The European Forum
for Magnetic Resonance Research and Application

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