70 Years of Magnetic Resonance: From the Physical Experiment to an Indispensable Tool

The first successful experiment with magnetic resonance was performed in Kasan using EPR in 1944. In 1946, the first NMR signals were detected in parallel at Stanford University and Harvard University. After these discoveries, the physical experiments developed very rapidly in numerous laboratories throughout the world and by the mid fifties, almost all of the physical properties had been described. In a discussion around this time, a physicist declared: “the interest in NMR is gone as I expect nothing new!” But in 1950, a new feature was found: the chemical shift. This was the basic property of the NMR experiment that chemist needed and thus, the NMR story started from scratch.

Varian was the first commercial company that realized the potential of this new method and designed an analytical NMR system working at a frequency of 30 MHz. The general acceptance of the new method as an analytical tool became a reality with the introduction of the Varian A 60 for routine proton spectroscopy. At the same time, Bruker, a new company in the field, introduced the first commercial pulsed instrument. The experimental requirements grew fast with requests for new methods and other nuclei. The Bruker HFX Series, introduced in 1967 with its 3 channel concept, met these requirements which opened up many new NMR applications.

In the early sixties, Richard Ernst developed a method for processing utilizing the Fourier transformation (FT) but real applications only became available with the introduction of a system with an integrated computer by Bruker in 1969. This system included both proton and hetero nuclei, especially C13. The introduction of the Bruker WH Series 3 years later was the first instrument dedicated to FT and became the forerunner of modern NMR technology.

The trend to higher magnet field strength was limited with iron magnet systems operating up to 100 MHz. In the late sixties, Varian began developing a magnet using superconducting wire operating at 220 MHz. This instrument was for limited applications only. Oxford University, Oxford Instruments and Bruker, together developed magnets using a new approach, leading to versatile systems operating at 270 MHz. Over the years, improved superconducting wire and magnet technology allowed for an increase in the operating frequency up to 1000 MHz and the race for even higher frequencies is not over. Today ease of use and cost of operation is another aspect of great importance in magnet development.

The late seventies saw the introduction of multidimensional spectroscopy and MR imaging. Structure elucidation on proteins and hole body imaging where only two of the methods now possible. Automation increased sample throughput and therefore broadened the areas of applications. These new methods required higher stabilities and higher sensitivity. The step to new digital concepts and the introduction of cryogenic cooled probe heads improved NMR performance significantly and made operation easier and more automated. This new performance level opened additional application possibilities. One of the most significant is the analysis of complex mixtures, like body fluids, fruit juices, wine and tissue (with MAS). These methods are fast, need almost no sample preparation and give direct results with the appropriate data banks.

Magnetic resonance is approaching its eighth decade and is as challenging as ever but has enormous potential applications for research in the future.