Introduction

Nuclear MR (NMR) spectroscopy in bulk matter was demonstrated for the first time in 1945 when Bloch and Purcell independently demonstrated that a strong magnetic field induced splitting of the energy levels and detected the resonance phenomena (Bloch, 1946; Purcell et al., 1946). The method was originally of interest only to physicists for the measurement of gyromagnetic ratios (γ) of different nuclei, a constant specific to a particular nucleus, but applications of NMR to chemistry became apparent after the discovery of chemical shift and spin-spin coupling effects in 1950 and 1951, respectively (Proctor and Yu, 1950; Gutowsky et al., 1951). The spectra of high-resolution liquid NMR contain fine structure information because the nuclear resonance frequency is influenced by both neighboring nuclei and the chemical environment which allows information on the structure of the molecule to be deduced. Hence, NMR spectroscopy rapidly became an important, and widely used, technique for chemical analysis and structure elucidation of chemical and biological compounds.

Major technical advances in the 1960s included the introduction of superconducting magnets (1965), which were very stable and allowed higher field strengths than with conventional electromagnets to be attained, and in 1966 the use of the Fourier transform (FT) for signal processing. In nearly all contemporary spectrometers, the sample is subjected to periodic radio frequency (RF) pulses directed perpendicular to the external field and the signal is Fourier transformed to give a spectrum in the frequency domain.