GB1191455A - Improvements relating to Nuclear Magnetic Resonance Spectroscopy. - Google Patents

Abstract

1,191,455. N.M.R. spectrometers. PERKINELMER Ltd. Aug. 16, 1967 [June 1, 1966], No. 24396/66. Heading G1N. In an N.M.R. spectrometer, spin-coupled gyromagnetic nuclei are discoupled by subjecting the sample to decoupling R. F. power which is arranged to saturate all resonances over a conventionally wide region of the N. M. R. spectrum while leaving unaffected a middle zone or "quiet slot" extending between convenient limits equidistant from the position on the spectrum corresponding to the frequency of the normal R. F. power applied to the sample, whereby as the sample is scanned in either the frequency scan or field scan mode the "quiet slot" flanked by saturated zones travels along the horizontal axis of the spectrum to enable a resonance occuring in a chemical group of the N.M.R. sample to be observed substantially free from spin coupling as the mid-point of the "quiet slot" approaches the chemical shift at which said resonance occurs. Three alternative embodiments are described with reference to Fig. 1, in which circuits A, B, C are respectively connected to point P. In one embodiment, a series of blocking oscillators 1 and a weighting network 2 provide signals at spot frequencies of 15, 20, 25, 30 and 35 c/s of substantially equal amplitude which modulate through a suppressed-carrier modulator 3, 60 Mc/s power from source 4 forming part of an N.M.R. spectrometer comprising also a sample probe 7, alternators 6, 8 and a buffer amplifier 5. The arrangement is such that only the first-order sideband pair from each blocking oscillator is effective. The width of the "quiet slot" is adjustable by 5 c/s steps by switching on or off the appropriate blocking oscillators. In a second embodiment, a 5 c/s oscillator 9 and a harmonic generator 10 are used. In a third embodiment, a 300 c/s white noise band from 9À7 kc/s to 10 kc/s modulates the output of a 10 kc/s oscillator 13 through a suppressed-carrier modulator 14 and a low pass filter 15 passes only the 0-300 c/s sideband. An adjustable means 16 for increasing the frequency of oscillator 13 by an amount from 0 to 50 c/s provides a "quiet slot" of continuously adjustable width. The sample may contain an internal reference having a large chemical shift, e.g. trimethylsilane (T. M. S.) and the N.M.R. spectrum may be scanned between the limits of the chemical shift of a bare proton and the chemical shift of T. M.S.