Improvements in solvent-signal suppression

Abstract

Three recent improvements in solvent-signal suppression are described. First, PJR (“power-adapted jump and return”) replaces JR (jump and return). It goes beyond the “infinitely short π 2 pulse” approximation and can therefore be used even when the available RF power is low. The phase shift is small, and the amplitude correction providing a flat response is simple and power-independent. With a postexcitation delay, PJR generates an echo. Second, “modified binomials,” i.e., binomials sandwiched between two π pulses are studied. This simple modification eliminates the linear phase shift, which is the main problem of binomial sequences. It has a clear theoretical basis. These two sequences are applied to the observation of a test sample of thymidine, following a proposed standard procedure for the evaluation of methods of solvent-signal suppression. Third, it is pointed out that the elimination of radiation damping would avoid the resulting rotation of the magnetic moment during the RF-free intervals within solvent-signal-suppression excitation sequences. It may be achieved by incorporating the coil in an open, series-tuned, matching circuit.