Improvements in Solvent-Signal Suppression

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 π2 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.