ABSTRACT
LC-NMR spectra typically contain mobile-phase deuterated solvents that have significant amounts of proteosolvent. Because these solvent signals are large relative to the peaks of interest, the solvent signals need to be suppressed. Solvent suppression is required to address dynamic-range issues that prevent observation of the resonances arising from the compounds of interest. A number of solvent-suppression techniques were invented for this purpose. These solvent-suppression techniques include the standard presaturation [1] as well as binomial sequences such as 1331 [2, 3], or 11 or 121 [4]. The binomial sequence 1331 is a very efficient sequence for obtaining proton NMR spectra of dilute solutes in H2O. This sequence has been shown to suppress an intense water resonance by more than three orders of magnitude. The 1331 sequence consists of short, strong radio-frequency (RF) pulses designed to be insensitive to many of the imperfections of the NMR spectrometers. This sequence enables high-quality spectra to be acquired without the need for fine adjustment of pulse lengths, phase shifts, delays, and transmitter frequency. The numbers in the 1331 sequence give the relative pulse lengths. The overbars denote a 180° phaseshifted pulse, and equal delays exist between the pulses.
