Water Suppression
Removal of H2O is critical when observing samples in 90 or 100% H2O. The most common method is called excitation sculpting, which can reduce the water signal by up to 10,000 or more. For when labile protons must be observed, there is a "flip-back" version that preserves their signal, even when they are exchanging with the suppressed water signal.
PURGE (Pre-saturation Utilizing Relaxation Gradients and Echoes) is another (pre-saturation) solvent suppression technique. The technique is simple to set up and requires only the solvent frequency and pre-saturation power to be adjusted. It displays high selectivity, good phase properties, and flat baselines. It can be run with a minimum of 4 scans and combined with other multidimensional techniques such as TOCSY. Components may be filtered based on their T2 values. As with other pre-saturation techniques, exchangeable protons such as amides will show reduced intensity when suppressing water.
Shown below are an un-suppressed proton spectrum and a PURGE spectrum of a 2mM sucrose sample dissolved in 90% H2O, 10% D2O at 400 MHz.
