Solvent signal suppression in NMR

The last four decades have seen a continuous evolution in suppression techniques that attempt to meet new and increasingly stringent requirements (e.g., lower solute concentration, multiple signals, and greater selectivity). Of particular concern at higher field strengths and with modern high sensitivity NMR probes is the greater severity of radiation damping. Although quite a few techniques have been developed for the suppression of radiation damping, easier pulse sequence based radiation damping suppression methods which are compatible with common solvent suppression schemes are required. Of all the pulse sequence suppression methods, the frequency differentiation based methods are the most versatile; and future developments will likely include the invention of novel frequency selective RF pulses with large excitation bandwidths, sharper null regions, and immunity to non-ideal conditions such as B0, B1, and T1 inhomogeneity as well as to the effects of radiation damping. The performance of suppression methods is often illustrated on (biomolecular) samples with relatively high concentrations (e.g., mMrange) under ideal conditions (e.g., starting from thermal equilibrium) while in reality the intended application is for samples at super low concentrations (e.g., 6 lM) as is commonly encountered, for example, ex vivo (e.g., NMR diffusion studies on peptide–membrane interactions); therefore, testing suppression performance on super low concentration samples under realistic conditions should become standard during the development of new suppression methods. As the availability of higher field clinical MRI equipment becomes more widespread in conjunction with the development of digitizers with higher resolution and more efficient methods for the suppression of sideband modulation; in vivo NMR experiments without water suppression will find more and more applications in medicine. This will also spur greater developments in post-acquisition data processing.