Solvent suppression pulsed field gradients

Wolfender et ah, and this coupled technique is treated more comprehensively in Chapter 1. The LC-NMR technique is by nature rather insensitive however, high-field magnets and recent improvements in solvent suppression, pulse field gradients, and probe technology have made it possible to achieve useful results on various flavonoid struc-tures. The detection limit with a 60 p.1 cell in a 500 MHz instrument for a compound with a molecular weight of around 400 amu may typically be around 20 p.g, and the information provided is hitherto mainly based on NMR spectra or correlation experiments. 

The use of actively shielded magnetic field gradients has made the use of pulsed field gradients possible. The use of pulsed field gradients reduces experiment time, minimizes artifacts, and allows for further solvent suppression. 

Selective probe heads are used for optimal sensitivity for a particular nucleus. Sensitivity of a selective H probe head is normally greater than that of a switchable probe head with indirect observation. With a selective X-nucleus (a nucleus other than proton) probe head, decoupling of protons is normally possible. Because of their limited usefulness, selective probe heads are rare in NMR laboratories. Other probe heads are also available, for example, those for triple resonance experiments and experiments utilizing pulsed-field gradients. In addition to their suitability for 2-D experiments, the gradients are particularly suitable for solvent suppression (20). 

Dalvit C, Bohlen IM, Multiple-Solvent Suppression in Double-Quantum NMR Experiments with Magic Angle Pulsed Field Gradients, Magn. Reson. Chem., 34 829-833, 1996. 

C Dalvit, JM Bohlen. Multiple-solvent suppression in double-quantum NMR experiments with magic angle pulsed field gradients. Magn Reson Chem 34 829-833. 1996. 

Fig. 11. (A) A conceptual diagram of the WATERGATE subunit, the ir RF pulse is some type of selective tt pulse. (B) Multiple solvent suppression using the double-pulsed field gradient echo. Ihe selective ir pulses are SLP pulses to enable multiple solvent suppression. To avoid breakthrough of undesired coherences, different values for the gradients are used in the first and second echo. The phase cycling is given elsewhere. ...

The most effective approach to date to solvent suppression is the destruction of the net solvent magnetisation by pulsed field gradients (PFGs), so ensuring nothing of this remains observable immediately prior to acquisition. The... 

Figure 9.27. Solvent suppression schemes employing pulsed field gradients based on (a) WATERGATE (single-echo) and (b) excitation sculpting (double-echo) principles. The pulse element S has zero net effect on the solvent resonance but inverts all others.

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