WATR - water attenuation by transverse relaxation

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WATR - water attenuation by transverse relaxation.

With this technique water resonance can be reduced when T2 relaxation time of sample resonances is substantially longer than that of water. This experiment basically acts as a "T2 filter" against the water resonance.

The experiment is recorded using CPMG pulse sequence (or a sequence with inserted CPMG element for 2D experiments such as COSY and TOCSY) with a sufficient CPMG delay set for a complete relaxation of water resonance while still observing the spectrum of the sample.

For faster T2 relaxation of water reagents such as hydroxylamine (NH₂OH at ~200 mM [1]), ammonium chloride (NH₄Cl ~450 mM) and paramagnetic relaxation reagents can be added to the sample.

WATR technique allows observing resonances at water frequencies at the cost of attenuation brought by the total duration of the CPMG sequence of about 300 ms. Such delay permits observation of small molecules with M_r < 1,000 Da.

References

1. Larive, CK and Rabenstein, DL. Two-dimensional 1H NMR spectroscopy of aqueous solutions with elimination of the water resonance by transverse relaxation: Application to assignment of the 1H NMR spectrum of reduced arginine vasopressin. Magnetic Resonance in Chemistry 29(5), 1991. BibTeX [vasopressin]