TY - JOUR

T1 - Improved background suppression in H-1 MAS NMR using composite pulses

AU - Odedra, Smita

AU - Wimperis, Stephen

PY - 2012/8

Y1 - 2012/8

N2 - A well known feature of H-1 MAS NMR spectroscopy, particularly of solids where the concentration of H-1 nuclei is low, is the presence in the spectrum of a significant broad "background" signal arising from H-1 nuclei that are outside the MAS rotor and radiofrequency coil, probably located on the surfaces of the static components of the probehead. A popular method of suppressing this unwanted signal is the "depth pulse" method, consisting of a 90 degrees pulse followed by one or two 180 degrees pulses that are phase cycled according to the "Exorcycle" scheme, which removes signal associated with imperfect 180 degrees pulses. Consequently, only spins in the centre of the radiofrequency coil contribute to the H-1 MAS spectrum, while those experiencing a low B-1 field outside the coil are suppressed. Although very effective at removing background signal from the spectrum, one drawback with this approach is that significant loss of the desired signal from the sample also occurs. Here we investigate the H-1 background suppression problem and, in particular, the use of novel antisymmetric passband composite pulses to replace the simple pulses in a depth pulse experiment. We show that it is possible to improve the intensity of the H-1 signals of interest while still maintaining effective background suppression. We expect that these results will be relevant to H-1 MAS NMR studies of, for example, nominally perdeuterated biological samples or nominally anhydrous inorganic materials. (C) 2012 Elsevier Inc. All rights reserved.

AB - A well known feature of H-1 MAS NMR spectroscopy, particularly of solids where the concentration of H-1 nuclei is low, is the presence in the spectrum of a significant broad "background" signal arising from H-1 nuclei that are outside the MAS rotor and radiofrequency coil, probably located on the surfaces of the static components of the probehead. A popular method of suppressing this unwanted signal is the "depth pulse" method, consisting of a 90 degrees pulse followed by one or two 180 degrees pulses that are phase cycled according to the "Exorcycle" scheme, which removes signal associated with imperfect 180 degrees pulses. Consequently, only spins in the centre of the radiofrequency coil contribute to the H-1 MAS spectrum, while those experiencing a low B-1 field outside the coil are suppressed. Although very effective at removing background signal from the spectrum, one drawback with this approach is that significant loss of the desired signal from the sample also occurs. Here we investigate the H-1 background suppression problem and, in particular, the use of novel antisymmetric passband composite pulses to replace the simple pulses in a depth pulse experiment. We show that it is possible to improve the intensity of the H-1 signals of interest while still maintaining effective background suppression. We expect that these results will be relevant to H-1 MAS NMR studies of, for example, nominally perdeuterated biological samples or nominally anhydrous inorganic materials. (C) 2012 Elsevier Inc. All rights reserved.

KW - H-1 MAS NMR

KW - Background suppression

KW - Depth pulses

KW - Composite pulses

KW - BAND POPULATION-INVERSION

KW - BROAD-BAND

KW - RADIOFREQUENCY PULSE

KW - REFOCUSING PULSES

KW - ITERATIVE SCHEMES

KW - SOLID-STATE

KW - NARROW-BAND

KW - EXCITATION

KW - SPECTROSCOPY

KW - SEQUENCES

U2 - 10.1016/j.jmr.2012.05.010

DO - 10.1016/j.jmr.2012.05.010

M3 - Journal article

VL - 221

SP - 41

EP - 50

JO - Journal of Magnetic Resonance

JF - Journal of Magnetic Resonance

SN - 1090-7807

ER -