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Precise measurement of (1)H 90 degrees pulse in solid-state NMR spectroscopy for complex and heterogeneous molecular systems.

Conte P, Piccolo A

Dipartimento di Ingegneria e Tecnologie Agro-Forestali (DITAF), Università di Palermo, Viale delle Scienze 13, 90128 Palermo, Italy. pellegrino.conte@unipa.it

The 90 degrees pulse calibration is essential in NMR spectroscopy to prevent artefacts in the liquid state or to enhance cross-polarization efficiency in the solid state. We verified pulse-angle (PA) errors due to circuit impedances in solid-state NMR and suggested a possible solution to prevent the inconvenience of PA errors. The classic pulse sequences used to calibrate (1)H 90 degrees pulse lengths by direct detection of protons or by cross-polarization were modified in order to replace single (1)H pulses with (1)H pulse trains. Pulse trains were found to decrease the effect of PA imperfections in the calibration of basic pulses (i.e. 90 degrees and 180 degrees ) for a number of organic substrates. The modified sequences are especially important to rapidly obtain pulse calibration of complex and heterogeneous molecular systems such as humic substances, which usually require a long time when using single (1)H pulses.

Published 22 March 2007 in Anal Bioanal Chem, 387(8): 2903-9.
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