Adiabatic 1H decoupling scheme for accurate intensity measurements in 13C NMR

Adiabatic proton decoupling has been optimized in order to obtain accurate quantitative measurements of intensities on C-13 NMR spectra. For each offset, the minimum adiabaticity factor (Km) reached during the pulse was computed. This K-m profile was used to optimize the peak value and the swept frequency range of the adiabatic pulses. With a cosinus amplitude modulation, offset-independent-adiabaticity, and the M4P5-M4P9-M4P5'-M4P9' phase cycle, an accuracy of 2 parts per thousand for the C-13 NMR measurements was reached. An approach using bi-labeled C-13 acetic acid and ethanol at 99% allowed a fine experimental determination of the uniformity of the decoupling profile. The comparison with WALTZ-16 highlights the improvements in the uniformity of the proton decoupling. (c) 2006 Elsevier Inc. All rights reserved.