IMPROVEMENT IN QUANTITATIVE ACCURACY OF ¹³C DEPT INTEGRALS BY PARAMETER-OPTIMIZATION

ABSTRACT

The polarization transfer method DEPT (Distortionless Enhancement by Polarization Transfer) has been optimized to improve quantitative ¹³C NMR measurements. The major drawback of the DEPT sequence is its sensitivity to deviations of pulse flip angles from their ideal values, because of inhomogeneity of the RF field or simply because of maladjusted pulse lengths. To overcome this inadequacy, we have matched the multi-pulse sequence DEPT to reduce this dependence. We have analysed theoretically and experimentally the signal intensity in terms of evolution periods, frequency offsets and RF pulse flip angles. The conditions for quantitative acquisition were optimized by introducing composite pulses and by modifying the phase cycle. After these modifications, the accuracy of measurements performed with the developed DEPT method was of the same order as that obtained with one-pulse acquisition with an improved signal-to-noise ratio.

Keywords:

• DEPT
• Quantitative
• ¹³C NMR
• Pulse imperfections

ACKNOWLEDGMENTS

The authors thank R. Robins for critical comments on the manuscript. The contribution of the Scientific Council of the Pays de la Loire Region to the purchase of a 500 MHz NMR spectrometer is gratefully acknowledged. N. Karabulut is grateful to the MENRT for a graduate bursarry.