th  - 1987 - 51st ENC Conference

WK28
SELECTION OF COHERENCE TRANSFER PATHWAYS BY FOURIER ANALYSIS
HOW TO IMPROVE THE EFFICIENCY OF 2D NMR SPECTROSCOPY
R. Ramachandran, P. Darba and L.R. Brown*
Research School of Chemistry
The Australian National University
Canberra, A.C.T. 2601, Australia
To interpret complex 2D NffR spectra it is often necessary to run
a series of complementary 2D N~ spectra which select for different
kinds of information. Examples would be a series of auto correlated
spectra with filters of different quantum orders or a series of
multiple quantum correlation spectra of different quantum orders. As
currently practiced, each member of the series is recorded separately
using concurrent cycling of pulse and receiver phases to select the
appropriate coherence transfer pathway. This is a very inefficient
procedure which requires large amounts of spectrometer time and which
leads to spectra that may not be strictly comparable due to
instability of the spectrometer and/or the sample.
A method will be shown for extracting such a series of spectra
from a single data set. The new method involves recording a series
of spectra with appropriate incrementation of pulse phases, but with
no variation of receiver phase. Fourier analysis of the set of
spectra by means of digital zero-order phase corrections then allows
extraction of coherence transfer pathways containing any specific
multiple quantum order from the same data set. Examples will be
given for generation from a single data set of multiple quantum
filtered COSY spectra of different quantum orders and multiple
quantum spectra of different quantum orders.
A major advantage of the proposed method is that every transient
recorded is used in the generation of the spectum corresponding to
each quantum order. This means, for example, that compared to
recording a COSY spectrum with a two-quantum filter by conventional
means, there is no penalty in sensitivity involved in generation of
multiple quantum filtered spectra with filters of order 2,3 and 4 (or
more) by the proposed method. This also makes the new method highly
efficient for experiments which require co-addition of spectra
corresponding to different quantum orders, e.g.E. COSY or time
reversal. An example will be shown for E. COSY.