The Transferred Nuclear Overhauser Effect trNOE

However, no comparison of the interaction strengths can be made between analytes 6 and 7 since the trNOEs were measured between different atoms. The intramolecular distance (r) is proportional to the NOE with an r dependence, and therefore different magnitudes of NOE will be observed if r differs between the molecules. For a valid comparison, it is important to know that the intramolecular distances between the groups giving rise to the trNOE cross-peak are the same. Therefore, this technique is well-suited for chiral discrimination studies. 

Analytes (chosen cross-peal Cross-peak intensity in the presence of phase A Cross-peak intensity in the presence cf phase B  

Phase Analyte MeOH MeOH MeOH MeOH MeOH 

It can easily be seen that the NOE cross-peak magnitude will reflect the retention order when a mobile phase composed of water/acetonitrile is used. An interesting increase in interaction strength is observed when the water concentration is reduced from 10% to 0% this is believed to reflect a change in retention mechanism from a hydrophobic dominated one, at water contents above 10%, to a hydrogen-bonding dominated one, at water contents below 10%. 

The Tj relaxation time for protons, measured using an inversion-recovery pulse sequence, is known to be shorter when the number of relaxation pathways is increased. This means that if an analyte proton is in closer proximity to one selector compared to another, this should be reflected in a shorter Tj relaxation time. Therefore, suspended-state HR/MAS Tj relaxation measurements can be used to map differences in proximities between analytes and chromatographic sorbents. 

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