Pulse sequence COSY-90 modification

Fiffire 5.38 Pulse sequence for delayed COSY—a modification of the COSY experiment. The fixed delays at the end of the evolution period t and before the acquisition period <2 allow the detection of long-range couplings between protons. 

With suitable modification of the pulse sequences the para-hydrogen effect can be used to enhance the signals in many NMR experiments, for example, COSY, HMQC, HSQC, EXSY and Overhauser spectroscopy. ... 

This difficulty is neatly side-stepped by a modification called double quantum filtered COSY (DQF COSY). The pulse sequence is shown opposite. 

A common modification of the basic COSY sequence is one in which the 90° mixing pulse is replaced with one of shorter tip angle, P, usually of 45 or 60 degrees (Fig. 5.52). These experiments are typically acquired and presented as absolute-value experiments since, strictly speaking, the use of a pulse angle less than 90° does not produce purely amplitude-modulated data. 

Analysis of COSY spectra started with the paper by Bax and Freeman who discussed the potential of the Teener s experiment . A modification, later called COSY-45, is introduced for the observation of the relative sign of coupling constants in triangularly coupled spin systems. This kind of multiplet structure prompted the development of specific sequences in order to extract a certain kind of coupling constant information and coupling network. Another modification involves the use of selective pulses giving rise to spectra that are simplified in... 

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