![]() ![]() bbb p = 0 abb bba bab p = 1 p = 2 aba aab baa p = 3 aaaģ Multiple quantum filtered COSY (MQF-COSY)įor example, the CTP for selecting double-quantum coherence or higher is: Although we may have single-quantum coherence, it is not affected by the second/third pulses. We can add a pulse (with proper phasing) such that only double- or higher quantum transitions selected by the first and second pulses will end up in the p = -1 line. This is extremely useful to discard certain signals in COSY spectra. However, if we think of the right phase cycle, we can design a CTP so that only coherence corresponding to transitions of a certain order will be detected by the receiver. In a three-spin J-coupled system we have: The big problem is that we can only study the evolution of single-quantum transitions with our vector representation. We’ve been saying for a while now that in a coupled spin system there are zero- (p = 0), single- (p = 1), double- (p = 2), etc-quantum transitions. We also said that we analyze changes in coherence with CTPs, in which we only jot down what we want to detect at the end of the whole experiment. They are basically the same, because they come from the same mathematical description (the ‘operators’ used to determine what happens with coherence after pulses work the same way…). ![]() There are some things worth remembering: The phase shift acquired by a certain coherence will depend on the change in coherence order associated with it (Dp) and the phase of the pulse that creates it (f): In order to select a coherence pathway, the pulse (or receiver) that we are using to select it has to have a phase such that: were f is the phase of the pulse that created it. 1 More coherence… Last time we saw (or at least tried) that we can select certain orders of coherence by cycling the phases of a pulse sequence appropriately. ![]()
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