Pulse Sequences as Combination of Building Blocks

It is not possible to describe the basic experiment structure of one dimensional and n dimensional experiments using a single scheme but they may be described using three 

The processes that occur during the evolution period are probably the most important in describing the effect of the complete pulse sequence. During this period coherence can evolve, coherence can be selectively manipulated or coherence transfer can occur. Coherence manipulation can be the inversion of the coherence order (WATERGATE experiment) or in a l S spin system a phase shift depending upon signal multiplicity (APT or SEMUT experiment). In the case of heteronuclear IS spin systems the creation of antiphase coherence and subsequent polarization transfer using a INEPT or a DEPT unit can be used in multiplicity edited experiments or heteronuclear 2D correlation experiments. In transient NOE experiments such as ROE and TROESY, coherence 

The modulation part is the main part to create n dimensional experiments. During this period coherences evolve under free precession due to the chemical shift or coupling of a particular kind of nucleus like nucleus in an IH, COSY experiment. If only chemical shift evolution is allowed a shift resolved COSY spectrum results whilst a J-resolved experiments is obtained if only coupling evolution is permitted. Incrementing the delay between experiments modulates this evolution which after Fourier transformation generates the second frequency dimension. In a further step several modulation units can be implemented to create n dimensional spectra where each dimension is assigned to an individual nucleus or a particular type of coupling. 

Initially the detection period might appear as the least important part of the pulse sequence. However for nD experiments the selection of the appropriate detection mode can have a significant effect on the experiment sensitivity thus the magnitude detection mode results in broad signals which compared to spectra recorded using phase-sensitive detection, have a lower signal-to-noise ratio and resolution. 

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