Recording and Simulation of 2D Experiments

This section examines some of the general experiment parameters required to create a 2D data matrix and the special experiment setup in NMR-SIM. The most important experimental parameters are inO, NS, delays di and the type of quadrature detection in fl. The user-related entries for the experiment setup are  

In a 2D experiments a series of FIDs are acquired using an incremented delay tl to build up a 2D data matrix, each row of the matrix corresponding to a specific value of tl. The effect of the incremented delay is to modulate the FIDs from the experiments, which can be interpreted and analysed as a pseudo FID with respect to the time delay tl. By convention the incremented delay is called dO and the increment inO. The detected frequency range in the fl dimension is given by ASW [Hz] = l/(inO ndO ). Normally there is only one time increment variable but in special pulse sequences based upon for instance the ACCORDION-principle, see section 5.9.3, additional increment variable ini, in2... can be defined. Usually for the first experiment dO = 3 us and for the second and subsequent experiments dO = 3u -i- inO (n -1). In a number of 2D experiments the 

NMR-SIM does not differentiate Co-Addition, TPPI and States-TPPI concerning ndO, but the sweep width has to be calculated correspondingly to Table 3.2. In NMR-SIM for homonuclear 2D experiments with SW(fl) = SW(f2) the calculation of inO is extremely simple, the sweep width SW is entered in the inO field and the value calculated by an internal algorithm based on equation [3-11]. This procedure is illustrated in Check it 3.3.1.1. 

One further difference between the two frequency dimensions of a 2D spectrum should be mentioned. In contrast to direct acquisition in t2 no filters (analogue or digital) can be applied in the tl dimension. As a consequence signals outside of the fl spectral limits are folded back and give rise to ghost peaks in the 2D spectrum. To prevent this occurring in either the f 1 spectral width and observation frequency have to be adjusted or a more sophisticated pulse sequence with region selective pulses in fl has to be used. NMR-SIM can also produce folded peaks in the fl dimension as demonstrated in Check it 3.3.1.2. 

In Check it 3.3.1.3 the explicit calculation of the inO increment is demonstrated using equation [3-11] for two different quadrature detection modes. 

---