Question

36.  Draw the pulse, etc. timing sequence for a one-dimensional, basic FT NMR spectral data collection.  Label each segment and describe briefly what happens during each time period.  (30 points)

Answer 1

Basic 1D NMR pulse sequence:

A pulse sequence is a visual representation of the pulse and relaxation delay used in the NMR experiment. There may be several pulse in a NMR experiment. Hoever the most basic NMR experiment has only one pulse. A basic 1D-NMR pulse sequence is shown below in figure 1.

Observed channel Relaxation delay time. Acquisition Figure -l

Relaxation delay: The sequence starts with a period of time known as relaxation time which will allow magnetic equilibriuum to achieve.

90o Pulse : A hard radiofrequency pulse will excite the nucleus transefering the magnetization vector into X,Y -plane. Schematically it is shown in the figure 2.

Bo Figure 2: Schematic representation of - a 90° pulse.

Acquisition time: When the nuclei starts relaxing towards the equilibrium then emit radiofrequency signal known as free induced decay(FID). Such sequence will only relate a sigle type of nuclei such as a 1H nuclei . The FID is detected in the observed channel in the experiment which is processed to get the spectrum.