PULSE TECHNIQUES AND FOURIER TRANSFORMS - FTNMR SPECTROSCOPY

                       

If we can could stimulating all transitions within the nuclear spin states are would be arise, but the excitation would required a mere fraction of a second to execute. This is precisely what is done in pulsed NMR :, for proton nmr spectroscopy, the sample is irradiated at fixed fields, with a strongest pulse of radiofrequency is energy containing all the frequencies over the  ¹H  range, For example, frequency is spread arrounding with 60 MHz at 1.4 T   The protons in each environment absorbed their appropriate frequencies from the pulse, and these frequencies couple to giving beats.

                                         The presentation at the figure is an " interferogram"   in the time domain and it's Fourier Transform renders that the same information in the frequency domains. For this reason the technique of pulsed nmr spectroscopy is usually called pulsed FTNMR or simply FTNMR, Thus distinguishing from the continuous waves NMR, and  CWNMR.

                                     This pulse duration is may be approximately ( 10μs), and when it's switched off, the nuclei undergo relaxation process and reemit the absorbed energies. The instrumental problem is that the all these reemitted energies are emitting simultaneously as a complex interacting pattern of reemitted decay signals :, this output is digitized in a computer monitor, and each individual frequency is identifies from the interference pattern by the mathematics of Fourier Transforms. Each frequency is plotting on a linear frequency scale - the nmr spectroscopy. 

Above the figure :, exponential decay from all nuclei undergoing relaxation and consists of composite of several individual frequencies, which can be separated and presented on a linear frequency scale. 

ADVANTAGES OF FTNMR SPECTROSCOPY

1) The entire spectrum can be recorded and computerized and transformed in a few of seconds.

2)                it's able to work,      at too very low                 cconcentration, especially in biological organic chemistry.         

3) it's able to record easily and excellent spectra from the ordinary organic molecules containing low natural abundance of            ¹³C   nuclei, etc....