2. It is the mathematical operation in which the
complex waveform can be broken-down into
simple mathematical operations.
It is the mathematical operation required to
convert a time domain spectrum to frequency
domain spectrum (or vice versa).
3. FTNMR or pulse NMR, the sample is irradiated
periodically with brief, highly intense pulses of
radio- frequency radiation, following which the
free induction decay signal - a characteristic radio-
frequency emission signal stimulated by the
irradiation – is recorded as a function of time.
The frequency- domain spectrum can be obtained
by a Fourier transform employing a digital
computer
4.
5.
6. The central component of the instrument is a highly
stable magnet in which the sample is placed.
The sample is surrounded by the transmitter/receiver
coil.
A crystal controlled frequency synthesizer having an
output frequency of Vc - produces radio-frequency
radiation.
This signal passes into a pulse switch and power
amplifier, which creates an - intense and reproducible
pulse of RF current in the transmitter coil.
Resulting signal is picked up by the same coil which
now serves a as - receiver.
7. The signal is then amplified and transmitted to a
phase sensitive detector.
The detector circuitry produced the difference
between the nuclear signals Vn and the crystal
oscillator output Vc which leads to the low
frequency time-domain signal .
This signal is digitalized and collected in the
memory of the computer for analysis by a Fourier
transform program and other data analysis
software.
The output from this program is plotted giving a
frequency domain spectrum.
8. FT-NMR is more sensitive and can measure weaker
signals.
The pulsed FT-NMR is much faster (seconds instead of
min) as compared to continuous wave NMR.
FT-NMR can be obtained with less than 0.5 mg of
compound. This is important in the biological chemistry,
where only μg quantities of the material may be
available.
The FT method also gives improved spectra for sparingly
soluble compounds.
Pulsed FT-NMR is therefore especially suitable for the
examination of nuclei that are magnetic or very dilute
samples.
