FOURIER-

TRANSFORM

NUCLEAR

MAGNETIC

RESONANCE

(FT-NMR)

PRESENTED BY,

Anjali.c

I year m.pharm

Dept. Of pharmacy practice

Grace college of pharmacy

FOURIER-TRANSFORM

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).

FT-NMR

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

FT-NMR INSTRUMENTATION

COMPONENTS OF FT-NMR 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.

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.

ADVANTAGES OF FT-NMR 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.