FT-NMR spectrometry works by applying pulses of radio frequency energy to excite nuclei in a sample simultaneously, rather than continuously scanning individual frequencies. This allows the free induction decay signal to be recorded over time and converted to a frequency spectrum using Fourier transforms. FT-NMR provides higher sensitivity than continuous wave NMR, allowing analysis of smaller sample sizes, and faster acquisition of spectra in seconds rather than minutes. The technique was pioneered by Richard R. Ernst, who won the Nobel Prize in Chemistry in 1991 for his contributions to the development of FT-NMR and multi-dimensional NMR spectroscopy.

1. Assignment: FT-NMR Spectrometer
Submitted To:
Dr. Sara Musaddiq
Submitted By:
Sidra
Roll No:
MP.CHM.04
M.Phil Chemistry
THE WOMEN UNIVERSITY MULTAN
FT-NMR SPECTROMETER:

2. INTRODUCTION:

3. FOURIER-TRANSFORM (FT):
 It is the mathematical expression in which the complex waveform can be
broken down into simple mathematical operation.
 That expression required to convert time domain spectrum to frequency
domain spectrum and frequency domain spectrum to time domain
spectrum.
 Digital data must be transfer into the frequency data.

4. It is necessary to use computer for solving these complex equations.

5. FT-NMR Spectroscopy:
 FT-NMR 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 fourier transform
employing a digital computer.
 The spectral range is not scanned continuously.
 Stimulate all transitions simultaneously.
 Sample irradiated by a pulse of RF radiation containing all the frequencies
over the protium range.

6.  A method to collect an NMR spectrum in which pulse of radio frequency
energy is used to excite all nuclei of a particular isotopes (H-1,C-13 etc.) in
the molecule simultaneously.
 In FT-NMR instrument, the change in magnitude of energy is very small and
the sensitivity of instrument is less.
 In the spectrum having radio frequency pulse, the frequency irradiate and
nuclei returns back to thermal equilibrium in normal state.
 The interferometer i.e. time domain graph is intensity v/s time.
 The NMR spectrum i.e. frequency domain graph is intensity v/s frequency.
 This was introduced by ‘JEAN BAPTISE JOSEPH FOURIER’.

7. Time domain to frequency domain:

8. SENSTIVITY:
The signal induced in the receiver coil depends:
 On the size of polarization Mz to be converted into Mxy coherence by the
angle 90 pulse.
 On the signal induced in the receiver coil at detector, depending on the
magnetic moment of the nucleus detected and its precession frequency.
 Unfortunately the noise also grows with the frequency.

9. CHEMICAL SHIFT :
 Resonance frequencies of the same isotopes in different molecular
surroundings differ by several ppm. For resonance frequencies in the 100
MHz range these differences can be up to a few 1000 Hz. After creating the
Mxy coherence, each spin rotates with its own specific resonance
frequency w, slightly different from the B1 transmitter and receiver
frequency w0. In the rotating coordinate system, this corresponds to a
rotation with an off set frequency W = w - w0.

10. PRINCIPAL OF FT-NMR:
 A nuclei present in a static magnetic field and than kept it in an external
oscillating magnetic field and further applied pulse of radio frequency that
is relatable to its resonating frequency. So this nuclei absorbe some energy.
And act as little tops at their resonant frequency.
 Fourier transform spectrometer is more expensive than continuous wave
spectrometer since it must have fairly sophisticated electronics capable of
generating precise pulses and accurately receiving the complicated
transient.

12. FREE INDUCTION DECAY:
Relaxation by emitting
radiation: signal- Free
Induction Decay (FID).
FID signals contain the
vector-sum of the responses
from all the spins.
A mathematical process
called a Fourier transform is
used to convert the FID into
the NMR spectrum.

13. How to record FID signals ?
 The free induction decay signal can be recorded by radio receiver and a
computer in 1-2 seconds.
 Many free induction decay signals are received, then these signals are
averaged in few minutes.
 A computer then convert the averaged transient into a spectrum.

14. FT-NMR INSTRUMENTATION:

15. Component of FT-NMR instrument:
 The central component of the instrument is highly stable magnet in which
the sample is places.
I. The sample is surrounded by the transmitter/receiver coil.
II. A crystal controlled frequency synthesizer having an output frequency of
Vc that produces radio frequency radiation.
III. This signal pass through a pulse switch and power amplifier, which creates
an intense and reproducible pulse of RF current in the transmitter coil.
IV. Resulting signal is picked up by the same coil which now serve as a
receiver.

16.  The signal is than amplified and transmitter to phase sensitive detector.
 The detector circuitry produces 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.

17. Pulsed fourier transform spectrometer:
Transmittance technique do not show by a pulsed fourier transform
spectrometer. In the most general description of pulse FT spectrometry, a
sample is exposed to an energizing event which causes a periodic responses.
The frequency of the periodic response, as governed by the field conditions in
the spectrometer, is indicative of the measured properties of the analyte.
 Power of the RF pulse:
The intensity of the signal detected in pulsed NMR is a function of the power of
the RF pulse used for excitation. Relaxation process occur.
 Pulse duration and recycling time:
All processional frequencies within the effective band width of the pulse are
excited. The extent is inversely proportional to the duration of pulse in the time
domain. The broader the pulse spectral region , the shorter is the pulse.

18. Examples of pulsed fourier transform
spectrometry:
 Magnetic spectroscopy an RF pulse in a strong ambient magnetic field is
used as the energizing event this turns the magnetic particles at an angle
to the ambient field resulting in gyration. The gyrating spins then induce a
periodic current in a detector coil each spin exhibits a characteristic
frequency of gyration which reveals information about the analyte.
 In fourier transform mass spectrometry the energizing event is the injection
of the charged sample into the strong electromagnetic field of the
cyclotrons. These particles travel in circles inducing a current in a fixed coil
on one point in their circle.
 Each traveling particle exhibits a characteristic cyclotrons frequency field
ratio revealing the masses in the sample.

19. DETECTOR:
 Detects the decay of magnetization with respect to time.
 The FID corresponding to absorption of a single frequency spectrum is a
simple exponentially decaying sine wave.
 The FID, modulating by all the frequencies, consists of a set of interfering
wave form along with noise.
 FID related with time is called time domain spectrum.

20. Stationery forms of fourier transform
spectrometer:
 In addition to scanning form of fourier transform spectrometer, there are a
number of stationary or self- scanned forms. While the analysis of the
interferometric output is similar to that of the typical scanning
interferometer, significant differences apply as shown in the published
analyses some stationery forms retain the fellgett multiplex advantage, and
their use in the spectral region where spectral noise limit apply is similar to
the scanning forms of the FTS. In the photon-noise limited region, the
application of stationery interferometer is dictated by specific
consideration for the spectral region and the application.

21. Advantages of FT-NMR:
 FT-NMR is more sensitive and can measure weaker signals.
 The pulse FT-NMR is much faster (seconds instead of min) as compare 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 micro gram 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.

22. conclusion:
 FT method can be applied to many types of spectroscopy.
 In simple terms a short square pulse of a given ‘carrier’ frequency ‘contains’ a
range of frequencies center about the carrier frequency with the range of
excitation being inversely proportional to the pulse duration.
 Fortunately the development of the FT-NMR coincides with the development of
digital computers and fast fourier transform algorithms.
 FT-NMR widely used for C-13,P-31and F-19 giving rapid scanning.
 The spectrum can be obtained with small (less than 5 mg ) of sample.
Noble prize:
Richard R. Ernst was one of the pioneers of pulse FT-NMR and won a noble prize in
chemistry in 1991 for his work on FT-NMR and his development of multi-dimensional
NMR.