NMR Instrumentation ppt Magnet Permanent and conventional electromagnets The Magnetic Field Sweep Sweep Generator frequency sweep method field sweep method The Sample Holder The Sample Probe Radio Frequency Generator Oscillator Radio Frequency Receiver Amplifier The Signal Detector and Recording System NMR Instrumentation ppt Magnet Permanent and conventional electromagnets The Magnetic Field Sweep Sweep Generator frequency sweep method field sweep method The Sample Holder The Sample Probe Radio Frequency Generator Oscillator Radio Frequency Receiver Amplifier The Signal Detector and Recording System

1. NMR INSTRUMENTATION
Presented by:
Aditya Sharma
M.S. (Pharm)
Pharmaceutical Analysis
NIPER Guwahati

2. Magnet:
 It is used to supply principal part of the field H.
The magnet should give homogenous magnetic
field.
 Strength of the magnetic field is high, at least
20,000 gausses because the chemical shifts are
proportional to the field strength.
 Two factors are important in the design of
magnets: i. homogeneity or uniformity of the field
and constancy of the field strength and ii.
maximum obtainable strength of the field.
 Permanent and conventional electromagnets are
generally used in spectrometers operating upto
100 MHz to 230 MHz.

3. The Magnetic Field Sweep
 An alteration over a small range in the applied field may be made by making
use of a pair of coils (Helmholtz coils) located parallel to the magnet face.
 The field strength is changed automatically and linearly with time and this
change is synchronized with the linear device or a chart recorder.

4. Sweep Generator:
 In order for a nucleus to resonate, the precession frequency should be equal
with that of applied field or Rf radiation. This can be achieved by:
a. Frequency Sweep Method: This method is used to resonate the nucleus. The
frequency of the Rf radiation is changed so that it becomes equal to resonance
frequency or precession frequency.
b. Field Sweep Method: In this method, to resonate the nucleus, the frequency of
the Rf radiation is kept constant and the precession frequency is changed by
changing the applied magnetic field. It is better because it is easier to vary the H0
than Rf radiation.

5. The Sample Holder:
 A usual NMR sample cell consists of a 7.5 cm +- 0.3 cm in diameter. The sample
holder should be chemically inert, durable and transparent to Rf radiation.
Generally, the glass tubes are sturdy, practicable and cheap. The sample must
be in the liquid or solution state for high resolution spectra.

6. The Sample Probe:
 It is a device that holds the sample tube in a
fixed position in the field and it is also
provided with an air driven turbine for
rotating the sample tube along its
longitudinal axis at several hundred RPM.
 It is used to excite and detect the
magnetization in radio-frequency of
sample.
 The most essential component is the Rf
transmitting and receiving coil.
 For maximum sensitivity, a fixed radio probe
is needed.

7. Radio Frequency Generator:
 To generate radio frequency, radio frequency generator is used. A fixed
oscillator having a capacity of exactly 60 MHz is normally used.
 The maximum interaction of the Rf radiation with the sample, the coil of
oscillator is wound around the sample container.
 The coil is wound perpendicular to the applied magnetic field.

8. Radio Frequency Receiver:
 When the radio frequency radiation is passed through the magnetized sample,
two phenomena, namely absorption and dispersion may occur.
 The detector should be capable of separating absorption signal from dispersion
signal and from that of Rf oscillator.
 There are two main methods of detection: First method uses a radio frequency
bridge and Second method employs a separate receiver coil.

9. The Signal Detector and Recording
System:
 The coil has been used to direct the radio frequency signal produced by the
resonating nuclei. The electrical signal generated into the coil must be amplified
before it is recorded.