Nmr instrumentation NAVEEN BALAJI

1. INSTRUMENTATION OF NMR
SPECTROSCOPY
Presented by:
NAVEEN BALAJI
1st M-Pharm
Department of Pharmaceutics
Sree Siddaganga college of pharmacy
Tumakuru.
Under guidance of:
Dr. M.S.CHAITANYA ,M.Pharm, Ph.D.,
Professor & HOD
Department of Quality Assurance
Sree Siddaganga college of pharmacy
Tumakuru.
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2. NMR SPECTROMETER
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3. NMR SPECTROMETER :-
• NMR Spectrometer is an instrument which is
used to obtain NMR Spectra.
• A high resolution spectrometer contains a complex
collection of electronic equipments.
• NMR spectrometers are referred to as 300 MHz
instruments (or) 500 MHz instruments, depending
upon the frequency of the RF radiation used for
resonance.
• These spectrometers use very powerful magnets to
create a small but measurable energy difference
between two possible spin states.
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4. • Protons in different environments absorb at
different frequencies, so that they are
distinguishable by NMR.
• The frequency at which a particular proton absorbs
is determined by its electronic environment.
• Modern NMR spectrometers use a constant
magnetic field strength, and then narrow range of
frequencies are applied to achieve the resonance of
all protons.
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5. NMR SIGNAL
BLOCK DIAGRAM OF NMR SPECTROMETER

6. COMPONENTS OF NMR
SPECTROMETER
 Magnet
 Field Lock
 Shim Coils
 Probe Unit
Sample Holder
RF Oscillator
Sweep Generator
RF Receiver
 Detector
 Amplifier & Recorder
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1) MAGNET:
• Magnets produces the magnetic field, which
determines the frequency of any nucleus.
• Sensitivity and resolution are critically dependent
on quality of magnet.
• It should give homogenous magnetic field, i.e. the
strength of the magnetic field should not change
from point to point.
• The magnet must be capable of producing a very
strong magnetic field with strength atleast 10,000
gauss.
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Types:-
A. Permanent Magnet:
• It is inexpensive and simple to operate, but it requires
extensive shielding and must be thermostated .
• They are operated upto 1.9 T.
• They provide field of good homogeneity.
Disadvantage:-
• Field variation is not possible, as required, because
different nuclei resonate at different magnetic field.
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B) Electro Magnets:
• They require power supply to produce magnetic field
and cooling system to counter the heat generated
from the electric power.
• They are more effective than the permanent magnet
because of possibility of field variation.

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C) Super conducting magnet:
• A super conducting magnet has an electromagnet
made up of superconducting wire.
• Superconducting wire has a resistance approximately
equal to zero by immersing it in liquid helium (at 00 c).
• The length of superconducting wire in the magnet is
typically several miles.

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2) FIELD LOCK :-
• In order to produce a high resolution NMR spectrum
of a sample there is need of homogeneous magnetic
field.
• The field strength might vary due to aging of the
magnet, movement of metal object near the magnet,
and temperature fluctuations.

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3) SHIM COILS:-
• By using these coils Current is adjusted until the
magnetic field has required homogeneity.
• Magnetic field produced by the Shim coils cancels
the small residual inhomogeneities in the magnetic
field.
• These inhomogeneities could be caused by the
magnet design, materials in the probe, variations in
the thickness of the sample tube, Etc.,.

13. 4) PROBE UNIT :-
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a) Sample holder:
• Sample should be held in holder, which should be
chemically inert, durable and transparent to RF radiation.
• Glass tubes of about 8.5cm long and 0.3cm diameter are
employed.
• Glass tube are amberized in order to protect UV sensitive
sample.
• A spinner is provided to spin the tube at several
rotations/min. in order to make the sample experience
homogenous magnetic field.

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B) Radiofrequency oscillator:
• To irradiate the sample with electromagnetic
radiation a highly stable crystal controlled oscillator
coil is imposed at right angle to the applied magnetic
field.
• To achieve maximum interaction of the RF radiation
with the sample the oscillator coil is wound around
the sample cell.

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C) Sweep Generator:
• For a nucleus to resonate, the precession frequency
should become equal to the frequency of the applied
RF radiation.
This can be achieved by,
I. Frequency Sweep method:
• This method is used to resonate the nucleus
• The frequency of the RF radiation is changed so that
it become equal to resonance frequency or
precession frequency.

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ii. 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.

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D) Radiofrequency receiver:
• A few turns wire is wound around the sample
tube tightly.
• This receiver coil is perpendicular to both the
external magnetic field and radio frequency
oscillator.
• When RF radiation is passed through the
magnetized sample, the resonance occurs,
which causes the current voltage across the coil
to drop.

19. 5) DETECTOR :-
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• When radiation is passed through the sample, the
two phenomena namely, absorption and dispersion
may occur.
• The observation of dispersion or absorption will
enable the resonance frequency to be determined.
There are two method to detect the resonance signals.
a)Single coil method (Radiofrequency bridge method)
b)Double coil method (Nuclear induction method)

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a)Single coil method:
(Radiofrequency bridge)
• In this method coil used for surrounding the sample
serves as both transmitter and receiver coil.
• The applied signal is balanced against the received
signal and the resonance signal is recorded as an out
of balance e.m.f which may be amplified and
recorded.

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b) Double coil method (Nuclear induction method):
• In this method there are separate transmitter and
receiver coils.
• These two coils are fixed at right angle to each other
as well on to the direction of external magnetic field.
• This energy transfer (induction) is influenced by
magnetic nuclei in a sample placed between the two
coils, as long as the RF current in the first coil was in
resonance with nuclear transition.

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6) AMPLIFIER & RECORDER:
• The received signal is amplified by the help of
amplifier.
• And it is recorded by using a computer device.

24. REFERENCES :-
• Chatwal GR, Anand SK. Spectroscopy. Himalaya
publishing house; 2006
• YR Sharma. Elementary organic spectroscopy.
• www.google.co.in
• Robert D.B. Introduction to instrumental analysis.
Hyderabad: Pharma book syndicate; 2006
• Hobart H.W, Lynne L.M, Jr, john A.D, Instrumental
method of analysis, CBS publisher & distributors.
• Dr.Ravisankar S. A text book of pharmaceutical
analysis. 3rd ed. Rx Publications; 2001. 24

25. THANK YOU
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