NMR PRINCIPLE INSTRUMENTATION

1. PRESENTATION ON
NUCLEAR MAGNETIC RESONANCE
SPECTROSCOPY
PRESENTED BY
HIMAJA.D
H.T.NO.636217885001
M. pharmacy 1stYear
Under The Guidance Of
Dr. S.Y MANJUNATH Ph.D
Department Of Pharmaceutical Analysis
SRIKRUPA INSTITUTE OF PHARMACEUTICAL SCIENCES
{Approved by AICTE, PCI }
{Affiliated to OSMANIA University}

2. INTRODUCTION
 NMR is a branch of spectroscopy in which radio frequency waves
{60-800MHz}induce transitions between magnetic energy levels
of nuclei of a molecule.
 Sample is subjected with two magnetic field, one is stationary and
another is varying at same radio frequency.
 Combination of these two field energy is absorbed by sample and
signal is obtained .
 When electromagnetic field provided to the nucleus of the sample.
 Nucleus start spin around the nuclear axis and generate another
magnetic field. Combination of these two field, the energy is
absorbed by nucleus, this technique is called as NMR spectroscopy.
 Nuclear magnetic resonance spectroscopy(NMR) is a powerful
analytical technique used to characterize organic molecules by
identifying carbon-hydrogen frameworks within molecules.

3. TYPES OF NMR
Two common types of NMR spectroscopy are used to characterize
organic structure:
1} 1H NMR:- Used to determine the type and number of H atoms in a
molecule. An NMR spectrum is a plot of the intensity of a peak
against its chemical shift, measured in parts per million(ppm)
2} 13C NMR:- Used to determine the type of carbon atoms in the
molecule.

4. PRINICIPLE
 The sample is dissolved in a solvent, usually CDCl3(deutero-
chloroform), and placed in a magnetic field.
 A radiofrequency generator then irradiates the sample with a
short pulse of radiation, causing resonance.
 When the nuclei fall back to their lower energy state, the detector
measures the energy released and a spectrum is recorded
 Protons in different environments absorb at slightly different
frequencies, so 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 a narrow range of frequencies is applied to
achieve the resonance of all protons.

5.  Only nuclei that contain odd mass numbers (such as 1H, 13C, 19F
and 31P) or odd atomic numbers (such as 2H and 14N) give rise to
NMR signals.
900 MHz NMR Instrument with a 21.1 T
Permanent Magnet.

6. NMR INSTRUMENTATION
1. Sample Holder
2. Permanent Magnet
3. Probe
4. Sweep Generator
5. Radio Frequency
Transmitter
6. Radio Frequency
Receiver
7. Read Out
Systems

7. 1.Sample Holder:-
Sample should be held in a holder which should be
chemically inert, durable and transparent to radiation.
Glass tube with 8.5cm long,0.3 cm in diameter. The sample
holder in NMR is normally tube-shaped and is therefore
called the sample tube.
Glass or Pyrex tubes are commonly used.

8. 2. Permanent Magnet:-
The important feature of the magnet it should gives
homogeneous magnetic field i.e., the strength & direction of
magnetic field should not change from point to point. The
strength of the field should be very high i.e. atleast 20000
gauss(G) electro magnets are more stable than permanent
magnets.
Range from 60 MHz (1.4 T) to 700 MHz (16.4 T) and
higher.
1HNMR Operates at 60-100 MHz
13CNMR Operates at 200-600MHz
There are two parts of magnet-
a) Superconducting magnet
b) Shim Coils

9. a)Superconducting magnet-
• It is made up of
superconducting Nb/Sn or
Sb/Ti wire.
• The magnet is submerged liquid
helium, for providing the
sufficient cooling.
• The magnet and the liquid
helium reservoir are encased
in a liquid nitrogen reservoir to
decrease the evaporative loss of
more expensive liquid helium.
• The sample probe is put in the
bore.

10. b)Shim Coils-
• Shim coils are used for
making magnetic field
homogeneous,
provided by the
magnets.
• Through these coils current
is adjusted until the
magnetic field has the
required homogeneity.

11. 3.Probe:-
 In which the sample holder is
placed.
 Contains an Air turbine to spin the
sample holder, while the spectrum
is collect.
 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
frequency probe is needed (mean:
a separate probe is required for
each nucleus like1H, 13C, 19F).

12. 4.Sweep Generator:-
To produce a amount of magnetic field pass through the sample. 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.
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.
5.Radio Frequency Transmitter:-
The RF radiation is generated by RF crystal oscillator.
The output of the oscillator is amplified, mixed, and filtered to produce
monochromatic RF radiation and delivered to the sample.
A radio transmitter coil that produces short powerful pulse of radio waves.

13. 6.Radio Frequency Receiver:-
A radio receiver coil that detects radio frequencies emitted as nuclei relax to
lower energy level.
The NMR signal emanating from the probe is detected by a digitizer receiver
at regular time intervals.
These signals in the time domain must be converted to a frequency domain
spectrum by application of a “Fourier transformation” or other
mathematical transformation
7.Readout System:-
A computer that analyses and record the data.

14. SOLVENTS USED IN NMR
 Frequently the sample cannot be obtained in the pure state (or) it may be
in the solid (or) gas phase.
 Most NMR spectra are recorded for compounds dissolved in a solvent.
Therefore, signals will be observed for the solvent and this must be
accounted for in solving spectral problems.
 It may be necessary to dissolve it or extract it for some other medium in
this case a solvent must be used. Several requirements must retain by a
good solvent, including then it
i) It can be Chemically inert towards the sample,
ii) It should not interfer with NMR absorption spectrum,
iii) The using solvents should not contain HYDROGEN in the molecule.
 A substance free of proton should be used as a solvent, i.e., which does not
give absorption of its own in NMR spectrum.
 Moreover, the solvent should be capable of dissolving at least 10% of the
substance under investigation.
 The best solvents for proton NMR contain No protons.

15.  To avoid spectra dominated by the solvent signal, most 1H NMR spectra are
recorded in a deuterated solvent{deuterium nucleus does not respond, in the
same region as the hydrogen nucleus}. However, deuteration is not "100%", so
signals for the residual protons are observed. In chloroform solvent (CDCl3),
this corresponds to CHCl3, so a singlet signal is observed at 7.26 ppm.
 The following solvents are normally used in which hydrogen replaced by
deuterium.
CCL4 - Carbon Tetrachloride
CS2 - Carbon disulfide
CDCL3 - Deuteriochloroform
CDCl3 is a common solvent used for NMR analysis. It is used because most
compounds will dissolve in it, it is volatile and therefore easy to get rid of,
and it is Non-reactive and will not exchange its deuterium with protons in
the molecule being studied.
C6D6 - Hexa deuteriobenzene
D2O - Deuterium oxide
(CCL3) 2CO - Hexa chloroacetone

16. APPLICATIONS
 Nuclear Magnetic Resonance (NMR) Spectroscopy is a non-
destructive analytical technique that is used to probe the nature
and characteristics of molecular structure. A simple NMR
experiment produces information in the form of a spectrum,
which is able to provide details about. The types of atoms present
in the sample.
 It has applications in a wide range of disciplines, and development
of new applied methods for NMR is an active area of research.
Methods in NMR spectroscopy have particular relevance to the
following disciplines:
◦ Structure elucidation
◦ Chemical composition determination
◦ Formulations investigation
◦ Mixture analysis
◦ Sample purity determination

17.  Purity determination (w/w NMR)
NMR is primarily used for structural determination, however it can
also be used for purity determination, providing that the Structure
and Molecular weight of the compound is known. This technique
requires the use of an Internal standard of a known purity.
Where:
wstd: Weight of Internal standard
wspl: Weight of Sample
n[H]std: The integrated area of the peak selected for comparison in the standard,
corrected for the number of protons in that Functional group
n[H]spl: The integrated area of the peak selected for comparison in the sample,
corrected for the number of protons in that Functional group
MWstd: Molecular weight of Standard
MWspl: Molecular weight of Sample
P: purity of Internal Standard

18. • IN MEDICINES
The application of nuclear magnetic resonance best known to the
general public is Magnetic Resonance Imaging for medical diagnosis
and Magnetic Resonance Microscopy in research settings.
However, it is also widely used in chemical studies, notably
in NMR spectroscopy such as proton NMR,
carbon-13 NMR,
Deuterium NMR and
Phosphorus-31 NMR.
Biochemical information can also be obtained from living tissue.
E.g. Human brain tumors
with the technique known as In Vivo Magnetic Resonance Spectroscopy
or chemical shift NMR Microscopy

19.  Chemistry
By studying the peaks of nuclear magnetic resonance
spectra, chemists can determine the structure of many
compounds.

20. NMR SPECTRUM OF TOLUENE
Toluene is having 8 protons, 5 of which are aromatic and remaining 3 of
methyl group.
The signal for 3 protons of methyl group which is joined to an aromatic
ring appears as a singlet at 2.34.
Theoretically the 5 aromatic protons are non-equivalent & of 3 different
kinds(i.e., 2 ortho , 2 meta & 1 para protons with respect to methyl
group) Hence these protons do not couple with each other & give rise to
only 1 signal in the form of a singlet at 8.18.

21. REERENCES
 Instrumental Methods of Chemical Analysis
By Gurdeep R. Chatwal,
Sham K. Anand.
 Elementary Organic Spectroscopy
By Y.R. Sharma.
 Principles of Instrumental Analysis
By Doglas A Skoog.
 Pharmaceutical Drug Analysis
By Ashutosh kar.