instrumentation of nmr

1. INSTRUMENTATION OF NMR:
PRESENTED BY:MR.SANJAY KUMAR SAH
M.PHARM1ST YEAR
DEPARMENT OF PHARMACEUTICS
GUIDED BY:PROF. T SHRINIVAS
DEPARTMENT OF PHARMACEUTICAL ANALYSIS

2. CONTENT
 TYPES OF NMR INSTRUMENT/SPECTROPHOTOMETERS
 INSTRUMENTATION
 COMPONENTS OF NMR ISTRUMENTATION
 TECHNIQUES AND PRINCIPLE
 REFERENCE

3. introduction
 NMR spectroscopy may be of single coil spectrometers =
in which absorption is measured
 And double coil instruments=in which resonant radiation
is measured
 Spectrometers may further divided into low resolution
instruments and high resolution instruments.
 The high resolution instruments are capable of resolving
the fine structure that is associated
With the absorption peak for given nucleus.
 A high resolution spectrometer can evidence two distinct
types of structure in
NMR absorption due to proton resonance ,known respectively
as the chemical
Shift and spin spin coupling.

4. instrumentation

5. Components of
NMR
instrumentation
Magnets Magnetic coils Probe unit
Radiofrequency
generator
Sweep
generator
Radiofrequency
receiver or
detector
Recorder

6. 1.MAGNETS
 Magnet is used to supply the
principle part of the field, which
determines the frequency of any
nucleus.
 The stronger the magnetic field, the
better the line separation of
chemically shifted nuclei on the
frequency scale.

7. Features
It should give
homogeneous magnetic
field ie; the strength and
direction of the magnetic
field should be constant
over longer periods.
The strength of the field
should be very high at
least 20,000 gauss.
If the magnetic field is
not homogenous the
nuclei in the different
part of sample process
with different
frequencies there by
producing broad signals.
Generally permanent and
conventional
electromagnets are used
in spectrometers
operating up to 100 MHz
to 230 MHz

8. 2.Magnetic coils/the
magnetic field sweep
 It is not easy or convenient to vary
the magnetic field of large stable
magnets, however this problem
can be overcome by superimposing
a small variable magnetic field on
the main field. Using a pair of
Helmholtz coils on the pole faces
of the permanent magnet.
 These coils induce a magnetic
field that can be varied by varying
the current flowing through them.

9. 3.The probe unit
 It is a sensing element of the
spectrophotometer system. It is
inserted between the pole faces of
the magnet in X-Y plane of the
magnet air gap an adjustable probe
holder.
 So the sample in NMR experiment
experiences the combined effect of
two magnetic fields.
 The probe contains a sample
holder, sweep source and detector
coils, with the reference cell. The
detector and receiver coils are
orientated at 90 to each other. The
sample probe rotates the sample
tube at a 30-40 revolutions on the
longitudinal axis.
 These rotation minimizes the
effects of inhomogeneities in field
and as a consequence sharper lines
and better resolution are obtained.

10. 4.The sample holder
NMR sample cell
consists of a
7.5cm to 0.3 in
diameter.
The sample
holder should be
chemically inert,
durable and
transparent to
radio wave.
Generally the
glass tubes are
sturdy
,practicable and
cheap.
The sample must
be in the liquid
or solution state
for high
resolution
spectra.

11. 5.Radio frequency generator
 Using an RF oscillator required to induce transition in the nuclei of the sample from the ground state
to excited states creates the radio frequency radiation.
 To achieve the maximum interaction of the RF radiation with the sample, the coil of oscillator is
wound around the sample container.
 The RF coil is installed perpendicular (90) to the applied magnetic field and transmits radio waves of
fixed frequency such as 60,100,200 or 300 MHz to a small coil that energies the sample in the probe.
This is done so that the applied field should not change the effective magnetic field in the process of
irradiation.
 Oscillators used in NMR spectrophotometers are,
1. Robinsons valve version oscillator
2. Robinsons field effect transistor version oscillator.
3. W.D.Knights oscillator.
4. Tunable low temp oscillator
5. New sensitive marginal oscillator
6. P.K.W oscillator etc.,

12. 6.Radio frequency receiver
 A few turns of wire is wound around the sample tube
lightly.
 This receiver coil is perpendicular to both the external
magnetic and radiofrequency transmitter coil.
 When RF radiation is passed through the magnetised
sample resonance occurs which cause the current
voltage across the coil to drop.
 Hence two phenomena ,namely absorption and
dispersion may occur . The lines shapes are the
interpretation of absorption spectrum and it is easier as
compared to dispersion spectrum.

14. 7.The signal
detector and
recording
system
 The detector should be capable of separating
absorption from dispersion signal and from that of the
Rf oscillator.
 There are two main methods of detection.
 1.use a radio frequency bridge.
 2. employs a separate receiver coil.
 now these coils used
to direct the radio frequency signal produced by the
resonating nuclei. The electrical signal generated into
the coil must be amplified before it can be recorded.

15. Techniques and
principle
 A radio frequency oscillator
which is adjusted to generate a
certain preset or definite
frequency v which passes
through a coil located between
the magnetic poles surrounding
the sample , is a receiver coil.
The receiver coil is used to pick
up the broadcast signal. These
signals are carried to a receiver
and amplifier and then to a
cathode ray oscillograph
recorder.

16. Cont..

17. Reference
1. Willard H.H, Meritt Jr.L.L, Dean J.A, Settle
Jr.F.A, Instrumental methods of analysis, 7th
edition.427-438.
2. Donald.L.P, Lampman G.M, George S.K,
Introduction to spectroscopy, 3rd edition.113-
116.
3. Skoog D.A, Holler F.J, Nieman T.A, Principles of
instrumental analysis, 5th edition.470-473.
4. Silverstein R.M, Webmaster F.A, Spectrometric
identification of organic compounds, 6th
edition.148-150

18. Thank
you