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Nuclear Magnetic Resonance

ANIMATED ILLUSTRATIONS

MS Powerpoint Presentation Files

Uses Animation Schemesas available in MS XP or MS 2003 versions

A class room educational material

File-5 NMR Spectrometer: Instrumentation

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cosine Sine arbitrary phae sinuous

Z-direction

Z-di

rection

100 MHzElectro-magnet/Permanent magnet

Systems

Supercon

magnet systems

above 100MHzup to 900MHz as

known currently

Magnet

Currentsource

Superconduc

ting current

carrying coils

Pulse widths

could be

10-2 s


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CW RF Oscillatormw power

RFCrystal

Detector

Display/RecordPulsed RF Transmitter

Probe with

sample coiland sample

in Magnetic

Field

High gain RF

receiver/detector

Time domain signal

to computer for FFT

Display monitor/Plotter

Signal

generation

Signal

receiving

and

detection

CW Modeof

detection

Pulsed

Mode of

Detection


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Flowing Current and Induced

Magnetic Fields in a Solenoid

Electrons (Blue

Circles) Moveand the

Conventional

Current Flows

in the Opposite

direction.

The MOTION of the (red)isolated (?) northpoles indicate the induced field

distributions and in reality there are no lines existing for the LINES of FORCES (as

drawn in the previous slide. It is a virtual line and LOCUS of the point North pole.)


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-1.50

-1.00

-0.50

0.00

0.501.00

1.50

0.0 5.0 10.0 15.0 20.0 25.0

cosine Exponenetial product(cos*exp)=fid

PULSE WIDTHPEAK to PEAK PULSE Amplitude


6/14

Free

Induction

Digitized

FID analog signal

FID digitized points

Received

Analog

Signal

Analog to

Digital

Converter

A D C

Digitized

Signal


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FID

FT Real

FT Imag.

Integration

All the signal shapes have been calculated in MS EXCEL

In practice FFT program calculates Frequency domain spectra from the time domain signal

Time Domain Signal

Frequency Domain Spectra after FT

Similar to the CW mode Spectra

Pulsed

detection

mode


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ADC

CW RF

Source Gate

Pulse

Programmer

DC Pulse

Power

Amplifier

Rectangular RF Pulse

Sample

coil in the

Probe

withsample

Low noise RFPreamplifier

FID

High Gain Signal

Amplifier

Phase Sensitive

DetectorReference Signal

computer

[FFT]

Spectrum to

display

monitor/Plotter

High Power

RF Pulses toProbe

HR NMR in

Liquids 100W

NMR of Solids

3KW PP

Matched 50

TimeDomain

signal

Transmitter

Receiver


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CW Mode

Sample

tube with

sample

RF Bridge

(HybridJunction)

RF Source(sweep

generator)

Scope

50

RF Signal

receiver-

detector

Basic Probe unit is a

Resonance Circuit

with tunable splitcapacitors

configuration for

matching.

CW Mode

High-Power pulse

transmitterReceiver

off time

Low noise

pre-amplifier

/high gain

receiver/PSD/

Digital

computer/Plo

tterPulsed RF mode


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Transmitter ON

time

Probe &

sampleCrossed Diodes

ReceiverReceiverOFF time

Receiver

Silent or dead

time

DATA

acquisition

starts at this

time

12345

After the RF pulse, the FID is the

impulse response from the sample

spin system. The pulsing and FID can

be repeated and added to acquire the

averaged signal for better signal to

noise ratio


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exp1.9 exp2.8 exp5.8 exp8 exp12

exp1.9 exp12

Long T2

Short T2

Achieving a Sharp signal

depends on the homogeneity

of the magnetic filed:Shimmimngthe magnetic

field using gradient

correction coils and sample

spinning are the provisions in

the spectrometer system for

improving the homogeneity

Signal

level

Noise

Level


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13/14

HR PMR ch3ch2oh

0

1

2

3

4

5

23487398123148173198223248273298323348

frequency from TMS

Intensity/Amplitude

HR PMR ch3ch2oh

Moderate Resolution

HR PMR Spectrum

CH3

CH2OH

= 1.13 ppm

TMS= 0 ppm

Acidic medium: spin coupling

for OH protons do not show up

This calculated and simulated [60 MHz] spectrum has the chemical shift

and frequency values as obtained from a real NMR spectrum of alcohol.

The above figure plotted using MS Excel application and line drawing

from MS WORD drawing tools.High Resolution spectrum as shown

above would be possible with good homogeneity of the magnetic field.

5.24 ppm

3.61 ppm1.13 ppm

0

OH-CH2-CH3


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Equal number of lines pass through fixed area

of cross section along the length

3 lines

inside

6 lines

inside

Linear Field Gradient

along z-axis.

Along the length samenmr frequency for the

sample

NMR

frequency

will vary

linearlyalong the

length.

In the Pulsed Field GradientPFGand Magnetic Resonance Imaging

MRItechniques calculated fieldgradient are externally superposed.The inherentunwanted and

incidental

inhomogeneities

are reduced by

Shimming and

sample spinning

0 5 instrmtn nmr spctromtr

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