Nuclear Magnetic ResonanceANIMATED ILLUSTRATIONS

MS Powerpoint Presentation Files

Uses Animation Schemes as available in MS XP or MS

2003 versions

A class room educational material

File-5 NMR Spectrometer: Instrumentation

http://ugc-inno-nehu.com/links_from_web.html

cosine Sine arbitrary phae sinuous

Z-direction

Z-d

irec

tion

100 MHz Electro-magnet/Permanent magnet Systems

Supercon magnet systems above 100MHz up to 900MHz as known currently

Magnet Current source

Superconducting current carrying coils

Pulse widths could be

10-2 μs

CW RF Oscillator mw power

RF Crystal Detector

Display/RecordPulsed RF Transmitter

Probe with sample coil and 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 Mode of detectio

n

Pulsed Mode of

Detection

Flowing Current and Induced Magnetic Fields in a Solenoid

Electrons (Blue Circles) Move and 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.)

-1.50

-1.00

-0.50

0.00

0.50

1.00

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

Free Induction Digitized

FID analog signal

FID digitized points

Received Analog Signal

Analog to Digital

Converter

A D C

Digitized Signal

FID

FT Real

FT Imag.

Integration

All the signal shapes have been calculated in MS EXCELIn 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

ADC

CW RF Source Gate

Pulse Programmer

DC Pulse

Power Amplifier

Rectangular RF Pulse

Sample coil in the Probe with sample

Low noise RF Preamplifier

FID

High Gain Signal Amplifier

Phase Sensitive DetectorReference Signal

computer [FFT]

Spectrum to display monitor/Plotter

High Power RF Pulses to Probe

HR NMR in Liquids 100W NMR of Solids 3KW PP Matched 50 Ω

Time Domain signal

TransmitterReceiver

CW Mode

Sample tube with sample

RF Bridge (Hybrid Junction)

RF Source (sweep generator)

Scope

50Ω

RF Signal receiver- detector

Basic Probe unit is a Resonance Circuit with tunable split capacitors configuration for matching.

CW Mode

High-Power pulse transmitter

Receiver off time

Low noise pre-amplifier /high gain receiver/PSD/Digital computer/Plotter

Pulsed RF mode

Transmitter ON time

Probe & sample

Crossed Diodes

ReceiverReceiver OFF 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

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: Shimmimng the magnetic field using gradient correction coils and sample spinning are the provisions in the spectrometer system for improving the homogeneity

Signal level

Noise Level

HR PMR ch3ch2oh

0

1

2

3

4

5

23487398123148173198223248273298323348

frequency from TMS

Inte

nsi

ty/A

mp

litu

de

HR PMR ch3ch2oh

Moderate Resolution

HR PMR Spectrum

CH3

CH2OH

δ= 1.13 ppm

TMS δ= 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 ppm3.61 ppm

1.13 ppm0

OH-CH2-CH3

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 same nmr frequency for the sample

NMR frequency will vary linearly along the length.

In the Pulsed Field Gradient PFG and Magnetic Resonance Imaging

MRI techniques calculated field gradient are externally superposed.

The inherent unwanted and incidental inhomogeneities are reduced by Shimming and sample spinning