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Nuclear Magnetic Resonance

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Presentation on theme: "Nuclear Magnetic Resonance"— Presentation transcript:

1 Nuclear Magnetic Resonance
ANIMATED 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

2 Pulse widths could be 10-2 μs
100 MHz Electro-magnet/Permanent magnet Systems Z-direction Supercon magnet systems above 100MHz up to 900MHz as known currently Z-direction Magnet Current source Superconducting current carrying coils

3 Pulsed Mode of Detection
CW RF Oscillator mw power CW Mode of detection Pulsed Mode of Detection RF Crystal Detector Display/Record Pulsed RF Transmitter Signal receiving and detection High gain RF receiver/detector Probe with sample coil and sample in Magnetic Field Time domain signal to computer for FFT Signal generation Display monitor/Plotter

4 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.)

5 PEAK to PEAK PULSE Amplitude

6 Analog to Digital Converter
Free Induction Digitized Analog to Digital Converter A D C Received Analog Signal Digitized Signal FID analog signal FID digitized points

7 Frequency Domain Spectra after FT
All the signal shapes have been calculated in MS EXCEL In practice FFT program calculates Frequency domain spectra from the time domain signal Integration FID FT Imag. Time Domain Signal FT Real Pulsed detection mode Frequency Domain Spectra after FT Similar to the CW mode Spectra

8 Phase Sensitive Detector
HR NMR in Liquids 100W NMR of Solids 3KW PP Matched 50 Ω Sample coil in the Probe with sample Power Amplifier High Power RF Pulses to Probe Spectrum to display monitor/Plotter Rectangular RF Pulse FID CW RF Source Gate Low noise RF Preamplifier DC Pulse computer [FFT] High Gain Signal Amplifier Pulse Programmer Time Domain signal Phase Sensitive Detector ADC Reference Signal Transmitter Receiver

9 Sample tube with sample
Basic Probe unit is a Resonance Circuit with tunable split capacitors configuration for matching. Sample tube with sample Low noise pre-amplifier /high gain receiver/PSD/Digital computer/Plotter High-Power pulse transmitter RF Bridge (Hybrid Junction) RF Source (sweep generator) RF Signal receiver- detector Scope Receiver off time Pulsed RF mode CW Mode CW Mode 50Ω

10 DATA acquisition starts at this time
5 2 3 4 1 Probe & sample Crossed Diodes Transmitter ON time Receiver Receiver Silent or dead time Receiver OFF time DATA acquisition starts at this time 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

11 Signal level Noise Level 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 Long T2 Short T2


13 OH-CH2-CH3 Acidic medium: spin coupling for OH protons do not show up CH3 3.61 ppm 5.24 ppm 1.13 ppm CH2 OH TMS δ= 0 ppm Moderate Resolution δ= 1.13 ppm HR PMR Spectrum 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.

14 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 NMR frequency will vary linearly along the length. 3 lines inside 6 lines inside Along the length same nmr frequency for the sample Linear Field Gradient along z-axis. Equal number of lines pass through fixed area of cross section along the length

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