Nuclear magnetic resonance ( NMR)

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NMR spectroscopy and its application in food industry.

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Nuclear magnetic resonance ( NMR)

  1. 1.  NUCLEAR MAGNETIC RESONANCE SECTROSCOPY
  2. 2. iNTRODUCTION  Powerful analytical technique used to characterize organic molecules by identifying carbon-hydrogen frameworks within molecules.  2 Types :  The source of energy in NMR is radio waves which have long wavelengths, and thus low energy and frequency.  This waves can change the nuclear spins of some elements, including 1H and 13C.  Frequency in the range of 300Mhz-500Mhz. 13C -NMR1H -NMR
  3. 3.  Energy state Less in no. Anti parallel to applied field. Beta More in no. Parallel to applied field. Alpha (Diff < 0.1cal)
  4. 4.  The frequency needed for resonance and the applied magnetic field strength are proportionally related:  These spectrometers use very powerful magnets to create a small but measurable energy difference between two possible spin states
  5. 5. An NMR machine consists of:  (1) A powerful, supercooled magnet (stable, with sensitive control, producing a precise magnetic field).  (2) A radio-frequency transmitter (emitting a very precise frequency).  (3) A detector to measure the absorption of radiofrequency by the sample.  (4) A recorder (to plot the output).
  6. 6. diagram:
  7. 7.  An NMR spectrum is a plot of the intensity of a peak against its chemical shift, measured in parts per million (ppm).
  8. 8. 1H NMR—The Spectrum  NMR absorptions generally appear as sharp peaks.  Increasing chemical shift is plotted from left to right.  Most protons absorb between 0-10 ppm.  The terms “upfield” and “downfield” describe the relative location of peaks. Upfield means to the right. Downfield means to the left.  NMR absorptions are measured relative to the position of a reference peak at 0 ppm on the d scale due to tetramethylsilane (TMS). TMS is a volatile inert compound that gives a single peak upfield from typical NMR absorptions
  9. 9. 1H NMR—Number of Signals  The number of NMR signals equals the number of different types of protons in a compound.  Protons in different environments give different NMR signals.  Equivalent protons give the same NMR signal.
  10. 10. 1H NMR—Position of Signals  Since the electron experiences a lower magnetic field strength, it needs a lower frequency to achieve resonance. Lower frequency is to the right in an NMR spectrum, toward a lower chemical shift, so SHIELDING shifts the absorption upfield.
  11. 11. Calculating SHIFT VALUES: (H ydrogen under consideration)C C H H H H H Cl   Base Chem ical Shift = 0.87 ppm no substituents = 0.00 one  -Cl (CH 3) = 0.63 TO TAL = 1.50 ppm (H ydrogen under consideration)C C H H H H H Cl  Base Chem ical Shift = 1.20 ppm one  -Cl (CH 2) = 2.30 no substituents = 0.00 TO TAL = 3.50 ppm
  12. 12. energetic status of cells to monitor the fermentation of yoghurts (using phosphorus 31 LR NMR) Analysis of sample quality and in process control cooking of various types of rice (proton NMR) examination of cell cultures in the mashing of beer (using proton NMR) Applications
  13. 13. Carbohydrate NMR Spectroscopy  structure of monosaccharides and oligosaccharides.  sugar conformations.  500 MHz or greater.  3 – 6 ppm. (13C NMR chemical shifts of carbohydrate ring carbons are 60 – 110 ppm).

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