Quiz

• NMR spectroscopy


  Radiation in the radiofrequency region is used to excite atoms, like protons or carbon-13 atoms, so that their spins switch from being aligned with to being aligned against an applied magnetic field. The range of frequencies required for excitation and the complex splitting patterns produced are very characteristic of the chemical structure of the molecule.

  
• Proton spin


  Causes an NMR signal. The nucleus of a hydrogen atom does spin and because hydrogen atoms occur very frequently, they are useful in determining structure.

  
• Nuclei utilized in NMR work

  • 1H (proton)
  • 13C (carbon)

  
• Tetramethylsilane (TMS)


  Chemically unreactive reference standard used in NMR

  
• Sampling for NMR

  1. Solid or liquid sample is first dissolved in solvent free of protons (CCl4, CS2, CDCl3- deuterated chloroform)

  2. Added to NMR sample probe

  3. Followed by standard TMS

  
• Fluorometry


  A type of electromagnetic spectroscopy which analyzes fluorescence from a sample
• Fluorometry


  • Greater sensitivity and specificity
  • Involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain compounds and causes them to emit light of a lower energy
• Fluorometer


  Instrument used for fluorometry
• Applications of fluorometry


  • Analysis of vitamins particularly B1 and B2
  • Determination of fluorescent drugs in low dose formulation
• Limitations of fluorometry


  • Only applies to a limited number of molecules
  • Subject to interference by UV-absorbing species
• Turbidimetry


  Light transmittance as a measure of turbidity
• Nephelometry


  Measurement of the brightness of light reflected by a cloud of finely divided particles suspended in a liquid
• Applications of turbidimetry and nephelometry

  • Antibiotics
  • Calcium pantothenate
  • Vitamin B12
  • Assay of chloride and sulfate
• Analysis of antibiotics using turbidimetry

  1. Antibiotic dilution containing microbiological culture

  2. Increased turbidity (due to microbial growth) indicates less activity of the antibiotic