Pharm Ana Lec Midterms

• Instrumental Method of Analyses

  • Spectrometry - uses spectrometer and involves the use of light, either absorbed or transmitted, to determine the characteristic of a solution or concentration
  • Chromatography - uses chromatographs and involves separating complex solutions to determine the secondary metabolites or active constituents
  • Electroanalytical Chemistry - uses electrodes dipped in the analyte solution to read the concentration of an ion like cation or anion

  
• Spectrometry


  • Deals with light and its absorption and emission by solutions and other material substances
  • The intensity of transmitted radiant energy is a function of the concentration of chemical species which absorbs the radiant energy

  
• Particle Theory of Light

  Light is made up of moving particles, often called photons or quanta
• Wave Theory of Light

  Light is made up of moving electromagnetic disturbances, referred to as electromagnetic waves
• Equation relating the energy of a photon to the frequency of radiation: E = hv

  
• Equation relating the velocity of light, wavelength and frequency: c = λv

  
• Terminologies


  • Radiant Energy
  • Wavelength
  • Frequency
  • Wave number

  
• Sample Problems


  1. Calculating frequency from wavelength

  2. Calculating wavelength from frequency

  3. Calculating energy from frequency

  4. Calculating energy from wavelength
• Ranges of the λ of the Radiant Energy

  • Ultraviolet (220 - 380 nm)
  • Visible (380 - 780 nm)
  • Near infrared (780 - 3000 nm)
  • Medium infrared (3.0 - 15 μm)
  • Far infrared (15 - 300 μm)

  
• Visible Light Wavelength Ranges

  • 380 - 450 nm (Violet)
  • 450 - 480 nm (Blue)
  • 480 - 490 nm (Green Blue)
  • 490 - 500 nm (Blue Green)
  • 500 - 570 nm (Green)
  • 570 - 590 nm (Yellow)
  • 590 - 620 nm (Orange)
  • 620 - 780 nm (Red)
• Internal Energy Transitions


  • Rotational transition - 3D movement in x, y, or z axis
  • Vibrational transition - changes in bond length
  • Electronic transition - 2D movement
• Chromophore


  A functional group which absorbs radiant energy in the UV or visible region of the spectrum

  
• Colorimetry


  Branch of spectrophotometry where absorption measurement is made in the visible region of the spectrum

  
• Colorimeter and Filter Photometer


  Instruments that use filters instead of prisms/gratings to increase measurement sensitivity, often used for alkali and alkali earth metals
• Bathochromic or Red Shift


  Introduction of NH2 or OH to aromatic system increases the wavelength of absorption
• Hypsochromic or Blue Shift

  Addition of proton to amino group can reduce conjugation, reducing the wavelength of absorption
• Hypochromic Effect


  Decreases the intensity of absorption
• Hyperchromic Effect


  Increases the intensity of absorption
• Absorption Spectrum


  Plot of amount of light absorbed by a sample vs wavelength

  
• Absorbance


  The amount of light absorbed, also known as optical density, absorbancy, or extinction coefficient

  
• Transmission Spectrum


  Plot of the amount of light transmitted by a sample vs wavelength
• Transmittance


  The ratio of the radiant power transmitted by the solution to the radiant power transmitted by the blank
• Frosted


  Can be handled
• Absorption spectrum


  A plot of the amount of light absorbed by a sample vs the wavelength of the light

  
• As you increase the wavelength, there is an increase in absorbance
• The maximum absorbance depends on the sample and varies
• Transmission spectrum


  A plot of the amount of light transmitted by a sample vs the wavelength of the light
• Transmittance


  The amount of light transmitted
• Transmittance is inversely proportional to concentration and absorbance is directly proportional to concentration

  
• Analyzing a sample with high absorbance

  Dilute the sample to get a lower absorbance reading
• Converting absorbance to percent transmittance

  Percent transmittance = 10^(2-absorbance) x 100
• Converting transmittance to absorbance


  Absorbance = -log(transmittance)
• Beer's Law


  The power of a transmitted radiant beam decreases exponentially as the concentration of the solution containing the absorbing chemical species increases arithmetically
• Lambert's or Bouguer's Law


  The power of a transmitted radiant beam decreases exponentially as the thickness of the solution containing the absorbing chemical species increases arithmetically
• Beer-Lambert or Beer-Bouguer's Law


  Relates the power of the incident and the transmitted radiant energy to the thickness and concentration of the solution containing the absorbing chemical species
• Determining molar absorptivity from absorbance, concentration and path length

  Absorbance = molar absorptivity x concentration x path length

  
• Determining concentration from absorbance, molar absorptivity and path length


  Concentration = Absorbance / (molar absorptivity x path length)

  
• Aminacrine


  A highly conjugated acridine ring that produces a complex UV spectrum with absorption maxima at 260, 313, 326, 381, 400 and 422 nm
• The molar absorptivities of aminacrine at 260 and 313 nm are 63,900 and 1130 L/mole cm respectively
• Determining the minimum amount of aminacrine detectable at 260 and 313 nm when A = 0.002


  Minimum amount = 0.002 / (molar absorptivity x 1 cm)