PHARM ANA 2

• Spectrometry


  Science that deals with light and its absorption and emission by solutions and other material substances
• Intensity of transmitted radiant energy

  A function of the concentration of chemical species which absorbs the radiant energy
• Particle theory of light

  Light is consist of moving particles, often called photons or quanta
• Wave theory of light

  Light is consist of moving electromagnetic disturbances, referred to as electromagnetic waves
• Radiant energy


  Energy in UV, visible, and IR regions of the electromagnetic spectrum

  
• Wavelength


  Length of an electromagnetic wave

  
• Frequency


  Number of the moving electromagnetic waves that pass a fixed point in 1 sec
• Wave number


  Reciprocal of wavelength

  
• Calculating frequency from wavelength


  Use formula: c = λv

  
• Calculating energy from frequency

  Use formula: E = hv
• Calculating wavelength from energy

  Use formula: E = hc/λ

  
• Ranges of radiant energy wavelengths

  • Ultraviolet: 220 - 380 nm
  • Visible: 380 - 780 nm
  • Near Infrared: 780 - 3000 nm
  • Medium Infrared: 3.0 - 15 μm
  • Far Infrared: 15 - 300 μm

  
• Colours absorbed and transmitted at different visible wavelengths

  • 380 - 450 nm: Violet absorbed, Yellow-green transmitted
  • 450 - 480 nm: Blue absorbed, Yellow transmitted
  • 480 - 490 nm: Green-blue absorbed, Orange transmitted
  • 490 - 500 nm: Blue-green absorbed, Red transmitted
  • 500 - 570 nm: Green absorbed, Purple to red-violet transmitted
  • 570 - 590 nm: Yellow absorbed, Blue transmitted
  • 590 - 620 nm: Orange absorbed, Green-blue transmitted
  • 620 - 780 nm: Red absorbed, Blue-green transmitted

  
• Types of internal energy transitions


  • Rotational transition
  • Vibrational transition
  • Electronic transition

  
• Chromophore


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


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

  
• Colorimeter and filter photometer


  Instruments which use a filter instead of a prism or diffraction grating to increase the sensitivity of the measurement
• Bathochromic or red shift


  Introduction of NH2 or OH to aromatic system, increases the wavelength of absorption
• Hypsochromic shift or blue shift

  Addition of proton to amino group can reduce conjugation, reduction of wavelength of absorption
• Hypochromic effect


  Decreases the intensity of absorption
• Hyperchromic effect


  Increases the intensity of absorption
• Absorption spectrum


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

  
• Absorbance


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

  
• Transmission spectrum


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

  
• Transmittance


  The ratio of the radiant power transmitted by the solution to the radiant power transmitted by the blank
• Converting absorbance to transmittance

  Use formula: T = 10^(-A)
• Converting transmittance to absorbance


  Use formula: A = -log(T)
• 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
• Calculating molar absorptivity from absorbance, concentration and path length


  Use formula: A = εbc
• Calculating concentration from absorbance, molar absorptivity and path length


  Use formula: A = εbc

  
• Calculating minimum detectable amount from absorbance, molar absorptivity and path length


  Use formula: A = εbc
• Beer's plot


  A plot of absorbance values against a series of known solute concentrations, used to determine unknown solute concentration
• Preparing sample for analysis

  Weigh accurately, transfer to beaker, add 1N HCl, heat and stir, filter to remove insoluble excipients, collect filtrate in volumetric flask, dilute to volume
• Absorptivity


  Absorbance of 0.7 in a 1 cm path length
• Beer's Plot is a plot of absorbance values against a series of known solute concentrations that should yield a straight line
• From a Beer's Plot, the unknown solute concentration is determined by measuring the absorbance value of the solution and finding the concentration value which corresponds to the measured absorbance value
• A spectrophotometer is an instrument used to measure the absorbance or transmittance of a solution as a function of wavelength
• Ultraviolet and Visible Spectroscopy


  Radiation in the wavelength range 200 – 700 nm is passed through a solution of a compound, causing the electrons in the bonds within the molecule to become excited and occupy a higher quantum state, absorbing some of the energy passing through the solution