123 2nd LE

• Atomic Spectra – Absorption of light
• Gaseous atoms can be shown to absorb light by using an absorption spectrum
• CHEMILUMINISCENCE


  MATTER interact with other forms of energy and produce radiation
• Photoluminescence


  matter interact with radiant energy and produce radiant energy
• focuses on the decrease of radiant energy after interacting with matter


  ABSORPTION
• analysis focuses on the radiant energy released after interacting with matter

  EMISSION
• Analyte forms


  Atomic and Molecular + Absorption/Emission + Spectroscopy
• Atomic spectroscopy sample must be in gas phase
• Atomization - nebulize sample then reduce ions to gas atoms
• Atomization process (from solution):

  Nebulize > Desolvate > Volatilize > Dissociate > Ionize
• In atomic absorption, atoms absorb part of the light from the source and the remainder of the light reaches the detector.
• Atomic emission comes from atoms that are in an excited state because of the high thermal energy of the flame.
• General instrumentation AAS


  Source > Sample > Wavelength selector > Detector> Signal Readout
• Atomization: Flames

  1. Premix burner. (b) End view of flame. The slot in the burner head is about 0.5 mm wide. (c) Distribution of droplet sizes produced by a particular nebulizer
• Atomization: Electrothermal Furnace


  Good for dry samples and For samples that are difficult to desolvate, or prepare as solution
• Source in AAS-AES


  Since the transitions between ground state and excited state are very specific per atom, the source of radiation must be exact
• ‘Line’ source for Atomic Spec


  Hollow Cathode Lamp
• Electrodeless Discharge Lamp (EDL

  Main advantage – higher radiant power than HCL Only good for Se, As, Cd, Sb analyses
• Instead of single specific wavelength, ‘band’ spectrum is produced these two sources are

  Doppler effect and collision of atoms
• Interferences in AS


  Spectral Interferences

  Chemical interferences
• Spectral interferences


  line source overlapping wavelenghts

  matrix scattering

  flame condition
• Chemical Interferences


  Ionization of element

  Salt formation
• To minimize spectral interference

  Background correction
• Background correction


  Continuum Source Correction

  Zeeman Background correction
• Continuum Source correction


  Absorbance of the deuterium radiation is then subtracted from that of the analyte beam
• Zeeman Background correction


  Continuous switching of polarizer as polarized light passes through sample results in more improved (higher S/N) signal
• Minimizing chemical interference


  control of sample matrix
• Spectrometer


  info about radiation intensity as a function of wavelength or frequency
• Chromatography - analytical technique that focuses on separation and detection of analyte in a mixture
• Normal phase chromatography


  Non polar mobile phase

  polar stationary phase
• Reverse phase chromatography


  polar mobile phase

  non polar stationary phase
• Volume flow rate


  volume of solvent per time
• Linear flow rate


  distance per time of solvent
• volumetric flow rate 


  = pir^2 *linear flow rate * %occupied by MOBILE PHASE
• tR


  retention time
• Chromatogram info


  signal intensity

  width of peaks

  retention time
• retention time - time it takes for analyte to be eluted from column
• Vr


  retention volume - volume of mobile phase to elute
• tr= tm+ts


  retention time = solvent detection time + solute to be detected after solvent
• retention factor, capacity, partition, ratio


  time to elute a certain peak