ANACHEM

• Spectrochemical methods


  Instrumental methods of analysis that involve the absorption or emission of light

  
• Spectroscopy/spectrometry


  The science that deals with light and its absorption and emission by solutions and other material substances
• Spectrometer


  The broad term for the instrument used
• Spectrophotometer


  A more specific term when a light sensor known as a phototube is used

  
• Spectrochemical analysis


  The degree to which light is absorbed, or the intensity of light that is emitted, is related to the amount of an analyte present in the sample tested

  
• Light


  • Has a dual nature - it can be described as consisting of moving particles (photons) or moving electromagnetic disturbances (electromagnetic waves)
• Wavelength


  The length of an electromagnetic wave, symbol λ

  
• Frequency


  The number of the moving electromagnetic waves that pass a fixed point in 1 sec, symbol ν

  
• Frequency and energy


  Are directly proportional
• Wavelength


  Is inversely proportional to frequency and energy

  
• Regions of the electromagnetic spectrum


  • Visible
  • Ultraviolet
  • Infrared
  • X-ray
  • Radio and television waves

  
• Visible region


  Wavelengths that vary from approximately 350 nm to approximately 750 nm

  
• Radio and television waves


  Very low energy waves that do no harm

  
• Microwaves


  Wavelengths on the order of a centimeter, can be dangerous due to internal heat generation
• Infrared region


  Wavelengths are extremely short, higher energy but cause no harm
• Ultraviolet region


  Wavelengths are shorter and have higher energy, can cause harm like sunburn
• 1. rays


  Extremely short wavelengths of extremely high energy, penetrate skin and tissue and cause harm
• Gamma rays


  Wavelengths on the order of atomic diameters, cause extreme damage to the human body due to extremely high energy
• Color of objects


  Some visible light wavelengths are absorbed, the remaining wavelengths are reflected or transmitted and give the object its color

  
• UV-VIS spectrophotometry


  Technique for measuring absorption of molecules in the ultraviolet and visible regions

  
• IR spectrometry


  Technique for measuring absorption of molecules in the infrared region
• Atomic spectroscopy


  Technique for measuring absorption of atoms
• Absorption spectrum


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

  
• Transmission spectrum


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

  
• Absorption and transmission spectra are unique for each compound or ion, and thus are useful for identification and detecting impurities
• Transmittance (T)


  The fraction of light transmitted, equal to I/I0

  
• Absorbance (A)


  A parameter that increases linearly with concentration, calculated as A = 2 - log %T
• Beer's law


  States that the concentration of the unknown substance is directly proportional to the absorbed light (absorbance) and inversely proportional to the amount of transmitted light (% transmittance)
• Absorptivity (a)


  The inherent ability of a chemical species to absorb light, constant at a given wavelength, pathlength, and concentration

  
• Wavelength of maximum absorbance

  The wavelength at which the absorptivity is a maximum, providing the greatest analytical sensitivity

  
• UV-VIS molecular spectrometry


  Utilizes light in the ultraviolet and visible regions to analyze molecular compounds and complex ions

  
• Light sources


  • Tungsten filament lamp for visible light, deuterium lamp for ultraviolet, xenon arc lamp for both UV and visible
• Deuterium lamp


  Contains deuterium at low pressure, emits continuous UV light from 185 nm to 375 nm
• Xenon arc lamp


  Contains xenon at high pressure, forms light via an electric arc
• Spectrophotometer


  Instrument that uses a light source, monochromator, sample compartment, and detector to measure the absorbance of a sample

  
• Light sources used in spectrophotometers

  • Deuterium lamp
  • Tungsten filament lamp
  • Xenon arc lamp
• Deuterium lamp


  • Emits UV light from 185 nm to 375 nm
  • Light is produced by electricity applied to electrodes in the lamp
• Tungsten filament lamp


  • Emits light over the entire visible region and into the near infrared region
• Xenon arc lamp


  • Emits a continuous ultraviolet and visible light
  • Lamp contains xenon at high pressure and light is formed via a discharge across electrodes
  • Can produce regular pulses of intense light
• Wavelength selection


  1. Light from source passes through entrance slit

  2. Light is dispersed by dispersing element (prism or diffraction grating)

  3. Narrow wavelength band is selected by exit slit