anachem II spectroscopy instruments

• Optical methods

  • spectroscopic methods based upon

  ultraviolet, visible, and infrared

  radiation
• Types of Optical Spectroscopy

  • UV-vis absorption spectroscopy (UV-Vis)

  • FT-IR absorption/transmission spectroscopy

  (FTIR)

  • Atomic absorption spectroscopy (AAS)

  • Atomic fluorescence spectroscopy (AFS)

  • X-ray fluorescence spectroscopy (XFS)
• fill

  A) source

  B) wavelength selector

  C) detector

  D) source

  E) wavelenght sletor

  F) signal processor and readout

  G) source

  H) sample

  
• Optical Materials

  • The cells, windows, and wavelength-

  dispersing elements in a

  spectrophotometer or photometer

  must be transparent in the

  wavelength region being employed

  for analyses.
• Light sources

  Continuous sources - made up of radiation of all wavelengths within the spectral region
• Line sources - consist of one or more very narrow bands (<0.01 nm) of

  radiation of known wavelength
• What are the important properties of a source?

  Brightness

  Line width

  Background

  Stability

  Lifetime
• Photometers

  Simple instruments that use filters to select

  wavelength. They can only detect a single wavelength

  at a time, have a high throughput energy due to the

  simple optics (good S/N), and are inexpensive.
• Spectrophotometers

  Instruments that contain a monochromator or

  dispersive element that allow them to scan various

  wavelengths. More expensive than photometers and

  usually have a lower S/N due to the more complex

  optics.
• Photometers

  Simple instruments that use filters to select

  wavelength. They can only detect a single wavelength

  at a time, have a high throughput energy due to the

  simple optics (good S/N), and are inexpensive.
• Spectrometers

  A monochromator equipped with a fixed slit at the

  focal plane.
• Spectrophotometers

  A spectrometer equipped with a phototransducer at

  the exit slit.
• Early spectrophotometers

  used prisms

  quartz for UV

  glass for vis and IR
• Prism - a transparent,

  prism-shaped solid

  that disperses

  polychromatic

  radiation into its

  component

  wavelengths by

  refraction
• Diffraction gratings:

  • made by drawing lines on a

  glass with a diamond stylus
• Grating - consists of a

  polished surface with

  a series of lines etched

  into it that is used to

  disperse

  polychromatic

  radiation by diffraction
• Refraction occurs when a

  wave crosses a boundary

  from one medium to another.

  A wave entering a medium at

  an angle will change

  direction.
• Diffraction refers to the

  "bending of waves around an

  edge" of an object. Diffraction

  depends on the size of the

  object relative to the

  wavelength of the wave.
• Phototubes

  • a device that indicates the existence of same

  physical phenomenon
• Detector

  • a device that indicates the existence of same

  physical phenomenon
• Transducer

  • a special type of detector that converts signals

  such as light intensity, pH, mass, and

  temperature into electrical signals that can be

  subsequently amplified, manipulated, and

  finally converted into numbers that are related

  to the magnitude of the original signal
• Filters operate by absorbing all but a restricted

  band of radiation from a continuum source
• Absorption Filters (Vis)

  • usually consist of a

  colored glass plate

  that removes part of

  the incident radiation

  by absorption to give a

  band of about 30 to

  250 nm.
• Absorption Filters (Vis)

  generally less

  expensive and more

  rugged than

  interference filters
• Interference Filters

  (UV and Vis radiation)

  • rely on optical

  interference to

  provide a relatively

  narrow band of

  radiation, typically

  5 to 20 nm.
• Interference Filters

  consists of a very thin layer of

  a transparent dielectric

  material (frequently CaF2 or

  MgF2) coated on both sides

  with a film of metal that is

  thin enough so it transmits

  approximately half of the

  radiation striking it and

  reflects the other half
• Interference Filters

  (UV and Vis radiation)

  • rely on optical

  interference to

  provide a relatively

  narrow band of

  radiation, typically

  5 to 20 nm.
• Interference Filters

  consists of a very thin layer of

  a transparent dielectric

  material (frequently CaF2 or

  MgF2

  ) coated on both sides

  with a film of metal that is

  thin enough so
• Absorption Filters (Vis)

  • usually consist of a

  colored glass plate

  that removes part of

  the incident radiation

  by absorption to give a

  band of about 30 to

  250 nm.

  • generally less

  expensive and more

  rugged than

  interference filters
• Photometers

  Simple instruments that use filters to select

  wavelength. They can only detect a single wavelength

  at a time, have a high throughput energy due to the

  simple optics (good S/N), and are inexpensive.
• Spectrophotometers

  Instruments that contain a monochromator or

  dispersive element that allow them to scan various

  wavelengths. More expensive than photometers and

  usually have a lower S/N due to the more complex

  optics.
• Spectrometers

  A monochromator equipped with a fixed slit at the

  focal plane.