Uv – Visible Spectrophotometer.HARIS
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Uv – Visible Spectrophotometer.HARIS






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Uv – Visible Spectrophotometer.HARIS Uv – Visible Spectrophotometer.HARIS Presentation Transcript

  • Spectrophotometer
    • • Measures the light that passes through a liquid sample
    • • Spectrophotometer gives readings in Percent Transmittance (%T) and in Absorbance (A)
  • The Electromagnetic Spectrum  = c /  E = h 
  • Absorbance and Complementary Colors
  • I o I Cell with Pathlength, b, containing solution light source detector blank where I o = I concentration 2 concentration 1 b with sample I < I o The process of light being absorbed by a solution As concentration increased, less light was transmitted (more light absorbed).
    • The law states that the amount of light absorbed by a solution (colored) is proportional to the concentration of the absorbing substance and to the thickness of the absorbing material (path length). Absorbance is also called optical density
    • A = abc
    • where a – molar absorptivity, b – pathlength, and c – molar concentration
  • Some terminology
    • I – intensity where I o is initial intensity
    • T – transmission or %T = 100 x T
    • (absorption: Abs = 1 – T or %Abs = 100 - %T)
    • T = I/ I o
    • A – absorbance
    • A = - log T = -log I/ I o
    • The blank contains all substances expect the analyte.
    • Is used to set the absorbance to zero:
    • A blank = 0
    • This removes any absorption of light due to these substances and the cell.
    • All measured absorbance is due to analyte.
    The Blank
  • Conventional Spectrophotometer 1. A stable and cheap energy source. 2. A monochromator to break the polychromatic radiation into component and wavelength/bands of wave length. 3. Transparent vessels (cuvettes) to hold the sample. 4. A photo sensitive detector and associated amplifier and recorder
  • Conventional Spectrophotometer Optical system of a split-beam spectrophotometer
  • LIGHT SOURCES   UV Spectrophotometer 1. Hydrogen Gas Lamp 2. Mercury Lamp Visible Spectrophotometer 1. Tungsten Lamp IR Spectrophotometer 1. Carborundum (SIC)
  • Light Source
    • Deuterium Arc Lamp
    • UV Region
    • Wavelength Range :
    • 190~420nm
    • Tungsten Lamp
    • Wavelength Range : Part of the UV and the whole of the Visible
    • range ( 약 350 ~ 2,500nm)
    • Xenon Lamp
    • Wavelength Range : 190~800nm
  • Monochromator
    • Accepts polychromatic input light from a lamp and outputs monochromatic light
    • Components : Entrance slit, Dispersion device, Exit slit.
    • The resolving element are of two kinds namely,
    • prisms and diffraction gratings. Simple glass prisms are used for visible range. For UV region silica, fused silica or quartz prism is used. Fluorite is used in vaccum UV range.
    • Gratings are often used in the monochromators of spectrophotometers operating in UV, visible and infra red regions. Their resolving power is far superior to that of prisms & they yield a linear resolution of spectrum.
  • Dispersion Devices
    • Non-linear dispersion
    • Temperature sensitive
    • Linear Dispersion
    • Different orders
  • CELLS UV Spectrophotometer Quartz (crystalline silica)   Visible Spectrophotometer Glass   IR Spectrophotometer NaCl
  • Cell Types I Open-topped rectangular standard cell (a) and apertured cell (b) for limited sample volume
  • Cell Types II Micro cell (a) for very small volumes and flow-through cell (b) for automated applications
  • Detection Devices
    • Most detectors depend on the photoelectric effect, where incident light photons) liberates electrons from a metal or other material surface.
    • Important requirements for a detector
    • (1)high sensitivity to allow the detection of low levels of radiant energy,
    • (2)short response time,
    • (3)long term stability, and
    • (4)an electronic signal which is easily amplified for typical read out apparatus, Ultraviolet and visible radiation detectors are photocells, phototubes and photo multiplier tubes.
  • Photomultiplier Tube Detector Anode
    • High sensitivity at
    • low light levels
    • Cathode material
    • determines spectral sensitivity
    • Good signal/noise
    • Shock sensitive
  • Amplification and Readout
    • Radiation detectors generate electronic signals which are proportional to the transmitter light.
    • These signals need to be translated to a form that is easy to interpret.
    • This is accomplished by using amplifiers, ammeters, potentiometers, and potentiometric recorders.
    • 1. Qualitative Analysis
    • 2. Quantitative Analysis
    • 3. Molecular weight determination
    • 4. Study of cis-trans Isomerism
    • 5. Other Physiochemical studies
    • 6. Control of Purification
    • 7. Difference Spectroscopy
    • 8. Turbidimetry
    Applications of UV - Visible Spectroscopy
    • Thank You