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Spec-20 Instrument

Spec-20 Instrument. Wavelength control knob. Light control knob. Amplifier control knob. Sample holder cover. Meter. Wavelength control. Wavelength scale. Sample-holder. Light control. Zero adjust and power control. Spec-20 Absorbance. Insert Photograph Spec-20.

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Spec-20 Instrument

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  1. Spec-20 Instrument Wavelength control knob Light control knob Amplifier control knob Sample holder cover

  2. Meter Wavelength control Wavelength scale Sample-holder Light control Zero adjust and power control Spec-20 Absorbance Insert Photograph Spec-20 100 % Absorbance 0 % Transmittance Absorbance 0 % Absorbance 100 % Transmittance l (wavelength)

  3. Meter Wavelength control Wavelength scale Sample-holder Light control Zero adjust and power control Schematic representation of a spectrophotometer I Io Monochromator Detector Meter Light Source (1) Sample cell (3) (2) (5) (4) A spectrophotometer is an instrument that measures the fraction (I/Io) of an incident beam of light (Io) which is transmitted (I) by a sample at a particular wavelength. For a given substance, the amount of light absorbed depends on: a) the concentration; b) the cell or path length; c) the wavelength of light; and d) the solvent.

  4. Frequency (Hz) 1 102 106 104 1010 108 1022 1020 1018 1016 1014 1026 1024 infra- red radio (microwave) radar tele- vision radio power transmission gamma rays x-rays ultra- violet cosmic rays 1016 1012 1014 106 108 1010 10-4 10-2 1 102 104 10-8 10-6 Wavelength (nm) Near Infrared UV Yellow Orange Red Violet Blue Green 700 nm 600 nm 500 nm 400 nm Absorbance of Chlorophyll 1.5 1.2 0.9 Absorbance 0.6 0.3 0.0 300 400 500 600 700 800 Wavelength (nm)

  5. Amount absorbed 663 nm 400 500 600 700 Wavelength (nm) Kelter, Carr, Scott, , Chemistry: A World of Choices1999, page 480

  6. Calibration Curve (fixed wavelength) 100 % Absorbance 0 % Transmittance out of linear range (too concentrated) ? Absorbance 0 % Absorbance 100 % Transmittance x 2 Concentration Dilute sample with water 50:50. Run sample, read concentration.

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