Spec20 Instrument Sample holder cover Amplifier control knob

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

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

Schematic representation of a spectrophotometer I Io Monochromator Light Source (1) Detector Meter Sample cell (2) (5) (4) (3) 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. Meter 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. Wavelength control Wavelength scale Sample-holder Light control Zero adjust and power control

Absorbance of Chlorophyll 1. 5 Frequency (Hz) 1026 cosmic rays 1. 2 10 -8 1022 1024 gamma rays 10 -4 10 -6 1020 1018 x-rays 10 -2 1016 ultraviolet 1 102 1010 1014 106 108 infraradio radar tele- radio red (microwave) vision 104 106 108 1010 1012 104 power transmission 1014 1016 Absorbance Wavelength (nm) UV 0. 9 Violet 400 nm Blue Green Yellow Orange Red 700 nm 600 nm 500 nm 0. 6 0. 3 0. 0 300 400 500 600 Wavelength (nm) 700 800 1 Near Infrared

Amount absorbed 400 663 nm 500 600 Wavelength (nm) Kelter, Carr, Scott, , Chemistry: A World of Choices 1999, page 480 700

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