Biology 2290F/G Lecture Notes - Lecture 4: Attenuation Coefficient, Dichlorophenolindophenol, Diffraction Grating
28 Dec 2017
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Lamp: supplies radiant energy of wavelengths 340 900 nm: light focuses onto diffraction grating. Diffraction grating: splits light into its component wavelengths: changing its position changes the wavelength of light that passes through the slit. Phototube: transduces light energy transmitted by the sample into electric current. The amount of light transmitted (not absorbed) by a sample is compared with a reference blank to determine how much light has been absorbed by sample. The spectrophotometer does not measure absorbance, it measures transmittance. Transmittance (t) is the fraction of the incident light that passes through the sample. **where io = radiant power of incident light** **where i = radiant power of light passing through sample** Absorbance (a) is the amount of light absorbed by the sample. La(cid:373)(cid:271)ert"s law: for a thin layer of sample, the same proportion of light is absorbed regardless of the radiant power of the incident light (io)
