Gang Wang Instrumental_Week3_4_5_CH7-2010

Gang Wang Instrumental_Week3_4_5_CH7-2010 - Skoog Chapter 7...

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Skoog–Chapter 7 Components of Optical Instruments y General Design of Optical Instruments y Sources of Radiation y Wavelength Selectors y Sample Containers y Radiation Transducers (Detectors) y Signal Processors and Readouts y Fiber Optics Optical spectroscopic based on 6 phenomena: y Adsorption y Fluorescence y Phosphorescrence y Scattering y Emission y Chemiluminscrence
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Absorption measurements require: 1) source of radiation 2) device for dispersing radiation into component wavelengths 3) a means of putting sample into the optical path, i.e., cell 4) Detector to convert the EM to an electrical signal 5) readout device or circuitry, i.e., meter, computer, recorder, integrator, etc. Block diagram of instrument for absorption Light Source Wavelength Selector Sample Holder Detector Signal Processing Readout Device The location of these can be reversed Range of λ ’s Narrow Band of λ ’s Æ I o Transmitted Intensity Æ I Here the wavelength of interest is selected first, then passed through the sample
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Block diagram of instrument for absorption Light Source Wavelength Selector Sample Holder Detector Signal Processing Readout Device Range of λ ’s Transmitted I at all λ ’s Selected λ Band Æ I Here all wavelengths pass through the sample together, then the wavelength of interest is selected and detected Block diagram of instrument for emission i.e., phosphorescence Light Source Wavelength Selector Sample Holder Detector Signal Processing Readout Device Range of λ ’s Emitted λ Spectrum Æ I Selected λ Band Æ I Wavelength Selector Selected λ Band for Excitation Æ I o
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Emission measurements require: 1) means of exciting emission i.e., way of populating upper energy level which spontaneously emits 2) device for dispersing radiation into component wavelengths 3) a means of putting sample into the optical path, i.e., cell 4) Detector to convert the EM to an electrical signal 5) readout device or circuitry, i.e., meter, computer, recorder, integrator, etc. The requirements for the various components used in different instruments change with the type of spectroscopy as well as for different kinds of measurements within a type of spectroscopy We will consider the components separately then combine them to make the overall instrument And finally look at the measurements with regard to theory and practice Radiation Source Sufficient energy for easy detection and measurement Stable for a reasonable period Regulated power source (radiant power source varies with voltage power supply) Double beam design, detection intensity of two beams simultaneously
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Sources –important characteristics 1) Spectral distribution i.e., intensity vs. λ (continuum vs. line sources) 2) Intensity 3) Stability–short term fluctuations (noise), long term drift 4) Cost 5) Lifetime 6) Geometry–match to dispersion device I) CONTINUUM SOURCES Absorption and Fluorescence spectroscopy UV region deuterium High pressure gas filled lamp contains argon,
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Gang Wang Instrumental_Week3_4_5_CH7-2010 - Skoog Chapter 7...

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