Lecture_overheads_-_Ch19

Lecture_overheads_-_Ch19 - CHEM 321 Quantitative Analysis...

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CHEM 321 – Quantitative Analysis Ch. 19 – Spectrophotometers Interaction of Light with Matter 19-1 Lamps and Lasers (light sources) Continuous (broadband) sources Line sources (lasers) 19-2 Monochromators Filters Gratings Sample Cells (from prior chapter) 19-3 Detectors Photomultiplier tubes (PMTs) Array detectors Types of UV/Vis Spectrophotometers Other Spectroscopy Applications
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eraction of light with matter hen light “shines” on sample, it can be flected at any surface or phase transition (cuvette/solution) attered by surfaces (scratches or nonuniformities), dust or suspended particles, and molecules (Raman effect) ansmitted passes entirely through sample sorbed related to transmittance (A = -log T) use this absorbance to compute concentration (A = ε bc) a spectrophotometric analysis, we attempt to MINIMIZE losses of light due to reflection and scattering and focus on absorbance of analyte at its characteristic λ e must also select a source, wavelength separation device, sample cell, and detector that are APPROPRIATE for the λ range of interest
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19-1 Lamps and Lasers (Sources of Light) Continuous (broadband) sources Laser (line) sources: Must choose a light source that is appropriate for the region of the electromagnetic spectrum you’re working in (i.e., one that EMITS at your λ ’s of interest) Wavelength (nm) P (W) P (W) Wavelength (nm)
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Continuum Sources Spectra of Blackbody Radiation Sources ( note as T↑, λ max ) Spectra of Tungsten lamp (Visible source) and Deuterium (D 2 ) lamp (UV source) UV sources D 2 lamp, Xe lamp Visible sources Tungsten lamp IR sources Nernst glower (rare earth oxide) Nichrome wire (NiCr) globar (SiC rod heated to 1500 K)
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Laser Sources ADVANTAGES Extremely bright (brighter than the Sun’s λ max in yellow region, intensity “folded” into narrow λ range)
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Lecture_overheads_-_Ch19 - CHEM 321 Quantitative Analysis...

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