Spetrochemical Analysis: Instrument components
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Analytical Chemistry Spetrochemical Analysis Instruments for Optical Spectrometry Instrument Components
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Spetrochemical Analysis: Instrument components
- 1. Instrument Components © Glydenne Glaire P. Gayam
- 2. 1. source of radiant energy 2. wavelength selector 3. sample container 4. detector 5. signal processor and readout © Glydenne Glaire P. Gayam
- 3. © Glydenne Glaire P. Gayam
- 4. Two wavelength selectors are needed to select the excitation and the emission wavelengths. The selected source radiation is incident on the sample and the radiation emitted is measured, usually at right angles to avoid scattering. © Glydenne Glaire P. Gayam
- 5. A source of thermal energy, such as a flame, produces an analyte vapor that emits radiation that is isolated by the wavelengths selector and converted to an electrical signal by the detector. © Glydenne Glaire P. Gayam
- 6. Cells Windows Lenses Wavelength Dispersing Element © Glydenne Glaire P. Gayam
- 7. I. Optical Materials Transmittance ranges for various optical materials. © Glydenne Glaire P. Gayam
- 8. I. Optical Materials Silicate glass: Visible region Fused silica or quartz: UV region (<380nm) Halide salts: IR region © Glydenne Glaire P. Gayam
- 9. 1. Continuum sources • emit radiation that changes in intensity only slowly as a function of wavelength • Widely use in absorption and fluorescence spectroscopy for UV region 2. Line sources • emit a limited number of bands of radiation, each of which spans a very limited range of wavelength • Widely used in atomic absorption spectroscopy and in molecular florescence spectroscopy • Eg. Hg and Na vapors lamps •Generate a beam of radiation with sufficient and stable power © Glydenne Glaire P. Gayam
- 10. The spectrum of a continuum source (a) is much broader than that of a line source (b). © Glydenne Glaire P. Gayam
- 11. Source Wavelength Region, nm Type of Spectroscopy Xenon arc lamps 250-600 Molecular Fluorescence H2 and D2 lamps 160-380 UV Molecular Absorption Tungsten/Halogen lamp 240-2500 UV/vis/near-IR molecular absorption Tungsten lamp 350-2200 Vis/near-IR molecular absorption Nernst glower 400-20,000 IR molecular absorption Nichrome wire 750-20,000 IR molecular absorption Globar 1200-40,000 IR molecular absorption © Glydenne Glaire P. Gayam
- 12. provides radiation of all wavelength within a particular spectral region. © Glydenne Glaire P. Gayam
- 13. A tungsten lamp of the type used in spectroscopy and its spectrum. Intensity of the tungsten source is usually quite low at wavelengths shorter than about 350 nm. © Glydenne Glaire P. Gayam
- 14. A cylindrical tube (contains deuterium at a low pressure) with a quartz window (the radiation exits) © Glydenne Glaire P. Gayam A deuterium lamp of the type used in spectrophotometers and its spectrum.
- 15. Globar source: 1 - 40 μm (Globar heated to about 1500℃) 5- by 50-mm silicon carbide rod. Nernst glower: a cylinder of zirconium and yttrium oxides. Nichrome wire © Glydenne Glaire P. Gayam
- 16. 1. Monochromators and Polychromators 2. Grating 3. Radiation Filters © Glydenne Glaire P. Gayam - enhance both the selectivity and the sensitivity
- 17. 1. Monochromators and Polychromators • Advantage: the output wavelength can be varied continuously over a considerable spectral range. (the more common type) 2. Grating – disperse radiation into its component wavelengths • Qualitative analysis: narrow slits and minimum effective bandwidths • Quantitative analysis: wider slits permit operation at lower amplification (greater reproductibility © Glydenne Glaire P. Gayam
- 18. 3. Radiation Filters • Advantage: simplicity, ruggedness and cheapness • Interference filter: effective bandwidths of 5 to 20 nm • Dielectric material: CaF2 of MgF2 • Absorption filter: effective bandwidths of 50 to 250 nm © Glydenne Glaire P. Gayam
- 19. detector: indicates the existence of some physical phenomenon. ex: photographic film, pointer of a balance, mercury level in a thermometer, and human eye transducer: converts signals, such as light intensity, pH, mass and temp. into electrical signals that can be subsequently amplified, manipulated and finally converted into numbers proportional to the magnitude of the original signal. © Glydenne Glaire P. Gayam
- 20. Types of Transducers © Glydenne Glaire P. Gayam 1. Photon Detectors • Phototubes • Photomultiplier tubes • Silicon photodiodes • Photoconductive cells 2. Heat Detectors • Thermocouples • Bolometers • Pneumatic cells • Pyroelectric cells
- 21. © Glydenne Glaire P. Gayam Common Detectors for Absorption Spectroscopy Type Wavelength Range, nm Type of Spectroscopy Photon Detectors Phototubes 150-1000 UV/visible and near-IR absorption Photomultiplier tubes 150-1000 UV/visible and near-IR absorption, molecular fluorescence Silicon photodiodes 350-1100 Visible and near-IR absorption Photoconductive cells 1000-50,000 IR absorption Types of Transducers
- 22. © Glydenne Glaire P. Gayam Common Detectors for Absorption Spectroscopy Type Wavelength Range, nm Type of Spectroscopy Heat Detectors Thermocouples 600-20,000 IR absorption Bolometers 600-20,000 IR absorption Pneumatic cells 600-40,000 IR absorption Pyroelectric cells 1000-20,000 IR absorption Types of Transducers
- 23. Sample Containers © Glydenne Glaire P. Gayam Typical examples of commercially available cells for the UV/visible region. Cells or cuvettes: 0.1 to 1-cm path length