Analytical Chemistry Spetrochemical Analysis Instruments for Optical Spectrometry Instrument Components

1. Instrument
Components
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2. 1. source of radiant energy
2. wavelength selector
3. sample container
4. detector
5. signal processor and readout
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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.
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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.
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6. Cells
Windows
Lenses
Wavelength Dispersing Element
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7. I. Optical Materials
Transmittance ranges for various optical materials.
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8. I. Optical Materials
Silicate glass: Visible region
Fused silica or quartz: UV region (<380nm)
Halide salts: IR region
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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
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10. The spectrum of a continuum source (a) is much
broader than that of a line source (b).
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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
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12. provides radiation of all wavelength within a
particular spectral region.
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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.
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14. A cylindrical tube
(contains deuterium at
a low pressure) with a
quartz window (the
radiation exits)
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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
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16. 1. Monochromators and Polychromators
2. Grating
3. Radiation Filters
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- 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
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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
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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.
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20. Types of Transducers
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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
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Typical examples of commercially available cells for the UV/visible region.
Cells or cuvettes: 0.1 to 1-cm path length