Instrumentation in infrared (IR) spectroscopy

Instrumentation in infrared (IR) spectroscopy includes source, monochromator, sample holder, and detector.

Instrumentation in infrared (IR) spectroscopy

• A spectrometer measures light properties across specific electromagnetic spectrum ranges, aiding in material identification.
• Key components include the source, wavelength selectors, and detectors.

1. Sources of Radiation:

   • Provide stable, long-lasting IR radiation over the desired wavelength range.
     1. Globar: Silicon carbide rod emitting in the mid-IR region; stable spectral radiance.
     2. Nernst Glower: Ceramic rod made of rare earth oxides; emits in the mid-IR, with radiance increasing with wavelength.
     3. Tungsten Filament: Covers near-IR and visible regions with broad emission.
     4. Mercury Arc Lamp: Emits radiation in the far-IR region.

2. Wavelength Selectors:

   • Separate broad-spectrum radiation into specific frequencies.
     1. Monochromators: Use prisms or gratings to disperse radiation by bending different wavelengths differently.
     2. Interferometers: In FTIR instruments, they split and recombine beams to produce an interferogram, which is Fourier transformed to generate the spectrum.

3. Detectors:

   • Convert transmitted or reflected IR radiation into an electrical signal for analysis.
     1. Golay Cell:
        • Thermal detector using gas pressure changes due to IR heating.
        • Application: Wide frequency range, fast response (used in FTIR).
     2. Bolometer:
        • Detects resistance changes in blackened platinum or gold strips upon IR absorption.
        • Application: High sensitivity for far-IR detection.
     3. Thermocouple:
        • Two joined metals produce a voltage when heated by IR radiation.
        • Application: Moderate sensitivity, suitable for mid-IR.
     4. Thermistor:
        • Semiconductors whose resistance changes with temperature upon IR exposure.
        • Application: Higher sensitivity for mid-IR.
     5. Pyroelectric Detectors (e.g., DTGS):
        • Generate voltage with temperature changes due to IR heating.
        • Application: Broad spectral response, ideal for FTIR instruments, operates at room temperature.

These components collectively ensure precise and reliable IR spectroscopic analysis across various applications.

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