Photoacoustic Spectroscopy – a versatile spectroscopic tool

Photoacoustic Spectroscopy – a versatile spectroscopic tool
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Photoacoustic sample cell schematic (Image Courtesy : http://www.shimadzu.com/)

Photoacoustic spectroscopy makes your analysis a lot simpler than other conventional spectroscopic techniques and offers potential saving of your valuable laboratory time. Let us first begin with the advantages offered by the technique.

Benefits over other spectroscopic techniques:

  • The technique is non-destructive. No need for sample preparation by dissolving in a solvent or mixing in another solid powder matrix.
  • Absorbance signals are not affected by scattering by sample media
  • Spectroscopic studies can be carried out over spectral regions covering UV, visible and infrared light
  • Samples can be analyzed in different states such as gels, amorphous powders, chips or large sized objects which are otherwise not conducive for analysis by reflective or transmission spectroscopic modes.
  • Depth profiling is the biggest advantage of photoacoustic spectroscopy. It facilitates characterization of an object or sample through depth profiling and profiling of multi layered sheets

Basics of Photoacoustic spectroscopy

Photoacoustic spectroscopy is a unique spectroscopic technique which makes use of both light and sound energy. Like other conventional techniques absorption of electromagnetic radiation takes place by the analyte molecules. The absorbed energy results in local heating of the sample. Due to the local heating pressure changes take place which can be detected as sound waves by microphone-based detection. Alternately the incoming light beam is modulated and the resulting pressure pulses can be detected using piezoelectric devices.

Applications

Gases

Increase of temperature in a constant volume gas cell results in increased pressure. Modulation of incoming light beam frequencies creates pressure pulses which result in sound waves.

Laser sources have been used effectively for detection of trace concentrations of gaseous mixture components down to ppt levels. The applications range from environmental gas monitoring to online monitoring of gases in process streams.

Solids and Liquids

Photoacoustic spectroscopy is particularly useful for samples which require tedious sample preparation such as polymeric multi-layered sheets, gels, amorphous powders, granules, etc. The technique is also used for spectroscopic studies on biological samples such as lipids, blood, skin, tumors and proteins. Conventional spectroscopic applications on such molecules are plagued with potential interferences due to light scattering by such molecules.

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