Enhanced selectivity and sensitivity in UV analysis of volatile organic compounds

Karsten Sassenscheid; Ulrich Klocke; Gerhard Schmidtke; Maurus Tacke

doi:10.1117/12.336860

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18 January 1999 Enhanced selectivity and sensitivity in UV analysis of volatile organic compounds

Karsten Sassenscheid, Ulrich Klocke, Gerhard Schmidtke, Maurus Tacke

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Proceedings Volume 3533, Air Monitoring and Detection of Chemical and Biological Agents; (1999) https://doi.org/10.1117/12.336860
Event: Photonics East (ISAM, VVDC, IEMB), 1998, Boston, MA, United States

Abstract

Sensitivity and selectivity requirements in on-line trace gas analysis of volatile organic compounds often cannot be satisfied. Due to their photochemical Ozone creation potential there is a strong demand for fast and accurate measurement techniques. Although many spectroscopy techniques are quite sensitive to individual components they often suffer from a lack of selectivity between similar spectroscopic compounds. We report on a special system with optical derivative generation. Gas analysis is performed by means of transmission spectroscopy in the UV. A deuterium lamp is used as light source. Due to the strong UV- absorption bands of organic compounds, sensitive detection is typical. Spectroscopic filtering is provided by a special grating monochromator. The grating is mounted on a galvanometer scanner, allowing a computer controlled wavelength scan and modulation. Analog signal processing is performed using lock-in-amplifier techniques. This form of detection of derivative spectra with a movable optical component is the origin of the term Dynamic Derivative Spectroscopy (DDS). Combined with the use of a White-Cell - providing an optical path length up to 100m - very high sensitivity is achieve. The adjustment of the wavelength- modulation amplitude, as a significant parameter of DDS, can be optimized to the gas of interest due to the individual and characteristic slopes and curvatures of the gaseous absorption bands. Selectivity is improved separating spectral features in overlapping bands. We discuss the theoretical background and present experimental data on system performance. The impact of wavelength modulation as a powerful tool is demonstrated, sensitive and fast multicomponent measurements of volatile organic compounds are presented.

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Karsten Sassenscheid, Ulrich Klocke, Gerhard Schmidtke, and Maurus Tacke "Enhanced selectivity and sensitivity in UV analysis of volatile organic compounds", Proc. SPIE 3533, Air Monitoring and Detection of Chemical and Biological Agents, (18 January 1999); https://doi.org/10.1117/12.336860

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