Vol. 25 No. 5
September-October 2003

Critical Assessment: Use of Supersonic Jet Spectrometry for Complex Mixture Analysis (IUPAC Technical Report)

T. Imasaka, D. S. Moore, and T. Vo-Dinh

Pure and Applied Chemistry
Vol. 75, No.7, pp. 975-991 (2003)

A typical analytical instrument for supersonic jet spectrometry, which allows detection by fluorescence excitation /emission and multiphoton ionization/mass spectrometries simultaneously. Source: T. Imasaka, M. Hozumi, N. Ishibashi. Anal. Chem. 64, 2206 (1992). (Larger view)

Numerous chemical substances are present in an authentic sample. Therefore, it is necessary to develop an analytical instrument with high selectivity. However, absorption or excitation/fluorescence spectrometry currently used for analysis of the sample in the condensed phase at room temperature provides a broad band in the spectrum. Therefore, it is difficult to apply it to complex mixture analysis.

When the analyte molecule is cooled to a temperature of a few K using supersonic jet expansion into a vacuum, a molecule exists in the lowest vibrational level of the ground electronic state and is isolated at collision-free conditions. The absorption or excitation/ fluorescence spectrum is then greatly simplified when transitions occur from this single vibrational level to a limited number of vibrational levels in the excited electronic state. This method, called supersonic jet spectrometry, is a powerful analytical technique because of its high selectivity, since the chemical species can be accurately identified and selectively quantified using the sharp spectral features even for large molecules.

Supersonic jet spectrometry has distinct advantages over other low-temperature spectrometries, in that it can be combined with gas phase separation and detection techniques such as chromatography or mass spectrometry. Therefore, this spectrometric technique can be used as a versatile analytical means, not only for basic research on single standard molecules but also for practical trace analysis of chemical species in multicomponent samples (e.g., in biological monitoring or in environmental monitoring).

In this critical assessment basic operational principles and analytical instrumentation are introduced in addition to various applications to polycyclic aromatic hydrocarbons, polymer decomposition products, and chemically hazardous compounds such as dioxins. Several approaches for assignment of the chemical species are also provided, which involve the use of the data of the 0-0 transition for ca. 300 organic compounds and of the theoretical techniques using molecular orbital calculation and fuzzy recognition of the spectral feature.

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