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Laboratory
for ChemoMetrics,
Vienna (Austria) MS - Chemometrics - COSIMA |
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Summary of Results: Comparison PDMS - SIMS |
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[ Aims | People | Results | Presentations | Pictures | ROSETTA | COSIMA Instrument
| Comet
Wirtanen | Literature
] |
Last update 2000-12-04 |
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No cometary material has yet
been brought back to Earth under controlled conditions. No SIMS data (Secondary
Ion Mass Spectrometry, used by COSIMA) are available from substances
relevant to cometary material. So, mass spectral data
used for chemometric investigations have been measured on a Plasma
Desorption Mass Spectrometer (PDMS, 252-Cf ionization) in the lab
of E.R. Schmid. |
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The 63 reference
substances measured have molecular formulas C2-14H3-17N0-6O0-6
with molecular masses between 83 and 214; included are N-heterocycles,
substituted (N-)aromatic rings, and dicarboxylic acids. |
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Although the energies of
the impacting particles are very different in SIMS and PDMS instruments the resulting
mass spectra (in positive as well as in negative ion mode) are similar. To
demonstrate this fact the PDMS and the SIMS data from four
selected compounds have been measured and compared [more
details, example]. The similarity of both methods
makes PDMS data suitable for testing chemometric methods considered for
COSIMA. |
More details
Organic substances in
cometary grains: Comparison of secondary ion mass spectral data and
Californium-252 plasma desorption data from reference compounds.
K. Varmuza, W. Werther, F. R. Krueger, J. Kissel, and E. R. Schmid:
Int. J. Mass Spectrom. 189, 79-92 (1999)
Excerpt:
The spacecraft ROSETTA of the European Space Agency will carry a time-of-flight (TOF) secondary ion mass spectrometer (SIMS) to comet 46P/Wirtanen. It is planned to analyze in situ the organic and inorganic components of collected cometary grains. Empirical information about the organic constituents of cometary dust is solely based on measurements of ions produced by the high-speed impact of cometary dust particles as obtained in three experiments near comet P/Halley. The intimate mixture of organic and inorganic material in cometary grains is considered to have been involved in the development of life on earth.
Because only little systematic knowledge is available about relationships between SIMS data of organic compounds and chemical structures four reference compounds have been investigated. Secondary ion mass spectra (SIMS) and 252-Cf plasma desorption mass spectra (PDMS) of two carboxylic acids and two purine nucleobases have been compared. The obtained results demonstrate that the positive ion mass spectra as well as the negative ion mass spectra are very similar in SIMS and PDMS.
The principal characteristics of these spectra are the formation of quasimolecular ions [M+H]+ and [M-H]- and the loss of small molecules giving rise mainly of nonradical fragment ions. A set of rules has been formulated by F.R. Krueger (Darmstadt, Germany) for typical ion production processes which are involved in these techniques. These rules are considered to be helpful for the definition of numerical spectral features that are necessary for the application of multivariate data analysis methods.
The comparison of SIMS and PDMS data demonstrates that PDMS data are suitable for testing chemometric methods that will help in the automatic data evaluation on board of COSIMA.
Example
Adenine: Positive ion mass spectra for SIMS and PDMS
Adenine: Negative ion mass spectra for SIMS and PDMS
Adenine: EI mass spectrum
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[ Aims | People | Results | Presentations | Pictures | ROSETTA | COSIMA Instrument
| Comet
Wirtanen | Literature
] |
Last update 2000-12-04 |
