On the ability of the Viking gas chromatograph–mass spectrometer to detect organic matter

doi:10.1073/pnas.0703732104

On the ability of the Viking gas chromatograph–mass spectrometer to detect organic matter

Klaus Biemann*

Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139

Contributed by Klaus Biemann, April 23, 2007 (received for review March 30, 2007)

Abstract

A recent paper by Navarro-Gonzalez et al. [Navarro-Gonzalez R, Navarro KF, de la Rosa J, Iniguez E, Molina P, Miranda LD, Morales P, Cienfuegos E, Coll P, Raulin F, et al. (2006) Proc Natl Acad Sci USA 103:16089–16094] claims to show that the Viking GCMS (gas chromatograph–mass spectrometer) experiment, which carried out a search for organic matter at the surface of Mars in 1976, “may have been blind to low levels of organics.” To rebut this assertion, the Viking experiment, test data, and results on Mars are reviewed, and the fallacies in the design, execution, and interpretation of the new experiments presented by Navarro-Gonzalez et al. are critically examined.

Footnotes

*E-mail: kbiemann{at}mit.edu
Author contributions: K.B. designed research, performed research, analyzed data, and wrote the paper.
The author declares no conflict of interest.
↵ † For molecules containing only one or two carbon atoms and coeluting with water or carbon dioxide, the detection limit was in the ppm range.
↵ ‡ Most of the more significant comments and questions received no response and are thus raised herein.
↵ § The assumption that benzene is always the major pyrolysis product is naïve. It would have been more convincing to present the entire chromatogram, including amounts detected, of at least a few representative experiments as it was done for the Viking GCMS tests (2, 3).
↵ ¶ The chemical equation for the oxidation of HCOOH with KMnO₄ shown in the on-line supporting materials and methods of ref. 18 is not balanced, i.e., incorrect; the use of formic acid, in which the carbon is already highly oxidized, is also not appropriate in the context of a TOM analysis.
↵ ‖ This was pointed out to Dr. Navarro-Gonzalez in the comments on the earlier version of his manuscript, but the statement remained in the abstract.
↵ ** The text of ref. 18 states that a “similar result was obtained at 500°C,” but the extent of oxidation would undoubtedly be lower, and it would have been more appropriate to report these results instead. Furthermore, stearic acid is not a realistic surrogate for the polycyclic aromatic hydrocarbons one expected on Mars from meteorites, the only organic compounds one would expect to find there with any certainty.
↵ †† The model experiment (figure 5 of ref. 18) indicates that 1% and 10% Fe₂O₃ causes oxidation of ≈10% and 40%, respectively, of the organic matter; for Fe₂(SO₄)₃, the values are 35% and 45%. Sulfur represents only 3.1 ± 0.5% of the soil at both Viking landing sites (19). Therefore, iron sulfate must be a minor component, compared with oxide. The presence of free sulfuric acid in the Martian soil is not supported by any data, and it is not realistic to include it in any experiment modeling the Martian soil.
Abbreviations:

GCMS,

gas chromatograph–mass spectrometer;

ppb,

parts per billion;

TOM,

total organic matter.