The paper is freely available from the Proceedings of the National Academy of Sciences web site:

Chemistry
The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results.
( astrobiology | detection of organics | search for martian life | extreme environments | deserts )
Rafael Navarro-González *, Karina F. Navarro *, José de la Rosa *, Enrique Iñiguez *, Paola Molina *, Luis D. Miranda , Pedro Morales , Edith Cienfuegos , Patrice Coll ¶, François Raulin ¶, Ricardo Amils ||, and Christopher P. McKay **
Published online before print October 23, 2006
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0604210103
OPEN ACCESS ARTICLE
http://www.pnas.org/cgi/content/abstract/0604210103v1

From the abstract:

"In the Antarctic Dry Valleys and the Atacama and Libyan Deserts we find 10-90 µg of refractory or graphitic carbon per gram of soil, which would have been undetectable by the Viking TV-GC-MS. In iron-containing soils (jarosites from Rio Tinto and Panoche Valley) and the Mars simulant (palogonite), oxidation of the organic material to carbon dioxide (CO2) by iron oxides and/or their salts drastically attenuates the detection of organics. The release of 50-700 ppm of CO2 by TV-GC-MS in the Viking analysis may indicate that an oxidation of organic material took place. Therefore, the martian surface could have several orders of magnitude more organics than the stated Viking detection limit."{emphasis added}

Interesting!

Bob Clark