Review of the controversy about the sensitivity of the Viking GCMS sent to Mars to detect organic molecules:

Secrets of the Martian soil.
Corinna Wu
Nature, 16 Aug 2007, p 742-744 v 448.
"Navarro-González was inspired to revisit the Viking tests for organic molecules after the exploratory rover Opportunity discovered jarosite, a hydrated iron sulphate that forms in the presence of water, on Mars in 2004. Studying jarosite-containing soils in the Rio Tinto area of Spain he found that getting organic material out using chemical approaches was relatively easy — but getting it out just by heating was not. “When I repeated the Viking experiments, “ he says, “I was surprised to see that despite the huge amount of organic matter present, there was virtually no detection of organics in the sediments. This was quite strange.” Independently, McKay had been doing research on soils from the Atacama desert in Chile, and had also started to suspect that the Viking experiments weren’t telling the whole story. Alison Skelley, a graduate student at the University of California, Berkeley, had asked McKay to review a paper on a device she had developed for detecting amino acids in soil3.
McKay found the paper striking. “It found that there were a thousand times more amino acids released by chemical extraction than pyrolysis” — the heating method used by the Viking experiments. Then McKay says, “Within a month, Rafael told me about his puzzling result with the jarosite. That’s when I suggested that we ought to see if this effect was widespread.”"
...
"Heated debate."
"Navarro-González and McKay think that during the heating step of the Viking experiment, any organics given off at moderate temperatures would have been turned into CO2 before they reached the GC-MS, thanks to catalytic iron compounds in the Martian soil. “We suggest that a small portion [of the carbon dioxide seen by the Viking experiments] could have resulted from the oxidation of organics,” says Navarro-González. “Even if it’s just a small percentage, this could mean levels of organics on the surface of Mars a thousand times higher than expected.”"
http://www.mediabistro.com/portfolios/samples_files/f_H_nfRIm0m4VCEEe4129Gees.pdf

Bob Clark