I've been informed that not only do the iron compounds known to exist on Mars catalyze the breakdown of organics at high temperatures but so also does perchlorate. This is consistent with what was said about perchlorate in the Mars Phoenix news conference that it was a weak oxidant but becomes more active at high temperatures.
Then a breakdown in the TEGA instrument of organics could be coming from two sources making their detection more difficult. Yet the detection of evolved CO2 only at high temperatures in TEGA tantalizing suggests they might be there.
Because of the importance of detecting organics on Mars means should be investigated for mitigating the decomposing effects of the minerals in the soil on organics. One possibility would be by dissolving the iron compounds and perchlorate in liquid water, if a sample could be delivered to TEGA with a sizable ice content. Jarosite a ferric sulfate shown to decompose organics was proven by the MER rovers to exist on Mars and is soluble in water, as is also perchlorate. But when you heated the sample to detect the organics the water would evaporate and the iron compounds and perchlorate would precipitate out again so would presumably still have their oxidizing effect on the organics.
But what if the iron compounds and perchlorate could be separated from the organics? MER rover scientists during the discovery by Opportunity of sedimentary deposits mentioned there appeared to be an "evaporation sequence" where different minerals precipitated out at different times. Did this mean they were present in separated layers?
If so, then perhaps by slow heating of the water in the TEGA sample the iron compounds and the perchlorate could be made to precipitate out in separate well defined layers that would allow at least some of the organics not to come in contact with those layers.

Bob Clark