This experiment was the 4th analysis of a solid sample from Mars. It
is known as Rocknest 4. It revealed the continued presence of the
derivatization reagent, N-methyl-N-tert-butyldimethylsilyl-
trifluoroacetamide (MBSTFA), in the sampling handling system.
For estimation of abundances of volatile compounds detected in EGA,
the background was subtracted as a constant value, typically early in
the preheat (~7300-7400 sec). Exceptions to this were
some peaks contributing to methylene chloride that also contribute to
SO2, for which backgrounds were taken right before the methylene
chloride peak, and the bisilylated water product of MTBSTFA (1,3-bis
(1,1-dimethylethyl)-1,1,3,3-tetramethyldisiloxane), for which the
background was taken after the peak. Uncertainties in abundances,
deriving from statistical noise, background subtraction, calibration
factors, assumptions regarding ionization cross-sections for the
relevant compounds, and isobaric interferences, are estimated at
10-20% of the values.