  Numerous studies have been carried out to characterize the chemical
composition of laboratory analogues of Titan aerosols (tholins), but their
molecular composition as well as their structure are still poorly known. If
pyrolysis gas chromatography mass spectrometry (pyr-GCMS) has been used for
years to give clues about this composition, the highly disparate results
obtained can be attributed to the analytical conditions used and/or to
differences in the nature of the analogues studied. In order to have a better
description of Titan tholins molecular composition, we led a systematic
analysis of these materials using pyr-GCMS with two major objectives: (i)
exploring the analytical parameters to estimate the biases this technique can
induce and to find an optimum for analyses allowing the detection of a wide
range of compounds and thus a characterization of the tholins composition as
comprehensive as possible, and (ii) highlighting the role of the CH4 ratio in
the gaseous reactive medium on the tholins molecular structure. With this aim,
we used a radio-frequency plasma discharge to synthetize tholins with different
concentrations of CH4 diluted in N2. The samples were systematically pyrolyzed
from 200 to 600{\deg}C. The extracted gases were then analyzed by GCMS for
their molecular identification.
