The concentration and isotopic composition of n-alkanes C1-C5 has revealed as a powerful tool for interpretation of interesting processes in the oil exploration industry, studies of global climate change, oil biodegradation and carbon cycle elucidation. In this context, studies about methane analysis have been distinguished and multiplied due to the important role of C1 in the energy industry and its contribution for the greenhouse effect. The analysis of atmospheric and geological samples is a challenge, since the low concentration limits the use of the conventional GC-IRMS technique (Gas Chromatography coupled online with Isotopic Ratio Mass Spectrometry) and requires the use a large sample volume. Preconcentration techniques coupled to GC-IRMS systems have been successfully tested in gas analysis such as carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), and carbon monoxide (CO). In this study was tested the use of a gas preconcentration device (PreCon, Thermo Scientific), developed to determinate methane and nitrous oxide at atmospheric concentrations, in the determination of carbon isotope ratio of n-alkanes C1-C5 (methane, ethane, propane, iso-butane, n-butane, iso-pentane e n-pentane) in gas samples. The preconcentration device allows, using a few milliliters of sample, the trapping of condensable gases (C2plus, CO2, Ar, N2, O2, N2O, H2O) at low temperature (in liquid N2), while methane is oxidized, cryo-focused (as CO2) and injected in the GC-IRMS system coupled. However the equipment does not oxidize selectively the introduced compounds, it is necessary to carry out the combustion outside of preconcentrator after a chromatographic separation. This limiting represented the biggest challenge in the development of analytical methodology. The preconcentration and release of analytes were tested by evaluation of diluted standards (in PreCon) and concentrated standards in GC-IRMS system. Initially, the analyses of C1-C5 at high concentration was adjusted in the GC-IRMS system (analytical precision less than 0.2 per cent) and later was verified no fractionation due to PreCon device (analytical precision less than 0.5 per cent). The release and determination of C2plus were made by oxidation in the GC-IRMS system and was confirmed a presence of some interference in the analyses of n-butane. To ensure the selective oxidation of C1, there were tested a few modifications in the cryogenic traps and in the analytical method. The introduction of PLOT column in the traps, and the use of others cryogenic temperatures allowed to verify the quantitative collection of gas, the separation of non methane hydrocarbons and the decrease of interferences collected in liquid nitrogen (N2 and O2). Also, interferences like water, CO2, N2, O2 and olefins were minimized by introduction of a cleaning trap for the carrier gas. The developed methodology was tested analyzing the headspace of sediments that had low concentration of C2-C5 by GC-FID-TCD (Gas Chromatography with Flame ionization detector and thermal conductivity detector). Also, it was analyzed a sample of confined gas in a Isotube device. The determination of isotopic composition in these samples confirmed the applicability of methodology and system proposed. In samples with low concentration of n-alcanes, the methane was oxidized using the PreCon reator and the C2plus were concentrated using the PreCon but the oxidation was done in the GC-IRMS system. Because the reason of use two combustion reactors, the methane analysis showed high variability (more or less 2 per cent) and attempts to cryo-focus and oxidize methane in the GC-IRMS system were unsatisfactory due to co-elution. Through a PLOT column added in the preconcentration device was possible to collect the methane, however, the cryo-focusing was ineffective and the CO2 signal (product of methane oxidized) showed no identified interferences. Thus, to facilitate and ensure the simultaneous analysis of n-alcanes C1-C5, it is still necessary to install a valve to isolate the PreCon reactor allowing the direct pass of C2plus to cryo-focusing system.