The recently published quantitative TG-MS method [1] derived for the determination of oxygen containing groups on the surface of carbonaceous samples was applied and expanded for the characterization of nitrogen containing groups. The method is based on the linear relation between the amount of evolved gases and the MS peak area via proportionality constant (K) which gain the similar values for all evolved gases. These fundamentals were tested on the compounds which evolves the nitrogen groups during their thermal decomposition, concretely (NH4)2CO3 and NH4NO3. The TG-MS measurements of the studied compounds were performed under an argon atmosphere (flow rate 40 ml min-1) with heating rate 10°C min-1. The monitored MS signals were selected according to the expected gaseous products evolved during the thermal decomposition of the individual compound. The results for (NH4)2CO3 confirmed validity of this method. The values of the K for the evolved gases gain similar values (3.78×107 for H2O, 4.24×107 for NH3 and 3.82×107 for CO2) and it confirmed the suitableness of the TG-MS method also for the nitrogen containing groups. During the thermal decomposition of this compound, the nitrogen groups are evolved as ammonia and the overall decomposition process is quite simple, which results in very good agreement (Table 1) between the theoretical and experimentally determined elemental composition of all evolved gases. In the case of NH4NO3, the quality of the gaseous products evolved during the decomposition differs from the theoretical expectations (decomposition only to N2O and H2O) and plenty of the other nitrogen compounds were detected. The decomposition process is more difficult and the disagreements presented in the Table 1 implies that some other decomposition products not included in the calculations has to be present. However, it can be concluded that this method seems to be valid and suitable for the determination of nitrogen species. Finally, this method will