Liquid aliphatic and aromatic hydrocarbons play an important role in refining processes, in the petrochemical, chemical and polymer industry, either as raw materials, process intermediates, or as end products. Regardless of their source or their further use, they all have in common that they need to be ultra-pure. This means that they have to be free of undesired compounds, as these could affect the production process and the quality of the final products. Impurities such as nitrogen-containing compounds not only affect the performance and economic life of catalysts used in the production process (catalyst poisoning), but also form unwanted by-products and thereby decrease the quality of the end products. Therefore their content has to be kept as low as possible, preferably below 100 ppb. To make this possible, the exact knowledge of the present nitrogen (TN) is required. Combustion-based elemental analysis coupled with a pressure-reduced chemiluminescence detector is the only method that has proven to be suitable for this challenging task.