Nitrogen speciation in crude oil and its fractions has become an important issue due to the undesirable effects of nitrogen compounds during important petroleum refining processes. In this work, a comprehensive two-dimensional gas chromatography method with a nitrogen chemiluminescence detector (GC x GC-NCD) was used for the speciation and quantification of nitrogen compounds in middle distillates. The developed method is based on an extraction of nitrogen compounds from the hydrocarbon matrix followed by their fractionation using solid phase extraction (SPE). Two fractions were collected thus minimizing misidentifications; the first one contained anilines, indoles and carbazoles and the second one contained pyridines, quinolines and acridines. An excellent agreement for total nitrogen content was found between the results obtained with the present method and those from the American Society for Testing Materials (ASTM) method. Good recoveries, repeatability and low detection limits (LOD), in a range from 10 to 20 mu g L-1, were also achieved. (C) 2012 Elsevier Ltd. All rights reserved.