This method is for determining nitrogen in liquid hydrocarbons at concentrations ranging from 30 to 600 ng/g (mass-ppb). It is applicable to highly volatile samples, such as pentane, through the use of a cooled sampling system. Higher concentrations can be determined by ASTM Methods D4629, “Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection,” D6069, “Trace Nitrogen in Aromatic Hydrocarbons by Oxidative Combustion and Reduced Pressure Chemiluminescence Detection,” and D7184, “Ultra Low Nitrogen in Aromatic Hydrocarbons by Oxidative Combustion and Reduced Pressure Chemiluminescence Detection,” using the cooled sampling system described herein for highly volatile matrices. Halogens and sulfur interfere at concentrations greater than approximately 1%.