The present invention provides a preanalysis treatment method for nitropolycyclic aromatic hydrocarbons present in diesel engine exhaust particulates and the like. The method comprises feeding a test solution 160 in which a sample containing polycyclic aromatic hydrocarbons is dissolved in a solvent to a silica gel column 170 using an eluent lowest in polarity among a plurality of eluents 110, 120 and 130 to be a mobile phase for the test solution unlike the solvent and to differ in polarity from each other; and then allowing polar solvents to flow in ascending order of polarity to fractionate nitropolycyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons other than the nitropolycyclic aromatic hydrocarbons.