This method is for determining trace hydrocarbon impurities in high purity p-xylene. The lower limit of detection for any single component is 0.002 mass %. The method can also be used for determining the total purity of the p-xylene. Mixed xylene isomers and/or diethylbenzenes in other process streams should be determined using UOP Method 744, Aromatics in Hydrocarbons by Gas Chromatography.