This method is for determining trace impurities in high purity ethyl benzene by gas chromatography (GC). Specific impurities identified include benzene, toluene, p-xylene, m-xylene, o-xylene, cumene, n-propylbenzene, 1,2-diethylbenzene, 1,3-diethylbenzene, and 1,4-diethylbenzene. Non-aromatics and unidentified C₉+ aromatics are determined as composites. Benzene and toluene may not be separated from the non-aromatic impurities by this method but, if required, may be determined individually by UOP Method 543, “,Trace Non-Aromatic Hydrocarbons in High-Purity Aromatics by Gas Chromatography.”, The lower limit of detection for any single component is 2 mg/kg (massppm) except for p-xylene, which has a lower detection limit of 10 mg/kg.