This gas chromatographic method is for determining trace impurities in 99%+ purity styrene. Benzene and toluene are not separated from the non-aromatic impurities by this method but, if required, may be determined individually by UOP Method 543. Heavy non-aromatics may interfere with the determination of the C8 aromatics and cumene. This method can also be used to calculate the total purity of styrene. The lower limit of detection for an individual impurity is 2 mass-ppm. Sample composition may change with time and, therefore, samples should be protected from air and analyzed soon after receipt.