This standard describes methods for the determination of trace impurities of monocyclic aromatics in toluene, mixed Xylene and p-Xylene by Gas chromatography, CG and external calibrating. It is suitable for the determination of residual hydrocarbon impurities in chemical intermediates and solvents, especially alkanes and aromatics containing 1 to 10 carbon atoms. The detection limit of this method is 0.001 weight% and specifies precautions for purity calculation. The standard provides a scientific basis for ensuring the mass of high-purity chemicals.