This method is for determining trace impurities in high-purity mixed xylenes by gas chromatography (GC). Specific trace impurities determined include non-aromatic hydrocarbons, benzene, toluene and individual C9 and C10 aromatic compounds. C10 or higher non-aromatics, if present, may interfere with the determination of benzene. These can be determined by UOP Method 543. The lower limit of quantitation for any single component is 1 mg/kg (mass-ppm). Impurities at concentrations above 500 mg/kg should be determined by UOP Method 744.
The sample is injected into a gas chromatograph that is equipped with an autoinjector, SSL injector, fused silica capillary column internally coated with poly(ethylene glycol), and a flame ionization detector.
The concentrations of individual or group impurities are determined by the external standard (ESTD) method of quantitation, wherein peak areas of the sample components are compared to the peak areas of a calibration blend analyzed under identical conditions and injection volumes.