we cannot directly inject a food product or polymer-containing sample into a GC without some sample preparation.The high temperature of the injection port will result in the degradation of nonvolatile constituents and create a number of false GC peaks corresponding to the volatile degradation products formed.Mostly, the constituent of interest must be isolated from food product or the polymer-containing sample to make its concentration detectable by GC or to remove the interference of other compounds.Therefor, we must generally do some type of sample preparation, component isolation, and concentration prior to GC analysis.