Thesis (M.Sc.)--Chulalongkorn University, 2009

Isophthalic acid (IPA) has been used to help improve the properties of polyethylene terephthalate (PET) and in the production process precise amount of IPA to be added into PET resin must be known. However, the only known quantitative monitoring of the concentration of IPA in PET resin is the FTIR analysis which is an inhouse method and time consuming. In this research a gas chromatographic method for the quantitative analysis of IPA has been proposed. In this method the IPA was quantified by dissolving the PET resin in methanol in the presence of base catalyst in a micro-reactor and the resulting methyl ester was analyzed using diethylphthalate as an internal standard. The results indicated that the gas chromatographic method was more accurate than the FTIR method. Moreover, the analysis of IPA in PET resin was carried out within a short time.