关键词: 苯二甲酸异构体, 反相液相色谱, 保留行为, 热力学参数

Abstract:

Polyethylene terephthalate (PET), commonly known as polyester, is a condensation of terephthalic acid (TPA) and ethylene glycol (EG). In the process of PET production and processing, IPA and PA are widely used as important additives. In the process of production and use, the residual or degraded phthalic acid substances will seriously harm human health if they accidentally enter the human body. At home and abroad, no matter as packaging materials for food and medicine, or as fabrics for underwear, there are corresponding national standards for the residual or migratory amount of TPA, IPA and PA. Therefore, in the process of analysis and detection, it is necessary to be able to quickly separate the three and accurately quantify them.

Reversed phase liquid chromatography (RPLC) has been widely used in chromatographic analysis because of its advantages such as small sample size, good separation and excellent repeatability. In order to further optimize the separation effect of benzoic acid isomers in liquid chromatography, we studied the chromatographic retention behavior of benzoic acid isomers in C18 stationary phase with different proportions of mobile phase and different temperatures using methanol aqueous solution as the mixed mobile phase, and calculated the thermodynamic parameters of the interaction between benzoic acid isomers and stationary phase. The stationary phase was C18 column in RPLC, and the mobile phase was 15%~45% methanol aqueous solution. It was found that the Van't Hoff curve and the lnk and Ψ had a good linear relationship in the temperature range of 10 to 50 ℃. In the process of binding with C18 column fixation, the binding mechanism did not change, and the retention behavior of terephthalic acid isomers controlled by mobile phase composition and column temperature was continuous and stable. Both ΔH0 and ΔS0 are negative values, indicating that the benzoic acid isomers are bound, the degree of freedom decreases, and energy is released during the process of C18 column fixation. Under the same methanol ratio, ΔH0 and ΔS0 values of TPA and IPA are close to and greater than PA, indicating that the binding energy of TPA and IPA with C18 column is greater than PA and decreases with the increase of methanol ratio.

The position difference of PA, TPA and IPA3 isomer dicarboxylate on the benzene ring can be obviously reflected in RPLC retention behavior. Better separation effect and accurate quantification can be obtained by adjusting the proportion of mobile phase and column temperature. The study of its retention behavior and thermodynamic properties can provide an effective method for the separation of other types of isomers, and also provide basic data for analysis tasks such as polyester degradation recovery, ecological environmental protection, and food contact material migration.

Key words: phthalic acid isomer, RPLC, retention behavior, thermodynamic parameter