The tremendous amounts of terephthalic acid (TPA) produced globally require consistent monitoring of its contaminants during the different stages of production for quality control purposes. In this paper, a simple, robust and green liquid chromatography method has been developed using an isocratic 100% aqueous mobile phase at pH 2 (dilute sulfuric acid) to separate TPA contaminants (mono-, di-, and tri-carboxylic aromatic acids) on a C18 stationary phase coated with Tween 20 (polyoxyethylene(20)sorbitan monolaurate). After optimization of all chromatographic conditions, near baseline separation of the nine carboxylic acids under investigation was achieved with a 2.5 mL/min flow rate on a 5 micron C18 silica column (100 x 4.6 mm) in under 20 min. The modified stationary phase showed an excellent capability to separate structural isomers in a reasonable time, markedly better that the bare C18 stationary phase. Plots of ln retention factor versus 1/temperature showed the expected linear relationship for the di- and tri-carboxylic aromatic acids (single retention mechanism likely) but a quadratic fit for the mono-carboxylic aromatic acids (dual retention mechanism likely). Due to the stability of the surfactant modified stationary phase, future potential mass spectrometry compatibility was shown through the alternative use of trifluoroacetic acid in the 100% H2O (no Tween) mobile phase but still with UV detection. The developed method with 0.001% (vol/vol) Tween in the mobile phase was successfully used to analyze two different types of TPA industrial samples for all nine components plus revealing some other impurity peaks. The lowest limit of detection was 0.010 nmoles for o-phthalic acid and p-toluic acid (PTA), while the highest was 0.065 nmoles for 4-carboxybenzaldehyde (CBA). The concentrations of these important contaminants, PTA and CBA, in the mother liquor sample were 3348 mg/L and 1806 mg/L, respectively, while their respective concentrations in the purified TPA powder were 135 mg/kg and 17.7 mg/kg.

中文翻译：

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使用涂有吐温 20 的 C18 色谱柱对对苯二甲酸污染物进行胶束和亚胶束液相色谱分析

全球生产的大量对苯二甲酸 (TPA) 需要在生产的不同阶段对其污染物进行一致监测，以实现质量控制。在本文中，开发了一种使用等度 100% 水性流动相在 pH 2（稀硫酸）下分离 TPA 污染物（单、二和三羧酸芳香酸）的简单、稳健和绿色的液相色谱方法在涂有吐温 20（聚氧乙烯 (20) 脱水山梨糖醇单月桂酸酯）的 C18 固定相上。优化所有色谱条件后，在 5 微米 C18 硅胶柱 (100 x 4.6 mm) 上以 2.5 mL/min 的流速在 20 分钟内实现了所研究的九种羧酸的接近基线分离。改性固定相在合理的时间内显示出优异的结构异构体分离能力，明显优于裸 C18 固定相。ln 保留因子与 1/温度的关系图显示了二元和三元羧酸芳香酸的预期线性关系（可能是单一的保留机制），但对于单羧酸芳香酸（可能是双重保留机制）呈二次拟合。由于表面活性剂改性固定相的稳定性，通过在 100% H2O（无吐温）流动相中替代使用三氟乙酸，但仍具有 UV 检测功能，显示了未来潜在的质谱兼容性。开发方法为 0。流动相中的 001% (vol/vol) Tween 成功用于分析两种不同类型的 TPA 工业样品的所有九种成分，并揭示了一些其他杂质峰。邻苯二甲酸和对甲苯甲酸 (PTA) 的最低检测限为 0.010 nmole，而 4-羧基苯甲醛 (CBA) 的最高检测限为 0.065 nmole。这些重要污染物 PTA 和 CBA 在母液样品中的浓度分别为 3348 mg/L 和 1806 mg/L，而它们在纯化的 TPA 粉末中的浓度分别为 135 mg/kg 和 17.7 mg/kg。