Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are high nutritional components. Evidence for unique effects of them is increasing. Further understanding of their independent biological functions urgently needs more efficient separation techniques. Nowadays, most of the commercially available fish oil products are the mixture of eicosapentaenoic acid ethyl ester (EPAEE) and docosahexaenoic acid ethyl ester (DHAEE). It will be convenient to directly separate esterified EPA and DHA without saponification pretreatment. However, it is of great challenge to separate EPAEE and DHAEE because of their extremely fat-soluble nature and the equivalent chain length rule. In this research, the suitability of green guanidinium ionic liquid (IL) in countercurrent chromatography (CCC) solvent system for the separation of them was evaluated for the first time. Compared with imidazolium IL and phosphonium IL, guanidinium IL based non-aqueous biphasic system showed more outstanding separation performance. The separation mechanism was elucidated in depth through quantum mechanical calculations. It was found that guanidinium IL acted a crucial role in the CCC separation, which resulted in difference of partition behavior of EPAEE and DHAEE via different hydrogen-bonding affinity. EPAEE and DHAEE were successfully separated by solvent system (n-heptane/methanol/propylguanidinium chloride ([C3Gun]Cl, 1:1:5%, v/v/m)) with high purity (>95%) in one step, which was not achieved beforehand. Moreover, an easy recycling procedure of IL had also been devised, which significantly reduced waste generated. It opens up a new way for reasonable design water-free two-phase solvent system for efficient separation of very non-polar lipid compounds.

中文翻译：

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基于胍盐离子液体的双相系统：通过逆流色谱法分离二十碳五烯酸乙酯和二十二碳六烯酸乙酯。

二十碳五烯酸（EPA）和二十二碳六烯酸（DHA）是高营养成分。它们的独特作用的证据正在增加。进一步了解它们的独立生物学功能迫切需要更有效的分离技术。如今，大多数市售鱼油产品是二十碳五烯酸乙酯（EPAEE）和二十二碳六烯酸乙酯（DHAEE）的混合物。直接分离酯化的EPA和DHA而不进行皂化预处理将很方便。但是，由于EPAEE和DHAEE具有极高的脂溶性和等效的链长规律，因此将其分离是一个巨大的挑战。在这项研究中 首次评估了绿色胍离子液体（IL）在逆流色谱（CCC）溶剂系统中对它们的分离的适用性。与咪唑类和and类相比，基于胍类的非水两相体系表现出更加出色的分离性能。通过量子力学计算深入阐明了分离机理。研究发现，胍盐IL在CCC分离中起关键作用，通过不同的氢键亲合力导致EPAEE和DHAEE的分配行为不同。第一步，用高纯度（> 95％）的溶剂系统（正庚烷/甲醇/丙基胍氯化物（[C3Gun] Cl，1：1：5％，v / v / m））成功分离EPAEE和DHAEE，这是事先没有实现的。此外，还设计了一种简便的IL回收程序，可显着减少产生的废物。它为合理设计无水两相溶剂系统开辟了一条新途径，可有效分离非极性脂质化合物。