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The evidence for unique effects of eicosapentaenoic acid and docosahexaenoic acid is growing. Further understanding and exploration of their independent effects in the nutraceutical and pharmaceutical industry is calling for the more efficient separation techniques to overcome the equivalent chain length rule of fatty acids. In this study, free eicosapentaenoic and docosahexaenoic acid were successfully separated by pH-zone-refining countercurrent chromatography for the first time. The different solvent systems and the influence of retainer and eluter concentration on the separation efficiency were investigated. A two-phase solvent system composed of nheptane/methanol/water (100:55:45, v/v) was selected with 50 mM of trifluoroacetic acid as retainer in the organic phase and 40 mM of ammonium hydroxide as an eluter in the aqueous phase for the separation of 500 mg of free fatty acids from a refined fish oil sample. 79.6 mg of eicosapentaenoic acid and 328.3 mg docosahexaenoic acid were obtained with the purities of 95.5 and 96.9% respectively determined by gas chromatography with mass spectrometry after methyl esterification. The scale-up separation of 1 g of samples from both refined and crude fish oil after urea complexation were also achieved successfully with a markedly increased concentration 150 mM of retainer, producing satisfactory yields and purities of targets.

Methanol is extremely toxic to humans if ingested or if vapors are inhaled. Facile and reliable detection of methanol is an efficient way to reduce the risk of methanol poisoning. A great challenge in methanol detection lies in distinguishing methanol under high ethanol background. In this work, a nanofilm‐based fluorescent sensor for direct distinguishing methanol from pure ethanol or liquor is presented, where no sample pretreatment or sensor array is needed. The flexible, uniform, and amorphous nanofilm is synthesized via dynamic covalent binding‐driven self‐assembly of BTN and CB‐CHO at air/DMSO interface. The nanofilm shows a large Stokes shift (≈175 nm) and excellent photostability. Different from sensing films based on drip‐permeance or drop cast of organic fluorophores, sensing performance of the nanofilm shows little dependence on substrate. With the film, an optical sensor for methanol vapor detection is built and it can distinguish methanol not only from the mixture of methanol and ethanol (with ethanol content up to 90%), but also from the liquor (45% vol). The sensor shows excellent reusability and high selectivity over many commonly used organic solvent vapors. Moreover, the sensor can be used to discriminate industrial alcohol from medical alcohol and detect methanol gas leak.