Sample pretreatment processes such as concentration or classification are essential to finding trace substances present in a fluid. In scientific communities recently, prolific research is being conducted on sample pretreatment techniques utilizing electrokinetics. However, due to the lack of commercial anion-permselective material—an essential component—its potential application is limited to only negatively charged particles. To this, a research team at POSTECH has found a way to isolate and concentrate only the cationic samples.