Boronic acid-functionalized covalent organic polymer using Ugi reaction for the enrichment of salbutamol, ractopamine, terbutaline and ribavirin in feed.

Functionalized imine-linked covalent organic polymers (COPs) have attracted tremendous attention as adsorbent. At present, most imine-linked COPs are functionalized relying on benzene groups, limiting sufficient flexibility for grafting diverse functional groups. Herein, Ugi reaction is employed to flexibly anchor carboxylic acids and isonitriles with diverse molecular structures onto the imine bonds of COP skeletons. Considering that four illegal food additives, salbutamol, ractopamine, terbutaline and ribavirin, can specifically bind with boric acid, this work selects 4-carboxyphenylboronic acid and tert‑butyl isocyanate, yielding a boronate affinity imine-linked COP. The adsorption performance of the obtained adsorbent is investigated in detail. The as-prepared adsorbent exhibits excellent selectivity, and high adsorption capacities ranging from 119.6 to 385.3 μmol/g towards four analytes. Moreover, the developed dispersive solid-phase extraction (DSPE) combined with HPLC gives low limits of detection (0.21-0.38 μg/kg) and wide linear ranges (1.2-300.0 μg/kg) for the four targets in feed samples. These results confirm the excellent adsorption properties of the adsorbent and verify the feasibility of Ugi reaction for post-synthetic functionalization of COPs.