Magnetic-covalent organic polymer solid-phase extraction coupled with high-performance liquid chromatography for the...

Magnetic solid-phase extraction is a powerful sample preparation tool. Combined with covalent organic polymers, this technique permits an excellent extraction performance. We present a sensitive, efficient, and easy operating magnetic- covalent organic polymer solid-phase extraction method. By using the magnetic covalent organic polymer nanoparticles yielded by a one-pot reaction, five fluorescent whitening agents were successfully preconcentrated and separated. The saturated extraction amounts of the magnetic covalent organic polymer nanoparticles for the five fluorescent whitening agents were in the range of 97-155 nmol/mg. Coupled with high-performance liquid chromatography, the limit of detection of the fluorescent whitening agent was improved by at least an order of magnitude compared to current literature records. Under the optimal conditions, the linear ranges of these five fluorescent whitening agents were up to 0.5-100 ng/L, the limit of detection was as low as 0.1 ng/L, and the recoveries were in the range of 78.2-105% with relative standard deviations lower than 5.5%. Meanwhile, a trace level of 7-diethylamino-4-methylcoumarin was found in a typical cosmetic sample by using this magnetic-covalent organic polymer solid-phase extraction method when coupling with high-performance liquid chromatography. Moreover, this sensitive, efficient, and easy operating sample preparation method can be extended to analysis of other analytes that have a π-π conjugated structure.