Layer-by-layer self-assembly of polyelectrolyte multilayers on silica spheres as reversed-phase/hydrophilic interaction mixed-mode stationary phases for high performance liquid chromatography.

In this study, a series of stationary phases, comprising silica spheres and polyelectrolyte multilayers (PEMs) as the core and surface coating, respectively, were prepared via a layer-by-layer self-assembly approach for use in high-performance liquid chromatography. PEMs coatings were formed by the alternate deposition of positively charged poly(allylamine hydrochloride) and negatively charged poly(ethylene-alt-maleate) anions which were synthesized by esterification between poly(ethylene-alt-maleic anhydride) and n-alkyl alcohols (CnH2n+1OH, n=4, 8, 10, 12). The chromatographic performance and retention mechanism of the new stationary phases were evaluated in simultaneous reversed-phase/hydrophilic interaction mixed-mode chromatography using different solute probes, such as alkyl benzene, p-hydroxybenzoic acid and its esters, anilines, phenols, and pyrimidines. The separation performance of the new stationary phases was optimized by tuning the n-alkyl chain length of poly(ethylene-alt-maleate) and bilayer numbers of PEMs. These results indicated that the new stationary phases demonstrate promise for the simultaneous separation of complex hydrophobic and hydrophilic samples with high selectivity.