Synthesis of silica amino-functionalized microporous organic network composites for efficient on-line solid phase extraction of trace phenols from water.

Microporous organic network (MON) is a promise class of functional materials in solid phase extraction (SPE). However, the previous MON-based SPE works are all focused on off-line mode. The inherent drawbacks of off-line SPE such as complicated operation steps and poor repeatability still hinder the potential applications of MON. In addition, direct use of traditional synthesized nano-sized MON in on-line SPE is impractical. To solve these issues, here we show the synthesis of silica amino-functionalized MON (SiO2@MON-NH2) microsphere as an advanced adsorbent for on-line SPE of trace phenols prior to the high performance liquid chromatography (HPLC) analysis. The SiO2 microsphere is served as the core to support the in-situ engineering of MON-NH2 to reduce the back pressure during on-line SPE. Integrating amino groups (hydrogen binding sites) with aromatic MON's networks (hydrophobic and π-π interaction sites) on SiO2@MON-NH2 provides supersensitive performance for phenols. The SiO2@MON-NH2 microsphere for on-line SPE coupled with HPLC for the analysis of five phenols offers low limit of detections (S/N = 3, 0.009-0.030 μg L-1), wide linear range (0.025-100 μg L-1), large enrichment factors (5036-5689) and good intra-day and inter-day precisions (RSDs, 0.7-1.6 and 1.0-2.7%, respectively). The proposed method is also successfully applied to analyze trace phenols in tap, lake and river water samples with good recoveries. The newly-synthesized MON composites own great potential in on-line SPE for further determination of diverse trace contaminants.