Preparation And Evaluation Of Silica-particle-supported C18 Chain-containing Polymeric Monolithic Column With Large Internal Diameter For Solid Phase Extraction

The present paper presents a silica-particle-supported C18 chain-containing polymeric monolithic column with large internal diameter(shortened as supported C18 column).The supported C18 column was prepared by in-situ polymerization of stearyl methacrylate(C18,functional monomer),ethylene dimethacrylate(cross-linker),azobisisobutyronitrile(initiator)at the presence of a binary porogenic solvent consisting of methanol and cyclohexanol in a 530 ?m i.d.fused silica capillary pre-packed with 5 ?m ODS silica particles.Firstly,the preparation conditions for the supported C18 column were selected through experiments based on scanning electron microscope images and backpressure-vs-flowrate curves.The selected conditions were as follow:total monomer concentration,22.5%;volumetric ratio of methanol to cyclohexanol,V??:V???=6:4;polymerization time,5 h;polymerization temperature,60?.Then,the supported C18 column was evaluated in terms of mechanical stability and solid phase extraction performance by comparing with ODS packed column.The results demonstrated that the supported C18 column and the ODS packed column were equivalent to each other in the mechanical stability and swelling resistance to organic solvents,and the former was much better than the ODS packed column in column capacity and enrichment ratio,being about 3 times higher for the test analyte of melatonin.Finally,the supported C18 column was applied to determine melatonin in grains on a homemade on-line coupling system of solid phase extraction-high performance liquid chromatography-ultraviolet detection.The extraction and separation conditions were selected by experiments.The results obtained under the selected conditions were as follow.The recoveries of melatonin at three different concentration levels were from 91.2% to 101.8% and from 95.9% to 102.8%,and the intra-day precisions(RSD%,n=3)were in the ranges of 2.1-3.1% and 2.1-2.6%;and the detection limits were 1.0 ng/mL and 1.2 ng/m L(S/N=3)for melatonin in the rice extract and red rice extract,respectively.