Preparation and evaluation of a porous monolithic capillary column for microextraction of estrogens from urine and milk samples online coupled to high-performance liquid chromatography

A porous monolithic capillary column based on poly (methacrylic acid-co-ethylene glycol dimethacrylate) (poly (MAA-co-EGDMA)) was prepared using methanol and polyethylene glycol 6000 as mixed porogens. The monolith has the characteristics of good permeability, high extraction efficiency and long lifetime. Improved permeability of the monolith could realize sample loading with high flow rate. A simple and convenient construction that employed valve-switch technique was designed for online coupling of the monolithic capillary column to high performance liquid chromatography. In order to obtain optimum extraction efficiency, the extraction conditions including sample pH, sample volume, extraction and desorption flow rate were investigated. Under the optimum conditions, the enrichment factors were 180–362 for five estrogens, indicating remarkable preconcentration ability of the monolithic capillary column. The dynamic binding capacity (DBC) was estimated to be 3.73 mg mL−1 via frontal analysis. Finally the monolithic capillary column was successfully applied to online enrichment of estrogens from urine and milk samples followed by high performance chromatography. Low detection limits (S/N = 3) of the proposed method were achieved in the range of 0.04–0.35 μg L−1. The recoveries were 95.6–106.1% and 76.5–116.8% for the spiked urine and milk samples respectively, with the RSDs of 1.7–9.9%.