Preparation of porous polymer monolithic column incorporated with graphene nanosheets for solid phase microextraction and enrichment of glucocorticoids

Novel monolithic capillary columns with embedded graphene were developed and used for polymer monolith microextraction (PMME) coupled to LC–MS analysis. The column was prepared inside fused silica capillaries (320 μm, i.d.) using thermally initiated free-radical polymerization with butyl methacrylate (BMA) as monomer, ethylene dimethacrylate (EDMA) as cross-linker, and 1,4-butanediol and 1-propanol as porogens. Graphene (GN) was incorporated into the poly(BMA–EDMA) monolith to enhance the loading capacity. The obtained GN and the poly(BMA–EDMA–GN) monolith were characterized by transmission electron microscope (TEM), atomic force microscopic (AFM) and scanning electron microscopy (SEM). The extraction performance of the monolithic column was evaluated by glucocorticoids (GCs) as the analytes. The operation parameters of PMME including desorption solvent, sample flow rate, sample volume, sample pH, and eluent flow rate were studied and optimized. When compared to the parent poly(BMA–EDMA) column and direct sample analysis, high enrichment capacity was observed in the case of GN-entrapped monolith. The GN incorporated monolithic capillary showed satisfactory reusability and stability during extraction. The limits of detection (S/N = 3) for nine GCs were in the range of 0.13–1.93 ng/mL. Relative standard deviations for the determination of the target GCs were less than 14.5%. Finally, the PMME method, based on the developed monolithic capillary as the extraction media, was successfully applied to the determination of nine GCs in cosmetics. The recoveries of GCs spiked in different matrices ranged from 83.7% to 103.8%.