Development of an SPE Method Using Ionic Liquid-Based Monolithic Column for On-Line Cleanup of Human Plasma and Simultaneous Determination of Five Steroid Drugs

An 1-vinyl-3-hexyl imidazolium bromide ionic liquid-based monolithic column was prepared via in situ free radical polymerization, which was used as the sorbent of on-line solid phase extraction. The prepared material was characterized by scanning electron microscopy, nitrogen adsorption–desorption instrument and mercury intrusion porosimetry, respectively, and the results showed that the homemade monolith occupied relatively uniform porous structure and high-specific surface area of 212.53 m² g^?1. On-line solid phase extraction–high-performance liquid chromatography was performed to quantitatively analyze five steroid drugs, including betamethasone, norgestrel, halcinonide, beclomethasone dipropionate and testosterone propionate in human plasma. The determination procedure was carried out following the optimization of the mobile phase composition. Methodological validation showed that correlation coefficients of the linear regressions were in the range of 0.9989–0.9992; the values of relative standard deviation for precision were in the range of 1.39–6.15% for intra-day and 0.32–6.34% for inter-day, respectively; the values of accuracy expressed by recovery were in the range of 99.02–101.98, 93.27–102.89, 102.79–104.01, 100.04–102.61 and 100.77–102.44% for the five drugs in order, respectively; the values of relative standard deviation for repeatability calculated according to retention times and peak areas of the five drugs were in the ranges of 0.28–0.76% (n?=?5) and 0.84–2.63% (n?=?5), respectively. The results showed that the polymer monolithic column was feasible for an on-line solid phase extraction column, exhibiting good selectivity and high permeability.