Capillary-based solid-phase extraction with columns prepared using different bead trapping methods.

Abstract

Three approaches of bead immobilization for CEC column preparation in a capillary were examined for SPE. The three approaches included a packed column with a single frit, a packed column with an inlet and outlet frit, and an entrapped column where beads were immobilized within an organic polymer. A direct comparison of SPE/preconcentration of 4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene and 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-propionic acid with a 2 cm long bed showed that the entrapped column yielded the best performance in terms of reproducibility and robustness. The room temperature chemistry utilized to form the entrapped column enables the column to be photopatterned anywhere within the capillary without loss in bead functionality, and effectively links individual beads to one another at specific bead-bead and bead-capillary contact points. A 0.5 cm long entrapped bed exhibits high mechanical strength and is able to withstand >4400 psi. The entrapped bed was used to preconcentrate progesterone and beta-estradiol providing signal enhancements of >600. Following preconcentration, the hormones could be separated using CEC. With the current availability of numerous well-characterized chromatographic packing materials and the relative simplicity of the fabrication method, this methodology can be readily adapted to HPLC, CEC, and micro total analysis system.