Universal approach for mesofluidic handling of bead suspensions in lab-on-valve format

In the present report, new protocols are introduced for automatic mesofluidic handling of irregularly shaped and non-uniformly sized bead materials for renewable micro-solid phase extraction (mu SPE) under the lab-on-valve (LOV) format. To this end, two alternative strategies were studied comprising either (i) the direct aspiration of bead suspension placed at a container attached to LOV device or (ii) the aspiration of beads after a resuspension step, allowing the formation of a fluidized bed inside the beads' container. Suspensions with homogeneously dispersed beads were also tested in the first strategy above, as prepared by increasing the viscosity of the suspension milieu with 75:15:10 glycerol/MeOH/H2O (in wt). The bead injection protocols were applied to four commercial reversed-phase sorbent materials with different sorptive surfaces: Oasis HLB, SupelMIP beta-receptors, Lichrolut EN and Discovery DSC-MCAX, and the mass of sorbent packed in each microcolumn was assessed. Direct aspiration of methanolic suspensions gave rise to bead stacking and clogging of the LOV microconduits, resulting in a source of results with poor precision (RSD: 3.8-67.6%). The use of glycerolic suspensions was merely effective for repeatable sampling and packing of Oasis HLB and SupelMIP beta-receptor beads without sorbent settlement along time. The resuspension strategy was able to handle all the materials tested with acceptable precision (RSD: 1.6-13.8%). Enhanced precision was attained (RSD < 4.1%) when the sorbent bed was physically restricted to the volume of the LOV microchannel cavity. Different volumes of suspension aiming at a target mass of sorbent of 10 mg were successfully handled (RSD: 3.1-13.8%), showing the reliability of the bead resuspension approach for varied nominal bead sampling volumes. The proposed bead handling protocols were applied to mu SPE of propranolol taken as a model of beta-blocker from aqueous solutions by SupelMIP beta-receptors and Discovery DSC-MCAX beads with high repeatability (RSD < 6%) and absolute recoveries between 69 and 74% in a bead-injection mode. (C) 2011 Elsevier B.V. All rights reserved.