Development of a new in-line coupling of a miniaturized boronate affinity monolithic column with reversed-phase silica monolithic capillary column for analysis of cis-diol-containing nucleoside compounds.

In-line coupling of capillary columns is an effective means for achieving miniaturized and automated separation methods. The use of multimodal column designed to allow the direct integration of a sample preparation step to the separation column is one example. Herein we propose a novel in-line coupling at the capillary scale between a boronate affinity capillary column (μBAMC unit) and a reversed-phase separation column. This has been made possible due to the elaboration of a new and efficient μBAMC unit. A thiol-activated silica monolithic capillary column was functionalized through thiol-ene photoclick reaction. This simple and fast reaction allows to prepare stable μBAMC units having grafting densities of 1.93 ± 0.17 nmol cm-1. This grafting strategy increases the surface density by a factor 4 compared to our previous strategies and opens the frame to in-line coupling with reversed-phase capillary column. Proof of concept of the in-line coupling was done by coupling a 1-cm length μBAMC unit to a 7-cm length reversed phase capillary column. The conditions of loading, elution and separation were optimized for cis-diol nucleosides analysis (uridine, cytidine, adenosine, guanosine). A loading volume (at pH 8.5) of up to 21 hold volume (i.e 1 μl) of the μBAMC unit can be loaded without sample breakthrough. For the least retained nucleoside (uridine) a limit of detection of 50 ng mL-1 was estimated. Elution and full separation of the four nucleosides was triggered by flushing the multimodal column with an acetic acid (50 mM) / methanol (98/2, v/v) mobile phase.