For the preparation of chromatographic packing, similar processwas
applied to the one used in our earlierworks [14]. The 12 channels of the
microchip were packed simultaneously from port E, pumping a single
plug of C18 suspension splitted toward the other ends of the parallel
channels. Briefly, a suspension (~100 μL) of freshly ultrasonicated,
methanolic C18 particles of 5 μm was manipulated through a smallbore
tubing (0.25 mm ID) using a peristaltic pump. The tubing was connected to the port E (Fig. 1a,b), and the particles were washed
with methanol (~10 μL/min) toward the frit at the end of the channels
(ports S).