The obtained packing (microcolumn) was rinsed with methanol with intermittent (4–5 s) application of pumping pressure (~ 2 bars) to improve the compactness of the packing. The packings were conditioned with 10 min washing with methanol and 5 min with the mobile phase before the chromatographic separation/preconcentration. A schematic depiction of the packing preparation procedure and the picture of the obtained microchip are given in Fig. 1a,b.