The realization of a lab-on-a-chip system in which chemical reactions are carried out in a continuous flow mode and monitored on-line by a suitable analytical technique is the main topic of this thesis. Two types of a lab-on-a-chip were realized, both using mass spectrometry (MS) as the on-line detection technique, viz. electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) MS