Capillary liquid chromatography interfaced to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using an on-line coupled piezoelectric flow-through microdispenser

A piezoelectric how-through microdispenser interfacing capillary liquid chr omatography (LC) with matrix-assisted laser desorption/ionization time-of-f ight mass spectrometry (MALDI-TOF MS) was developed for the identification of biomolecules, The MALDI target plate was placed on a computer controlled high-resolution x-y stage, on to which the column effluent was deposited a s discrete spots, which thereby facilitated tracing of the chromatographic separation. The entire target plate was sprayed with a homogeneous layer of alpha-cyano-4-cinnamic acid mixed with nitrocellulose by using an air-brus h. Hence the tedious manual handling of a micropipetter applying matrix sol ution on top of each fraction collected spot was avoided. The pre-made targ et plates were stable for at least 3 weeks if kept in darkness at room temp erature, which easily allowed re-analysis of dispensed sample spots. The in tegrated microsystem was characterized and optimized by means of fluidics, dispersion, operational stability and sensitivity parameters. The dispensin g unit was developed specifically to match high-resolution capillary LC sep arations using a dispenser with an internal volume from inlet to the ejecti ng nozzle of 250 nl, Minimizing dead volumes was crucial in order to mainta in the chromatographic resolution. The volume of the ejected droplets was o f the order of 60 pi, Successful separations of seven immunoregulating pept ides were made: ACTH 1-17, bradykinin, enkephalin, angiotensin III, angiote nsin II, angiotensin I and ACTH 18-39, On-line sample dispensing on the tar get plate in combination with trace enrichment followed by automated MALDI- TOF MS identification is demonstrated, reaching a sensitivity of 100 amol, Copyright (C) 2000 John Wiley & Sons, Ltd.