Anal. Chem. 2009, 81, 6558–6561
Correspondence Analysis of Samples Stored as Individual Plugs in a Capillary by Electrospray Ionization Mass Spectrometry Jian Pei,† Qiang Li,† Mike S. Lee,‡ Gary A. Valaskovic,§ and Robert T. Kennedy*,†,| Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, Michigan 48109-1055, Milestone Development Services, Milestone Development Services Inc., Newtown, Pennsylvania 18940, and New Objective, Inc., 2 Constitution Way, Woburn, Massachusetts 02139 Droplets or plugs within multiphase microfluidic systems have rapidly gained interest as a way to manipulate samples and chemical reactions on the femtoliter to microliter scale. Chemical analysis of the plugs remains a challenge. We have discovered that nanoliter plugs of sample separated by air or oil can be analyzed by electrospray ionization mass spectrometry when pumped directly into a fused silica nanospray emitter tip. Using leucine-enkephalin in methanol and 1% acetic acid in water (50:50 v:v) as a model sample, we found carry-over between plugs was
