title: Analysis of samples stored as individual plugs in a capillary by electrospray ionization mass spectrometry.
abstract: 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 <0.1% and relative standard deviation of signal for a series of plugs was 3%. Detection limits were 1 nM. Sample analysis rates of 0.8 Hz were achieved by pumping 13 nL samples separated by 3 mm long air gaps in a 75 microm inner diameter tube. Analysis rates were limited by the scan time of the ion trap mass spectrometer. The system provides a robust, rapid, and information-rich method for chemical analysis of sample in segmented flow systems.
authors: Jian
authors: J
authors: Pei
authors: Qiang
authors: Q
authors: Li
authors: Mike S
authors: MS
authors: Lee
authors: Gary A
authors: GA
authors: Valaskovic
authors: Robert T
authors: RT
authors: Kennedy
mesh_terms: D000388:Air; D019075:Electrophoresis, Capillary; D004745:Enkephalins / Q000032:analysis* / Q000737:chemistry; D007930:Leucine / Q000032:analysis* / Q000737:chemistry; D046210:Microfluidic Analytical Techniques; D010446:Peptide Fragments / Q000032:analysis*; D012997:Solvents / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D014867:Water / Q000737:chemistry
chemical_list: D004745:Enkephalins; D010446:Peptide Fragments; D012997:Solvents; D014867:Water; D007930:Leucine