title: Electrospray ionization mass spectrometry from discrete nanoliter-sized sample volumes.
abstract: We describe a method for nanoelectrospray ionization mass spectrometry (nESI-MS) of very small sample volumes. Nanoliter-sized sample droplets were taken up by suction into a nanoelectrospray needle from a silicon microchip prior to ESI. To avoid a rapid evaporation of the small sample volumes, all manipulation steps were performed under a cover of fluorocarbon liquid. Sample volumes down to 1.5 nL were successfully analyzed, and an absolute limit of detection of 105 attomole of insulin (chain B, oxidized) was obtained. The open access to the sample droplets on the silicon chip provides the possibility to add reagents to the sample droplets and perform chemical reactions under an extended period of time. This was demonstrated in an example where we performed a tryptic digestion of cytochrome C in a nanoliter-sized sample volume for 2.5 h, followed by monitoring the outcome of the reaction with nESI-MS. The technology was also utilized for tandem mass spectrometry (MS/MS) sequencing analysis of a 2 nL solution of angiotensin I.
authors.affiliation: Division of Analytical Chemistry, Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
authors.forename: Patrik
authors.initials: P
authors.lastname: Ek
authors.forename: Mårten
authors.initials: M
authors.lastname: Stjernström
authors.forename: Asa
authors.initials: A
authors.lastname: Emmer
authors.forename: Johan
authors.initials: J
authors.lastname: Roeraade
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000737:chemistry / Q000378:metabolism; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D010446:Peptide Fragments / Q000737:chemistry*; D010449:Peptide Mapping / Q000379:methods*; D040081:Protein Array Analysis; D012680:Sensitivity and Specificity; D012825:Silicon; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry; D014357:Trypsin / Q000378:metabolism
chemical_list: D007328:Insulin; D010446:Peptide Fragments; D045304:Cytochromes c; D014357:Trypsin; D012825:Silicon