Low-picomolar analysis of peptides by on-line coupling of fritless solid-phase extraction to sheathless capillary electrophoresis-mass spectrometry.
A novel fritless solid-phase extraction (SPE) microcartridge was designed for combination with sheathless capillary electrophoresis-mass spectrometry (sheathless CE-MS) employing a prototype porous-tip capillary for nanoelectrospray ionization (nanoESI). The inlet of the separation capillary (30μm inner diameter (id), 150μm outer diameter (od)) was inserted in a 4mm long SPE microcartridge (150μm id, 365μm od) packed with a C18 sorbent of 55-105μm particle size. Performance of the SPE-CE-MS system was evaluated using diluted solutions of the three opioid peptides dynorphin A (1-7) (DynA), endomorphin 1 (End1) and met-enkephalin (Met). Sample volumes of 1.5μL were loaded on the SPE microcartridge and the retained peptides were eluted with 22nL of an acidic methanol/water (60:40, v/v) solution. Using a pressure of 50mbar during separation to speed up the analysis, good peptide resolution was obtained with acceptable plate numbers (between 53,000 and 92,000). Intraday relative standard deviations (% RSD) for peptide migration times and peak areas were below 4% and 9%, respectively. The SPE-CE-MS method showed good linearity in the 0.05-5ngmL(-1) range and limits of detection (LODs) were 10pgmL(-1). However, loading a larger volume of sample (8μL), LODs could be decreased down to 2pgmL(-1) (2.2-3.5pM). This represents an improvement of up to 5000-fold with respect to the LODs achieved by sheathless CE-MS without on-line preconcentration demonstrating the potential of on-line SPE for further enhancing sensitivity.
Department of Analytical Chemistry, University of Barcelona, Diagonal 645, 08028 Barcelona, Spain; Biomolecular Analysis, Utrecht University, P.O. Box 80082, 3508 TB Utrecht, The Netherlands.
Silvia
S
Medina-Casanellas
Biomolecular Analysis, Utrecht University, P.O. Box 80082, 3508 TB Utrecht, The Netherlands.
Elena
E
Domínguez-Vega
Department of Analytical Chemistry, University of Barcelona, Diagonal 645, 08028 Barcelona, Spain. Electronic address: fbenavente@ub.edu.
Fernando
F
Benavente
Department of Analytical Chemistry, University of Barcelona, Diagonal 645, 08028 Barcelona, Spain.
Victoria
V
Sanz-Nebot
Biomolecular Analysis, Utrecht University, P.O. Box 80082, 3508 TB Utrecht, The Netherlands; AIMMS Division of BioAnalytical Chemistry, VU University, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
Govert W
GW
Somsen
Biomolecular Analysis, Utrecht University, P.O. Box 80082, 3508 TB Utrecht, The Netherlands.
Gerhardus J
GJ
de Jong
D004399:Dynorphins / Q000032:analysis*; D019075:Electrophoresis, Capillary / Q000379:methods; D004744:Enkephalin, Methionine / Q000032:analysis*; D057230:Limit of Detection; D013058:Mass Spectrometry / Q000379:methods; D009842:Oligopeptides / Q000032:analysis*; D052616:Solid Phase Extraction / Q000295:instrumentation / Q000379:methods
D009842:Oligopeptides; C105293:endomorphin 1; D004744:Enkephalin, Methionine; D004399:Dynorphins
Capillary electrophoresis; In-line; Mass spectrometry; Neuropeptide; Preconcentration; Sheathless