Individual Abstract Info - Session: Instrumentation: New Concepts
Online Coupling of Electrocapture Using a Multiple Membrane Section Electrospray Membrane Probe Interfaced to Time-of-Flight Mass Spectrometry
Thomas P. White; Craig M. Whitehouse
Analytica of Branford, Inc., Branford, CT
Utilizing two section Electrospray membrane probes to conduct Electrocapture and release of peptide samples online with Electrospray ionization MS.
A new Electrocapture device has been used to capture and sequentially release ions in moving flow streams coupled to Electrospray mass spectrometry ES/MS. A two membrane section Electrospray membrane probe was configured to interface Electrocapture processes online with Electrospray Ionization. The stagnant electrolyte solution containing reservoirs used in Electrocapture devices previously reported have been replaced by flow through second solution channels. Second solution composition can be varied during operation using step functions or gradients of electrolyte and solvent concentration. This capability provides independent control to optimize Electrocapture and Electrospray performance simultaneously. Preconcentation, sample cleaning, reagent reactions and component separation can be performed on sample ions trapped in open tubes without solid support in Electrocapture operation online with Electrospray MS.
Electrospray ionization experiments were performed on an Analytica of Branford Corsair™ API-TOF mass spectrometer, equipped with an off axis electrospray probe. The device used in these studies was fabricated with three flowing solution channels. The first channel was the main sample solution flow channel that was separated from upstream and downstream electrodes with two independent Nafion proton exchange membranes. Voltage was applied to the upstream second solution electrode while the downstream second solution electrode was maintained near ground. Fused silica was extended from the membrane assembly through the pneumatic nebulization Electrospray probe where sample solution was Electrosprayed directly off the fused silica tubing exit tip. Electrospray total current was controlled by varying the electrolyte concentration in the downstream second solution.
Two semipermeable membrane sections each with flow through second solution channels was configured and integrated into an Electrospray inlet probe with pneumatic nebulization assist. The upstream membrane section second solution electrode was operated at or near ground potential to avoid redox reactions on upstream ground potential conductive surfaces in the sample solution flow path. An electric field was established along the sample solution flow channel connecting the first and second membrane sections to effect Electrocapture of analyte ions by applying a positive or negative electrical potential to the downstream second solution electrode. Negative polarity voltage was applied to the downsteam electrode to Electrocapture negative polarity ions in the sample solution flow channel. To Electrocapture positive polarity ions, positive polarity voltage was applied to the same Electrode. For example, leucine enkephaline was preconcentrated online with Electrospray ionization using the two membrane section assembly. In this experiment 792 nM Leucine Enkephalin in a 1:1 Methanol:Water 0.02% Acetic Acid solution was directly infused at a flow rate of 500 nl/min. while conducting negative ion polarity Electrospray ionization. When a voltage of 400 V/cm was applied to preconcentrate the Leucine Enkephalin using Electrocapture, a 4X reduction in signal was observed during the two minute preconcentration Electrocapture period. After two minutes, the voltage applied to the downstream second solution electrode was changed to release ions from the Electrocapture region. The signal of Leucine Enkephalin then increased by a factor of 2.9X from the original signal intensity observed prior to the Electrocapture preconcentration step. Online separation of mixtures of Electrocaptured sample components is achieved by a fine stepwise reduction of trapping voltage applied to the downstream second solution electrode. Methods demonstrating preconcentration of injected peptide samples using Electrocapture with salts removed followed by component separation online with Electrospray ionization will be described.Presentation Poster