BCEIA Conference 2007 - Individual Abstract Info - Session: Mass Spectrometry
Online Coupling of Electrocapture using a Multiple Membrane Section Electrospray Membrane Probe Interfaced to Time-of-Flight Mass Spectrometry
Shida Shen¹; Thomas P. White¹, Craig M. Whitehouse¹ and Juan Astorga Wells²
¹Analytica of Branford, Inc., Branford, CT 06405 USA
²Biomotif AB, Stockholm, Sweden
Multiple configurations of a new Electrocapture device have been interfaced to an Electrospray ion source Time-Of-Flight mass spectrometer. Electrocapture allows the capture and release of analyte species in open sample solution flow channels¹·². Ions moving in a sample solution flow are Electrocaptured by applying an electric field in the opposite direction to the fluid flow. The electric field is maintained in the sample solution flow through upstream and downstream semipermeable membrane sections. The two semipermeable membranes separate the sample solution from two separate second solutions in contact with upstream and downstream electrodes. The Electrocapture of sample species in solution are affected by adjusting the sample solution flow rate, the relative voltages applied to the upstream and downstream electrodes, the second solution electrolyte species and concentration and the sample solution composition. Two types of Electrocapture devices have been used in this study. The first Electrocapture device type is configured with static second electrolyte solution reservoirs that have no second solution flow. The second Electrocapture device is configured with one sample solution flow channel and two second solution flow channels as diagrammed in Figure 1. The dual membrane section Electrocapture devices were designed to accommodate round and flat semipermeable membrane geometries. Figure 1 shows an Electrocapture device configured with two flat membrane sections interfaced on line to an Electrospray ion source operating with pneumatic nebulization assist.
Second solution composition can be changed in the downstream membrane section during operation by running step functions or gradients of electrolyte concentration. The downstream membrane section serves the dual function of providing the electric field in the Electrocapture region of the sample solution flow path and supplying the total Electrospray ion current. The ability to adjust the electrolyte composition during operation allows the simultaneous optimization of the Electrocapture and Electrospray processes. Dual membrane section Electrocapture devices used in this study were interfaced to an Analytica of Branford, Inc. Corsair® Time-Of-Flight Mass Spectrometer equipped with an off axis Electrospray inlet probe including pneumatic nebulization assist and dielectric capillary inlet orifices into vacuum. The downstream second solution electrode was operated at ground potential to avoid the occurrence of oxidation or reduction (redox) reactions on conductive surfaces in contact with the sample solution. Electrical current flowing through all electrodes was monitored in the Electrocapture with Electrospray studies conducted. Fused silica tubing extended continuously from the Electrospray tip into the Electrocapture device. The Electrospray total ion current was adjusted by changing the electrolyte concentration in the downstream second solution flow channel for a given sample solution composition. The voltage applied to the upstream second solution electrode was adjusted to optimize the Electrocapture performance for a given sample solution. The dielectric capillary entrance electrode voltage was independently adjusted to optimize Electrospray performance. The dual membrane section Electrocapture devices were redesigned for this study to allow conducting Electrocapture at higher flow rates through the sample solution flow path. Higher Electrocapture flow rate allows faster sample trapping and release times and the ability to run Electrospray with pneumatic nebulization assist. Due to the dielectric capillary orifice into vacuum, the polarity of the Electrospray ions could be set to the same or opposite polarity of the Electrocaptured ions in solution.
In this study, different classes of samples were Electrocaptured as negative ions in solution and when released Electrosprayed as either positive or negative polarity ions depending on the polarity produced the highest signal response. Preconcentation, sample cleaning, reagent reactions and component separation were performed on sample ions trapped in the Electrocapture region of an open sample solution flow channel without solid support in Electrocapture operation online with Electrospray MS. Preconcentration of negative polarity peptide ions was performed by Electrocapture in the sample solution flow path. The sample solution composition and pH, flow rate and applied voltages were adjusted to optimize Electrocapture performance while minimizing reduction of Electropsray MS performance. The increase in concentration with Electrocapture based on the Electrospray MS signal was compared to sample injection without Electrocapture. The preconcentration provided an increase in signal to noise and lowered detection limits particularly in samples with interfering chemical noise peaks. Experiments were conducted in which salts and detergents were washed off Electrocaptured peptides prior to release into the Electrospray ion source. Mixtures of peptides Electrocaptured online were separated by selective release of individual peptides by adjusting the applied Electrocapture voltage and/or the downstream second solution electrolyte composition. Methods used to effect the optimization of Electrocapture performance on line with Electrospray ionization mass spectrometry will be described and results using different classes of compounds, sample solution compositions and second solution compositions will be presented.
Astorga-Wells, J. and Swerdlow H. (2003) Fluidic Preconcentrator Device for Capillary Electrophesis of Proteins. Anal. Chem., 75, 5207-5212.
Astorga-Wells, J., Jörnvall, H. And Berfman, T. (2003) A Microfluidic Electrocapture Device in Sample Prepartion of Protein Analysis by MALDI Mass Spectrometery. Anal. Chem. 75, 5213-5219.