Biomedical subjects

Vilmos Kertesz

Publications and source records attributed to Vilmos Kertesz.

9 recordsLinked to original sources

PubMed2006

Automated sampling and imaging of analytes separated on thin-layer chromatography plates using desorption electrospray ionization mass spectrometry.

Modest modifications to the atmospheric sampling capillary of a commercial electrospray mass spectrometer and upgrades to an in-house-developed surface positioning control software package (HandsFree TLC/MS) were used to enable the automated sampling and imaging of analytes on and within large area surface substrates using desorption electrospray ionization mass spectrometry. Sampling and imaging of rhodamine dyes separated on TLC plates were used to illustrate some of the practical applications of this system. Examples are shown for user-defined spot sampling from separated bands on a TLC plate (one or multiple spots), scanning of a complete development lane (one or multiple lanes), or imaging of analyte bands in a development lane (i.e., multiple lane scans with close spacing). The post data acquisition processing and data display aspects of the software system are also discussed.

Chromatography, Thin Layer↗

PubMed2006

Expanded use of a battery-powered two-electrode emitter cell for electrospray mass spectrometry.

A battery-powered, controlled-current, two-electrode electrochemical cell containing a porous flow-through working electrode with high surface area and multiple auxiliary electrodes with small total surface area was incorporated into the electrospray emitter circuit to control the electrochemical reactions of analytes in the electrospray emitter. This cell system provided the ability to control the extent of analyte oxidation in positive ion mode in the electrospray emitter by simply setting the magnitude and polarity of the current at the working electrode. In addition, this cell provided the ability to effectively reduce analytes in positive ion mode and oxidize analytes in negative ion mode. The small size, economics, and ease of use of such a battery-powered controlled-current emitter cell was demonstrated by powering a single resistor and switch circuit with a small-size, 3 V watch battery, all of which might be incorporated on the emitter cell.

Journal Article↗

PubMed2005

Expanded electrochemical capabilities of the electrospray ion source using porous flow-through electrodes as the upstream ground and emitter high-voltage contact.

Use of a porous flow-through electrode at the upstream ground contact or at both the upstream ground contact and the high-voltage emitter contact in an electrospray ion source was shown to provide for new types of electrochemical experiments utilizing only the electrochemistry inherent to electrospray. The normal stainless steel bore-through union serving as the upstream grounding point in a floated electrospray emitter system was replaced with a high surface area porous flow-through electrode assembly to achieve effective electrochemical reduction of analytes at this point in positive ion mode, and effective electrochemical oxidation of analytes in negative ion mode. This was demonstrated by the oxidation of 3,4-dihydroxybenzoic acid and reserpine in negative ion mode and by the reduction of thionine in positive ion mode. In the case of reversible oxidation (3,4-dihydroxybenzoic acid) and reduction (thionine) processes, partial rereduction and reoxidation of the products due to reaction with products generated by cathodic and anodic processes at the emitter were observed, respectively. By implementing two high surface area porous flow-through electrodes in the system, one as the upstream grounding point and the other as the emitter electrode, a multiple-step reaction scheme was achieved that included consecutive electrochemical reduction and oxidation reactions and a following chemical reaction as demonstrated by the hydroquinone tagging of an initially disulfide-linked peptide.

Electrochemistry↗

PubMed2005

Automation of a surface sampling probe/electrospray mass spectrometry system.

An image analysis automation concept and the associated software (HandsFree TLC/MS) were developed to control the surface sampling probe-to-surface distance during operation of a surface sampling electrospray system. This automation system enables both "hands-free" formation of the liquid microjunction used to sample material from the surface and hands-free reoptimization of the microjunction thickness during a surface scan to achieve a fully automated surface sampling system. The image analysis concept and the practical implementation of the monitoring and automated adjustment of the sampling probe-to-surface distance (i.e., liquid microjunction thickness) are presented. The added capabilities for the preexisting surface sampling electrospray system afforded through this software control are illustrated by an example of automated scanning of multiple development lanes on a reversed-phase C8 TLC plate and by imaging inked lettering on a paper surface. The post data acquisition processing and data display aspects of the software package are also discussed.

Chromatography, Thin Layer↗

PubMed2005

Study and application of a controlled-potential electrochemistry-electrospray emitter for electrospray mass spectrometry.

This paper discusses continued studies and new analytical applications of a recently developed three-electrode controlled-potential electrochemical cell incorporated into an electrospray ion source (Van Berkel, G. J.; Asano, K. G.; Granger, M. C. Anal. Chem. 2004, 76, 1493-1499.). This cell contains a porous flow-through working electrode (i.e., the emitter electrode) with high surface area and auxiliary electrodes with small total surface area that are incorporated into the emitter electrode circuit to control the electrochemical reactions of analytes in the electrospray emitter. The current at the working and auxiliary electrodes, and current at the grounding points upstream and downstream of the emitter in the electrospray circuit, were recorded in this study, along with the respective mass spectra of model compound reserpine, under various operating conditions to better understand the electrochemical and electrospray operation of this emitter cell. In addition to the ability to control analyte oxidation in positive ion mode (or reduction in negative ion mode) in the electrospray emitter, this emitter cell system was shown to provide the ability to efficiently reduce analytes in positive ion mode and oxidize analytes in negative ion mode. This was demonstrated by the reduction of methylene blue in positive ion mode and oxidation of 3,4-dihydroxybenzoic acid in negative ion mode. Also, the ability to control electrochemical reactions via potential control was used to selectively ionize (oxidize) analytes with different standard electrochemical potentials within mixtures to different charge states to overcome overlapping molecular ion isotopic clusters. The analytical benefit of this ability was illustrated using a mixture of nickel and cobalt octaethylporphyrin.

Cobalt↗

PubMed2005

Thin-layer chromatography/electrospray ionization triple-quadrupole linear ion trap mass spectrometry system: analysis of rhodamine dyes separated on reversed-phase C8 plates.

The direct analysis of separated rhodamine dyes on reversed-phase C(8) thin-layer chromatography plates using a surface sampling/electrospray emitter probe coupled with a triple-quadrupole linear ion trap mass spectrometer is presented. This report represents continuing work to advance the performance metrics and utility of this basic surface sampling electrospray mass spectrometry system for the analysis of thin-layer chromatography plates. Experimental results examining the role of sampling probe spray end configuration on liquid aspiration rate and gas-phase ion signal generated are discussed. The detection figures-of-merit afforded by full-scan, automated product ion and selected reaction monitoring modes of operation were examined. The effect of different eluting solvents on mass spectrum signal levels with the reversed-phase C(8) plate was investigated. The combined effect of eluting solvent flow-rate and development lane surface scan rate on preservation of chromatographic resolution was also studied. Analysis of chromatographically separated red pen ink extracts from eight different pens using selected reaction monitoring demonstrated the potential of this surface sampling electrospray mass spectrometry system for targeted compound analysis with real samples.

Journal Article↗

PubMed2004

Efficient analyte oxidation in an electrospray ion source using a porous flow-through electrode emitter.

This article describes the components, operation, and use of a porous flow-through electrode emitter in an electrospray ion source. This emitter electrode geometry provided enhanced mass transport to the electrode surface to exploit the inherent electrochemistry of the electrospray process for efficient analyte oxidation at flow rates up to 800 microL/min. An upstream current loop in the electrospray source circuit, formed by a grounded contact to solution upstream of the emitter electrode, was utilized to increase the magnitude of the total current at the emitter electrode to overcome current limits to efficient oxidation. The resistance in this upstream current loop was altered to control the current and "dial-in" the extent of analyte oxidation, and thus, the abundance and nature of the oxidized analyte ions observed in the mass spectrum. The oxidation of reserpine to form a variety of products by multiple electron transfer reactions and oxidation of the ferroceneboronate derivative of pinacol to form the ES active radical cation were used to study and to illustrate the performance of this new emitter electrode design. Flow injection, continuous infusion, and on-line HPLC experiments were performed.

Borates↗

PubMed2002

Enhanced study and control of analyte oxidation in electrospray using a thin-channel, planar electrode emitter.

A thin-channel, planar electrode emitter device is described and utilized for the study and control of electrochemical oxidation of analytes at the emitter electrode in an electrospray ion source. For analytes that are not particularly susceptible to oxidation, the planar electrode device functions analytically in a manner similar to emitter systems that utilize the more common stainless steel tubular electrodes. For more easily oxidized analytes, the device provides the means to achieve near 100% oxidation efficiency or to completely eliminate analyte oxidation through simple and rapid changes in electrode material, electrode area, electrode covering, channel height above the electrode, or solution flow rate. Compared to the use of tubular electrodes, the planar electrode emitter system provides improved flexibility in altering the nature of the electrode area and material, as well as altering analyte mass transport to the electrode surface. Each of these parameters is critical in the control of electrochemical reactions and can be easily studied or exploited with this emitter electrode configuration.

Journal Article↗

PubMed2002

Surface-assisted reduction of aniline oligomers, N-phenyl-1,4-phenylenediimine and thionin in atmospheric pressure chemical ionization and atmospheric pressure photoionization.

Reduction of the oligomers formed from on-line electropolymerization of aniline, the compound N-phenyl-1,4-phenylenediimine, and the thiazine dye thionin was observed in both an atmospheric pressure chemical ionization and an atmospheric pressure photoionization source. The reduction, which alters the mass of these analytes by 2 Da, was shown to occur by means of a surface-assisted process which involves reactive species, possibly hydrogen radicals, generated from protic solvents in the ionization plasma. Reduction was minimized by limiting protic solvents, by using a high heated nebulizer temperature, and by using a clean, heated nebulizer probe liner. The expected generality of this reduction process, and the possibility of similar reduction processes in other plasma ionization sources are discussed in relation to the use of these ion sources for on-line electrochemistry/mass spectrometry experiments.

Journal Article↗