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Article: Theoretical and experimental studies of electrostatic effects in reversed-phase liquid chromatography.

Weber, S G

2006 Volume 36, Issue 1-2, Page(s) 99–106

Abstract: Electrostatic effects are important in many reversed-phase liquid chromatographic separations involving surfactants and ion-pair reagents. To give better understanding of such systems the Poisson-Boltzmann equation has been solved for two cases. The ... ...

Abstract	Electrostatic effects are important in many reversed-phase liquid chromatographic separations involving surfactants and ion-pair reagents. To give better understanding of such systems the Poisson-Boltzmann equation has been solved for two cases. The first is that of an infinitely long cylinder with charge density on the inner wall, and two phases in the interior, one in the center and the other around it. Salts with ions of various solubilities in each phase may be present. The solution is obtained for the low-potential case (Deltapsie / kT 1). The second case is that of a planar sandwich, wall/phase 1/phase 2/phase 1/wall, with the same chemistry as case 1 but without the low-potential restriction. In case 2, there is also a Langmuir adsorption isotherm for each ion. The theory shows that the information gained from the Stern-Gouy-Chapman theory, which is mathematically semi-infinite, only applies when the diffuse layer thickness is much smaller than the pore radius, an unlikely circumstance in chromatography. The volume-averaged electrostatic potential difference can be measured experimentally with the solutes ø(4)Si, ø(4)As(+), ø(4)B(-) (ø = phenyl). The results are in agreement with theory. They show that the electrostatics of the system is dominated by fixed charges on the silica when the salt present is insoluble in the stationary phase, but when ions with some solubility in the stationary phase are used, mixed effects are obtained.
Language	English
Publishing date	2006-01-23
Publishing country	Netherlands
Document type	Journal Article
ZDB-ID	1500969-5
ISSN	1873-3573 ; 0039-9140
ISSN (online)	1873-3573
ISSN	0039-9140
DOI	10.1016/0039-9140(89)80084-0
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Article ; Online: Electroosmotic push-pull perfusion: description and application to qualitative analysis of the hydrolysis of exogenous galanin in organotypic hippocampal slice cultures.

Rupert, Amy E / Ou, Y / Sandberg, M / Weber, S G

ACS chemical neuroscience

2013 Volume 4, Issue 5, Page(s) 838–848

Abstract: We demonstrate here a method that perfuses a small region of an organotypic hippocampal culture with a solution containing an enzyme substrate, a neuropeptide. Perfusate containing hydrolysis products is continually collected and subsequently analyzed ... ...

Abstract	We demonstrate here a method that perfuses a small region of an organotypic hippocampal culture with a solution containing an enzyme substrate, a neuropeptide. Perfusate containing hydrolysis products is continually collected and subsequently analyzed for the products of the enzymatic degradation of the peptide substrate. The driving force for perfusion is an electric field. The fused silica capillaries used as "push" and "pull" or "source" and "collection" capillaries have a ζ-potential that is negative and greater in magnitude than the tissue's ζ-potential. Thus, depending on the magnitudes of particular dimensions, the electroosmotic flow in the capillaries augments the fluid velocity in the tissue. The flow rate is not directly measured; however, we determine it using a finite-element approach. We have determined the collection efficiency of the system using an all d-amino acid internal standard. The flow rates are low, in the nL/min range, and adjustable by controlling the current or voltage in the system. The collection efficiency of the d-amino acid peptide internal standard is variable, increasing with increased current and thus electroosmotic flow rate. The collection efficiency can be rationalized in the context of a Peclet number. Electroosmotic push-pull perfusion of the neuropeptide galanin (gal1-29) through the extracellular space of an organotypic hippocampal culture results in its hydrolysis by ectopeptidase reactions occurring in the extracellular space. The products of hydrolysis were identified by MALDI-MS. Experiments at two levels of current (8-12 μA and 19-40 μA) show that the probability of seeing hydrolysis products (apparently from aminopeptidases) is greater in the Cornu Ammonis area 3 (CA3) than in the Cornu Ammonis area 1 (CA1) in the higher current experiments. In the lower current experiments, shorter peptide products of aminopeptidases (gal13-29 to gal20-19) are seen with greater frequency in CA3 than in CA1 but there is no statistically significant difference for longer peptides (gal3-29 to gal12-29).
MeSH term(s)	Aminopeptidases ; Animals ; Electric Stimulation ; Electroosmosis/methods ; Extracellular Space/metabolism ; Galanin/metabolism ; Hippocampus/metabolism ; Hydrolysis ; Organ Culture Techniques ; Perfusion/methods ; Rats ; Rats, Sprague-Dawley ; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
Chemical Substances	Galanin (88813-36-9) ; Aminopeptidases (EC 3.4.11.-)
Language	English
Publishing date	2013-04-30
Publishing country	United States
Document type	Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't
ISSN	1948-7193
ISSN (online)	1948-7193
DOI	10.1021/cn400082d
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Article ; Online: Assessment of tissue viability following electroosmotic push-pull perfusion from organotypic hippocampal slice cultures.

Rupert, Amy E / Ou, Y / Sandberg, M / Weber, S G

ACS chemical neuroscience

2013 Volume 4, Issue 5, Page(s) 849–857

Abstract: We have developed a novel sampling technique that allows both introduction and removal of fluid from the extracellular space of living tissue. This method is based on the fluidics of push-pull perfusion but flow is driven by electroosmosis. We have ... ...

Abstract	We have developed a novel sampling technique that allows both introduction and removal of fluid from the extracellular space of living tissue. This method is based on the fluidics of push-pull perfusion but flow is driven by electroosmosis. We have applied this method to organotypic hippocampal cultures. A source capillary is inserted into the tissue and a collection capillary is in contact with the tissue surface through a thin layer of fluid. A voltage is applied across the proximal ends of source and collection capillary. In the applied field, fluid will move from source, into the tissue, and then be collected. In this process, damage to cells may occur. To understand better what sampling conditions influence damage most, we tested various sampling geometries and applied voltages, quantifying damage 16-24 h later using propidium iodide as a cell death marker. We found that damage correlates with both voltage drop and power dissipated in the tissue, but that voltage drop is a better indicator of damage when comparing models in which capillary arrangement and length are different.
MeSH term(s)	Animals ; Cell Death ; Electric Stimulation/adverse effects ; Electroosmosis ; Hippocampus/injuries ; Organ Culture Techniques ; Perfusion/adverse effects ; Rats ; Rats, Sprague-Dawley ; Tissue Survival
Language	English
Publishing date	2013-05-02
Publishing country	United States
Document type	Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't
ISSN	1948-7193
ISSN (online)	1948-7193
DOI	10.1021/cn4000814
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Article ; Online: High temporal resolution delayed analysis of clinical microdialysate streams.

Gowers, S A N / Hamaoui, K / Cunnea, P / Anastasova, S / Curto, V F / Vadgama, P / Yang, G-Z / Papalois, V / Drakakis, E M / Fotopoulou, C / Weber, S G / Boutelle, M G

The Analyst

2018 Volume 143, Issue 3, Page(s) 715–724

Abstract: This paper presents the use of tubing to store clinical microdialysis samples for delayed analysis with high temporal resolution, offering an alternative to traditional discrete offline microdialysis sampling. Samples stored in this way were found to be ... ...

Abstract	This paper presents the use of tubing to store clinical microdialysis samples for delayed analysis with high temporal resolution, offering an alternative to traditional discrete offline microdialysis sampling. Samples stored in this way were found to be stable for up to 72 days at -80 °C. Examples of how this methodology can be applied to glucose and lactate measurement in a wide range of in vivo monitoring experiments are presented. This paper presents a general model, which allows for an informed choice of tubing parameters for a given storage time and flow rate avoiding high back pressure, which would otherwise cause the microdialysis probe to leak, while maximising temporal resolution.
Language	English
Publishing date	2018-01-30
Publishing country	England
Document type	Journal Article
ZDB-ID	210747-8
ISSN	1364-5528 ; 0003-2654
ISSN (online)	1364-5528
ISSN	0003-2654
DOI	10.1039/c7an01209h
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Zs.A 2423: Show issues

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Article: Signal-to-noise ratio in microelectrode-array-based electrochemical detectors.

Weber, S G

Analytical chemistry

1989 Volume 61, Issue 4, Page(s) 295–302

Abstract: The signal-to-noise ratio at an electrode array depends on the electrode area, the perimeter-to-area ratio of the electroactive portion of the surface, the mass transfer coefficient of the analyte-electrode combination, the measurement bandwidth, and the ...

Abstract	The signal-to-noise ratio at an electrode array depends on the electrode area, the perimeter-to-area ratio of the electroactive portion of the surface, the mass transfer coefficient of the analyte-electrode combination, the measurement bandwidth, and the sources and magnitudes of the noises. Simple models for chronoamperometry with an array in quiescent solution and for hydrodynamic current at an array in one wall of a rectangular conduit through which analyte-containing solution is following are given. Noises from seven sources, including environmental noises, are considered in a noise model. The signal and noise models are combined to yield a model for signal-to-noise ratio at array-based electrochemical detectors. There exists an optimum array density for a given area that depends on the noise power, noise resistance, the current density at a sparse array, and the current density at a solid electrode of the same area. Approximations that lead to simple expressions for the optimum electroactive area fraction and noise resistance lead to results that are in good agreement with more complex and less approximate calculations. Electrodes of millimeter dimensions consisting of about 1% active surface with electroactive "pieces" of micrometer dimensions are anticipated to yield detection limits of about 1 fmol injected into a typical packed-column liquid chromatograph. This corresponds to about 10(-10) M analyte in the detector and about an order of magnitude improvement over solid electrodes.
MeSH term(s)	Electrochemistry ; Microelectrodes
Language	English
Publishing date	1989-02-15
Publishing country	United States
Document type	Journal Article ; Research Support, U.S. Gov't, P.H.S.
ZDB-ID	1508-8
ISSN	1520-6882 ; 0003-2700
ISSN (online)	1520-6882
ISSN	0003-2700
DOI	10.1021/ac00179a004
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Article: Prediction of molecular recognition-enhanced phenobarbital extraction based on solvatochromic analysis.

Sun, L / Weber, S G

Journal of molecular recognition : JMR

1998 Volume 11, Issue 1-6, Page(s) 28–31

Abstract: The extraction efficiency for organic molecules using synthetic receptors is highly dependent on solvent properties. Solvent influences the partitioning of both the desired compound and the interfering species. Solvent also influences the solubility of ... ...

Abstract	The extraction efficiency for organic molecules using synthetic receptors is highly dependent on solvent properties. Solvent influences the partitioning of both the desired compound and the interfering species. Solvent also influences the solubility of the receptor and its affinity for the substrate. Therefore the free energy involved in extraction can be optimized by using a carefully selected solvent. In this paper we demonstrate the use of a solvatochromic model to predict the influence of solvent dipolarity, H-bond acidity and H-bond basicity on selectivity and yield of phenobarbital extraction. We also used this method to estimate the purity and yield of phenobarbital extraction in 12 poly(vinyl chloride) plasticizers and solvents. This approach can be generalized for assisting the selection of optimal solvent and provide insight into the rational design of solvent and receptor for industrial extractions.
MeSH term(s)	Drug Contamination ; Hydrogen Bonding ; Phenobarbital/analysis ; Phenobarbital/isolation & purification ; Plasticizers ; Solvents ; Thermodynamics
Chemical Substances	Plasticizers ; Solvents ; Phenobarbital (YQE403BP4D)
Language	English
Publishing date	1998
Publishing country	England
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	1015084-5
ISSN	1099-1352 ; 0952-3499
ISSN (online)	1099-1352
ISSN	0952-3499
DOI	10.1002/(SICI)1099-1352(199812)11:1/6<28::AID-JMR385>3.0.CO;2-H
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Zs.A 2954: Show issues

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Article: Chromatographic band broadening theory using a random walk with a step-length distribution.

Weber, S G

Analytical chemistry

1984 Volume 56, Issue 12, Page(s) 2104–2109

MeSH term(s)	Chromatography/instrumentation ; Mathematics
Language	English
Publishing date	1984-10
Publishing country	United States
Document type	Journal Article ; Research Support, U.S. Gov't, P.H.S.
ZDB-ID	1508-8
ISSN	1520-6882 ; 0003-2700
ISSN (online)	1520-6882
ISSN	0003-2700
DOI	10.1021/ac00276a029
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Article: Molecular recognition of phenobarbital in plasticizers equilibrium investigations on the solubility of the barbiturate artificial receptor and its binding to phenobarbital in plasticizers.

Valenta, J N / Weber, S G

Journal of chromatography. A

1996 Volume 722, Issue 1-2, Page(s) 47–57

Abstract: Environmental concern is renewing interest in selective, waste-free extractions. A recent report demonstrated an improved extraction of phenobarbital by means of a specifically designed molecular receptor. In that work, the solvent was CHCl3. The current ...

Abstract	Environmental concern is renewing interest in selective, waste-free extractions. A recent report demonstrated an improved extraction of phenobarbital by means of a specifically designed molecular receptor. In that work, the solvent was CHCl3. The current work is the first step in extending extractions based on molecular recognition to reusable solvents, namely plasticizers. Phenobarbital aqueous/organic partition coefficients, receptor solubility, and phenobarbital-receptor-formation constants in several plasticizers and in their CHCl3 solutions are reported. In addition, by a thermodynamic cycle, the free energy for transfer of the barbiturate-receptor complex from CHCl3 to plasticizers has been calculated. Finally, the data have been displayed in coordinate systems representing extraction efficiency and selectivity. The most selective extraction medium yielding useful extraction efficiency is dioctyl phthalate.
MeSH term(s)	Chemical Phenomena ; Chemistry, Physical ; Hydrogen Bonding ; Indicators and Reagents ; Phenobarbital/chemistry ; Plasticizers/chemistry ; Receptors, Drug/chemistry ; Solubility ; Solvents ; Spectrophotometry, Ultraviolet ; Thermodynamics
Chemical Substances	Indicators and Reagents ; Plasticizers ; Receptors, Drug ; Solvents ; Phenobarbital (YQE403BP4D)
Language	English
Publishing date	1996-01-26
Publishing country	Netherlands
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	1171488-8
ISSN	1873-3778 ; 0021-9673
ISSN (online)	1873-3778
ISSN	0021-9673
DOI	10.1016/0021-9673(95)00689-3
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Article: Detection of bioactive oligopeptides after microbore HPLC with electrochemical detection of their Cu(II) complexes: effect of operating parameters on sensitivity and selectivity.

Chen, J G / Weber, S G

Analytical chemistry

1995 Volume 67, Issue 19, Page(s) 3596–3604

Abstract: We used a microbore reversed phase column for acetonitrile/0.1% aqueous TFA gradient elution separation of peptides with the detection of their copper complexes by electrochemical detection. The copper complexes are formed in a short (1 or 1.5 min) ... ...

Abstract	We used a microbore reversed phase column for acetonitrile/0.1% aqueous TFA gradient elution separation of peptides with the detection of their copper complexes by electrochemical detection. The copper complexes are formed in a short (1 or 1.5 min) postcolumn reactor following mixing of the eluent with the postcolumn reaction phase. Detection can be at an upstream anode or a downstream cathode of a dual-electrode electrochemical detector. The following parameters have been investigated for their effect on the sensitivity and the selectivity of the procedure: postcolumn pH, buffer type, temperature, reaction time, and anode potential. Of the 23 bioactive peptides used, there are several that fall into classes according to their chemical and electrochemical behavior with copper(II): those with a blocked terminal amine, those with aspartate in the third position, those that have an electroactive amino acid, and those that have a cyclic structure formed by the amide backbone through a Cys-Cys disulfide bridge. Depending on these attributes, the operating parameters have an influence on the sensitivity of the determination. Among the more well-defined results are the following. Uncomplicated peptides with a free amine terminus react rapidly in the postcolumn reactor and give signals in the range predicted by theory. There is evidence that longer peptides, and those with a blocked amine terminus, have a sensitivity limited by kinetic factors. The oxidations of tyrosine and tryptophan in peptides are dramatically influenced by buffer type at pH 9.8. At pH 8.0, there is no signal from several peptides in phosphate buffer, while in borate there is a signal.
MeSH term(s)	Amino Acid Sequence ; Chromatography, High Pressure Liquid ; Copper/chemistry ; Electrochemistry ; Molecular Sequence Data ; Oligopeptides/analysis
Chemical Substances	Oligopeptides ; Copper (789U1901C5)
Language	English
Publishing date	1995-10-01
Publishing country	United States
Document type	Journal Article ; Research Support, U.S. Gov't, P.H.S.
ZDB-ID	1508-8
ISSN	1520-6882 ; 0003-2700
ISSN (online)	1520-6882
ISSN	0003-2700
DOI	10.1021/ac00115a033
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Article: Carbonized microcellular foam-based porous flow-through electrodes with unit coulometric efficiency.

Davis, B K / Weber, S G

Analytical chemistry

1994 Volume 66, Issue 7, Page(s) 1204–1207

Abstract: The carbon foam used was pyrolyzed from PAN at 1100 degrees C. Its specific surface area is 21,000 cm-1 and its porosity is 0.97; thus, it is ideally suited for coulometric cells. Although the material is fragile, it can be bored with steel or glass ... ...

Abstract	The carbon foam used was pyrolyzed from PAN at 1100 degrees C. Its specific surface area is 21,000 cm-1 and its porosity is 0.97; thus, it is ideally suited for coulometric cells. Although the material is fragile, it can be bored with steel or glass tubing. The most effective cells consisted of cylindrical segments of foam which were from 0.5 to 3.0 mm long inside of a 1.0 mm in diameter glass tube. In the smallest cell, 0.5 mm long, the electrode volume was 0.4 microL, yet it yielded unit coulometric efficiency at 1.0 mL/min. The pressure required for higher flow rates caused electrode failure. Longer electrodes yielded cells with unit coulometric efficiency up to the system limits near 3 mL/min.
MeSH term(s)	Carbon ; Electrochemistry ; Electrodes ; Surface Properties
Chemical Substances	Carbon (7440-44-0)
Language	English
Publishing date	1994-04-01
Publishing country	United States
Document type	Journal Article ; Research Support, U.S. Gov't, P.H.S.
ZDB-ID	1508-8
ISSN	1520-6882 ; 0003-2700
ISSN (online)	1520-6882
ISSN	0003-2700
DOI	10.1021/ac00079a041
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