I am a retired research scientist, continuing to work as an independent scholar. While I previously published technical papers on diverse subjects related to chemistry and biophysics, more recent work concerns issues of epistemology.email: martin.potschka at gmx.at
The flow of polyclectrolytes through microporous matrices has been studied with several rigid res... more The flow of polyclectrolytes through microporous matrices has been studied with several rigid resins including ion-exchange columns in a variety of aqueous buffers differing in composition, pH and ionic strength. The elution of native proteins having well defined structures was measured at very low polymer concentrations in the presence of sufficient supporting electrolyte to exclude kinetic interaction phenomena and Donnan-type interactions amongst the solute molecules. It was found to depend strongly on ionic strength, I, without parallel effects in the bulk properties; the effective radii increased in proportion to I−1/2. It is concluded that size-exclusion chromatography (SEC) measures the unperturbed dimensions of a polyelectrolyte which include the surrounding diffuse double layer and any other interactions of the solvent. Chromatography thereby provides a novel approach for the measurement of electrostatic and colloidal properties of macromolecules and of solvation. The bulk viscosity-determined molecular radii, i.e., the size and shape excluding the double layer, are obtained even at low ionic strength either by calibration with similarly charged polyelectrolytes or by extrapolation to high ionic strength. Universal SEC calibration was also achieved on ion-exchange columns. Understanding the physical basis of SEC in view of the results of the present study may provide a new method for characterization of the structure and formation of gel networks.
Abstract The retention volume in size-exclusion chromatography (SEC) depends on both the size of ... more Abstract The retention volume in size-exclusion chromatography (SEC) depends on both the size of the particle proper and the interfacial mutual repulsion of the surfaces, i.e., between the pore wall and the surface of the particles. The presence of some interfacial repulsion is crucial to obtain a pure SEC mode of elution. It is therefore always present and should not be neglected as is usually done. Analysis of published data shows that the interfacial repulsion is well described by the Dejaguin—Landau—Verwey—Overbeek (DLVO) theory of colloidal stability, and its properties can therefore be studied in detail via chromatography. It is shown that interfacial repulsion depends on the size of the latex beads ans attains large values for larger beads. For a given size of the bead it depends strongly on its charge up to a limit of saturation, as predicted by DLVO theory.
Abstract Based on experimental evidence, this paper establishes a proper theory of obstructed dif... more Abstract Based on experimental evidence, this paper establishes a proper theory of obstructed diffusion which includes the behaviour of polyelectrolytes at low ionic strength and has relevance far beyond chromatography. In addition, it establishes the role of convection in the chromatographic transport process within the porous matrix, which consequently is totally porous and filled with a slowly moving “stagnant” zone. Convection is a crucial factor for the high resolution of modern HPLC columns and size-exclusion chromatographic analysis of ultra-large polymers would be impossible otherwise. Convection processes in the mobile and stagnant zones, of course, are related and a proper description of eddy dispersion thus facilitates understanding of the process within the pores. The processes of dispersion and retention are demonstrated to be governed by different measures of size which delimits the role of transport processes in the mechanism of retention and provides information on the asymmetry of polymer shape by the same experiment. The comprehensive interpretation of chromatographic dispersion facilitates a priori modelling of resolution, improves size distribution analysis via straightforward correction of physical dispersion and certainly enriches our physical intuition. With few exceptions, the C-term of the Van Deemter equation for SEC hs been exclusively analysed as a diffusion problem. All data on obstructed diffusion obtained from SEC thus lack consideration of convective mass transport, and most were superficial in their treatment of mobile zone factors. To document the role of convection in a model-independent manner, experimental dispersion data are initially analysed with a combination of eqns. 4, 5, 10, 12, 15, 16, 21 and 22. Eqn. 22 eventually will be replaced by eqn. 29 in the Results section. Convective transport modifies Dpore and application of eqn. 22 or 29 alone consequently leads to superficially low apparent α values. In this manner the occurrence of convection is easily recognized. Subsequent complete analysis (which is deferred to the second part of the Discussion) then will add eqn. 31 to the above list and test the validity of various proposed theories for Cc (eqns. 30, 33, 36 and 37) with the constraint that the α value should become universal.
... 1999, 2004; Berlinski 1996, 2001; Wells 2000; Campbell & Meyer 2003; Denton 1985, 1998 ..... more ... 1999, 2004; Berlinski 1996, 2001; Wells 2000; Campbell & Meyer 2003; Denton 1985, 1998 ... In a way one might say that science has grown self-sufficient, but only if ... evolution from a single unique origin (corollary to #5). 7. Hierarchical organization and compartmentalization of ...
Summary: This article reviews some recent developments on the determination of the Band Broadenin... more Summary: This article reviews some recent developments on the determination of the Band Broadening Function (BBF) in Size Exclusion Chromatography (SEC) of polymers. It was carried out in the frame of the IUPAC Project: ''Data Treatment in Size Exclusion Chromatography of Polymers''. The correction for band broadening (BB) is important for quantitative determinations of the molar mass distribution (MMD) of narrow-distributed (or highly multimodal) polymers, and of derived variables such as kinetic parameters. In the narrow range of a molar mass standard, the BBF is uniform and of positive skewness. In a broad chromatographic range, the BBF is non-uniform and skewed; and it can be adequately represented by an exponentially-modified Gaussian function (EMG) of 2 parameters that vary slightly with elution volume: an increasing Gaussian variance and a decreasing exponential decay. Additionally, the total BBF variance remains almost constant if not close to the total e...
Neodarwinism has been challenged along two lines. One, by Creationists who take a literal reading... more Neodarwinism has been challenged along two lines. One, by Creationists who take a literal reading of the Bible; such a-historical interpretations of the scriptures are not endorsed by the Roman Catholic Church and most other denominations. The second line focuses on intelligent design, claiming that there is evidence for irreducible complexity that only by executing a preexisting intelligent blueprint could have been provided. [Paley 1802; Johnson 1991, 2000;
A main concern and widespread source of mutual misunderstanding [that has not been resolved in th... more A main concern and widespread source of mutual misunderstanding [that has not been resolved in the exchange between Searle, Bromberger, Pinker and Chomsky in the New York Review of Books in 2002] are the innate vs. social characteristics of language capacity and its constitutive rules. Hence, whether we approach the foundations of mind in the manner of natural sciences (as Chomsky prefers) or whether they belong to the Humanities, specifically – are matters for the social sciences (as Searle insists). This dichotomy follows the tradition of C. P. Snow’s “two cultures”. Hence the topic expressed in the title line has two dimensions: firstly the fields of study that one may consider appropriate to explore the subject; it is this matter that then often substitutes for a second more fundamental question concerning differences between social and genetic modes of determination. My arguments are guided by the ideas raised in this exchange and do not claim to exhaust the subject of language...
Examines size exclusion chromatography technology from both the detector-focused and column-focus... more Examines size exclusion chromatography technology from both the detector-focused and column-focused approaches. Provides fundamental information on the mechanism of size exclusion chromatography Reparations. Addresses special topics in size exclusion chromatography, including characterization of copolymers, inverse size exclusion chromatography, aggregating polymers, polysaccharides, and proteins.
The flow of polyclectrolytes through microporous matrices has been studied with several rigid res... more The flow of polyclectrolytes through microporous matrices has been studied with several rigid resins including ion-exchange columns in a variety of aqueous buffers differing in composition, pH and ionic strength. The elution of native proteins having well defined structures was measured at very low polymer concentrations in the presence of sufficient supporting electrolyte to exclude kinetic interaction phenomena and Donnan-type interactions amongst the solute molecules. It was found to depend strongly on ionic strength, I, without parallel effects in the bulk properties; the effective radii increased in proportion to I−1/2. It is concluded that size-exclusion chromatography (SEC) measures the unperturbed dimensions of a polyelectrolyte which include the surrounding diffuse double layer and any other interactions of the solvent. Chromatography thereby provides a novel approach for the measurement of electrostatic and colloidal properties of macromolecules and of solvation. The bulk viscosity-determined molecular radii, i.e., the size and shape excluding the double layer, are obtained even at low ionic strength either by calibration with similarly charged polyelectrolytes or by extrapolation to high ionic strength. Universal SEC calibration was also achieved on ion-exchange columns. Understanding the physical basis of SEC in view of the results of the present study may provide a new method for characterization of the structure and formation of gel networks.
Abstract The retention volume in size-exclusion chromatography (SEC) depends on both the size of ... more Abstract The retention volume in size-exclusion chromatography (SEC) depends on both the size of the particle proper and the interfacial mutual repulsion of the surfaces, i.e., between the pore wall and the surface of the particles. The presence of some interfacial repulsion is crucial to obtain a pure SEC mode of elution. It is therefore always present and should not be neglected as is usually done. Analysis of published data shows that the interfacial repulsion is well described by the Dejaguin—Landau—Verwey—Overbeek (DLVO) theory of colloidal stability, and its properties can therefore be studied in detail via chromatography. It is shown that interfacial repulsion depends on the size of the latex beads ans attains large values for larger beads. For a given size of the bead it depends strongly on its charge up to a limit of saturation, as predicted by DLVO theory.
Abstract Based on experimental evidence, this paper establishes a proper theory of obstructed dif... more Abstract Based on experimental evidence, this paper establishes a proper theory of obstructed diffusion which includes the behaviour of polyelectrolytes at low ionic strength and has relevance far beyond chromatography. In addition, it establishes the role of convection in the chromatographic transport process within the porous matrix, which consequently is totally porous and filled with a slowly moving “stagnant” zone. Convection is a crucial factor for the high resolution of modern HPLC columns and size-exclusion chromatographic analysis of ultra-large polymers would be impossible otherwise. Convection processes in the mobile and stagnant zones, of course, are related and a proper description of eddy dispersion thus facilitates understanding of the process within the pores. The processes of dispersion and retention are demonstrated to be governed by different measures of size which delimits the role of transport processes in the mechanism of retention and provides information on the asymmetry of polymer shape by the same experiment. The comprehensive interpretation of chromatographic dispersion facilitates a priori modelling of resolution, improves size distribution analysis via straightforward correction of physical dispersion and certainly enriches our physical intuition. With few exceptions, the C-term of the Van Deemter equation for SEC hs been exclusively analysed as a diffusion problem. All data on obstructed diffusion obtained from SEC thus lack consideration of convective mass transport, and most were superficial in their treatment of mobile zone factors. To document the role of convection in a model-independent manner, experimental dispersion data are initially analysed with a combination of eqns. 4, 5, 10, 12, 15, 16, 21 and 22. Eqn. 22 eventually will be replaced by eqn. 29 in the Results section. Convective transport modifies Dpore and application of eqn. 22 or 29 alone consequently leads to superficially low apparent α values. In this manner the occurrence of convection is easily recognized. Subsequent complete analysis (which is deferred to the second part of the Discussion) then will add eqn. 31 to the above list and test the validity of various proposed theories for Cc (eqns. 30, 33, 36 and 37) with the constraint that the α value should become universal.
... 1999, 2004; Berlinski 1996, 2001; Wells 2000; Campbell & Meyer 2003; Denton 1985, 1998 ..... more ... 1999, 2004; Berlinski 1996, 2001; Wells 2000; Campbell & Meyer 2003; Denton 1985, 1998 ... In a way one might say that science has grown self-sufficient, but only if ... evolution from a single unique origin (corollary to #5). 7. Hierarchical organization and compartmentalization of ...
Summary: This article reviews some recent developments on the determination of the Band Broadenin... more Summary: This article reviews some recent developments on the determination of the Band Broadening Function (BBF) in Size Exclusion Chromatography (SEC) of polymers. It was carried out in the frame of the IUPAC Project: ''Data Treatment in Size Exclusion Chromatography of Polymers''. The correction for band broadening (BB) is important for quantitative determinations of the molar mass distribution (MMD) of narrow-distributed (or highly multimodal) polymers, and of derived variables such as kinetic parameters. In the narrow range of a molar mass standard, the BBF is uniform and of positive skewness. In a broad chromatographic range, the BBF is non-uniform and skewed; and it can be adequately represented by an exponentially-modified Gaussian function (EMG) of 2 parameters that vary slightly with elution volume: an increasing Gaussian variance and a decreasing exponential decay. Additionally, the total BBF variance remains almost constant if not close to the total e...
Neodarwinism has been challenged along two lines. One, by Creationists who take a literal reading... more Neodarwinism has been challenged along two lines. One, by Creationists who take a literal reading of the Bible; such a-historical interpretations of the scriptures are not endorsed by the Roman Catholic Church and most other denominations. The second line focuses on intelligent design, claiming that there is evidence for irreducible complexity that only by executing a preexisting intelligent blueprint could have been provided. [Paley 1802; Johnson 1991, 2000;
A main concern and widespread source of mutual misunderstanding [that has not been resolved in th... more A main concern and widespread source of mutual misunderstanding [that has not been resolved in the exchange between Searle, Bromberger, Pinker and Chomsky in the New York Review of Books in 2002] are the innate vs. social characteristics of language capacity and its constitutive rules. Hence, whether we approach the foundations of mind in the manner of natural sciences (as Chomsky prefers) or whether they belong to the Humanities, specifically – are matters for the social sciences (as Searle insists). This dichotomy follows the tradition of C. P. Snow’s “two cultures”. Hence the topic expressed in the title line has two dimensions: firstly the fields of study that one may consider appropriate to explore the subject; it is this matter that then often substitutes for a second more fundamental question concerning differences between social and genetic modes of determination. My arguments are guided by the ideas raised in this exchange and do not claim to exhaust the subject of language...
Examines size exclusion chromatography technology from both the detector-focused and column-focus... more Examines size exclusion chromatography technology from both the detector-focused and column-focused approaches. Provides fundamental information on the mechanism of size exclusion chromatography Reparations. Addresses special topics in size exclusion chromatography, including characterization of copolymers, inverse size exclusion chromatography, aggregating polymers, polysaccharides, and proteins.
A variety of applications depend on accurate knowledge and quality control of polymer mass (or si... more A variety of applications depend on accurate knowledge and quality control of polymer mass (or size) distribution, its mean, moments and even details. Not true molecular masses are what necessarily counts, but avoiding uncontrolled variations in whatever parameter is measured to anticipate performance of a product upon application. Size exclusion chromatography is still a common means for characterization of polymer mixtures. Of its varied methodological limitations one is the systematic distortion imposed by the dynamic process of peak dispersion. In theory correcting a chromatogram for instrumental band broadening is straightforward and the task is considered to be solved at least in principle. However, failure of a previous generation of practical implementations to perform to expectation has diminished trust in such correction procedures altogether. If we agree that it is at all meaningful to devise a general procedure for band broadening correction, which is independent of the chemical properties of a particular analyte and column, we have to design it with the following performance in mind:-) objective validation criteria: a fully automated implementation that is independent of an operators educated guesses and algorithmic interventions;-) uncompromising numerical techniques that match modern computing facilities yet are fast enough for on-line implementation;-) undemanding on the part of application chemists: column related performance parameters have to be identified such that a vendor of SEC prepacked columns is capable to provide them with minimal effort;-) open modular design capable to accommodate future technical and scientific advances into the procedure. It should also aim to be otherwise compatible with existing (commercial and non-commercial) chromatographic analysis software. These demands exclude most published schemes, notably Fast-Fourier-Transforms, but can be met by +) restricting data acquisition to equidistant sampling intervals-Tung's integral equation then becomes a linear matrix problem; +) combined with computing the number of independent parameters (rank) from the S/N of actual experimental data (it remains an ill-conditioned numeric problem); +) decomposing the data reduction and transformation matrix into two terms, for one: assuming that peak shape (tailing) is independent of retention time and provided without prejudice from an experimentally measured reference (small organic molecules, D 2 O; even solvent peak?) and scaling its peak width as required-or alternatively by formulating reasonable algorithmic approximations (e.g. skewed gaussians) from first principles and validating them; +) for the other part: assuming that peak width (dispersion), which is not a constant but varies with retention time in complicated ways, can be expressed in algorithmic form to a sufficient degree of accuracy and independent of matrix properties and column packing except for certain well defined and independently measured column-specific parameters. This was Van Deemters problem and even today the general theoretical problem of transport in packed porous beads is not once-and-forever solved in all details;
Neodarwinism has been challenged along two lines. One, by Creationists who take a literal reading... more Neodarwinism has been challenged along two lines. One, by Creationists who take a literal reading of the Bible; such a-historical interpretations of the scriptures are not endorsed by the Roman Catholic Church and most other denominations. The second line focuses on intelligent design, claiming that there is evidence for irreducible complexity that only by executing a preexisting intelligent blueprint could have been provided.
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