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P W Carr

Publications and source records attributed to P W Carr.

At least 19 recordsLinked to original sources
PubMed1994

High-performance anion exchange of small anions with polyethyleneimine-coated porous zirconia.

The preparation and chromatographic characterization of an ion-exchange high-performance liquid chromatographic support by deposition and crosslinking of polyethyleneimine (PEI) on the surface of porous zirconia is described. Adsorption and evaporation methods were used for coating PEI onto the zirconia particles. These two stationary phases were compared by elemental analysis, ion-exchange capacity and by chromatography. High efficiency and good selectivity were observed for inorganic and organic anions. The addition of a strong, hard Lewis base to the mobile phase dramatically improved the peak shape and efficiency of para benzoic acid derivatives. PEI-coated zirconia showed a distinct elution sequence for organic anions when compared to bare zirconia or silica-based phases. The polyamine coated zirconia was stable over a pH range from 2.75 to 9. Flow studies, using nitrite as a probe solute, showed that both coating procedures produced packed columns with good mass-transfer properties.

Anions↗
PubMed1994

Easily regenerable affinity chromatographic zirconia-based support with concanavalin A as a model ligand.

The goal of this work was to develop a generic approach for producing affinity chromatographic columns which can be regenerated. Concanavalin A (Con A) was immobilized adsorptively by an in situ method onto a zirconium dioxide (zirconia) chromatographic support and used to resolve chromophorically labeled monosaccharides. The Con A was then removed from the zirconia by flushing with base. The same column was regenerated by applying a fresh aliquot of Con A. This cycle was repeated several times to demonstrate consistency in the loading capacity and the stability of the underlying zirconia support. Finally we used glutaraldehyde to cross-link the Con A to increase the long-term stability of the column. Hydrolyzing the protein with acid allowed it to be removed under alkaline conditions and the column regenerated simply by adding more Con A followed by glutaraldehyde cross-linking.

Adsorption↗
PubMed1994

Liquid chromatographic study of solute hydrogen bond basicity.

The purpose of the present work was to investigate a liquid chromatographic method for the measurement of relative hydrogen bond basicities of dilute species. This type of determination cannot be done with conventional reversed-phase liquid chromatography due to the silanophilic interactions of basic solutes with the silica packing material. The studies were done on a polymeric stationary phase with pendant phenol groups that act as powerful hydrogen bond donors. Solute retention was evaluated in terms of two hydrogen bond basicity scales, beta 2H and beta 2C, and a steric hindrance parameter, Es. beta 2H and beta 2C are basicity scales based on the free energy of forming 1:1 hydrogen bond complexes and the retention on a strong hydrogen bond donor gas chromatographic phase, respectively. The Es parameter characterizes the steric effect experienced by the solute acceptor site. It is shown that retention correlates very strongly with beta 2H and less strongly with beta 2C. The log k' values need only two descriptive parameters, i.e., beta 2H and Es, to give a good fit. As a whole, retention on the phenolic polymeric phase provides an efficient method for the measurement of relative hydrogen bond basicities.

Alcohols↗
PubMed1994

Study of the irreversible adsorption of proteins on polybutadiene-coated zirconia.

The cause of irreversible adsorption of proteins on polybutadiene-coated zirconia is investigated by comparing the chromatographic properties of polybutadiene-coated zirconia with that of other reversed-phase packing materials such as bonded phase silica, polybutadiene-coated alumina and polybutadiene-coated silica. We find that the polybutadiene-coated zirconia has a micropore size distribution similar to that of the polybutadiene-coated alumina, from which some proteins can be eluted. Thus, the irreversible adsorption of proteins on polybutadiene-coated zirconia is not caused by entrapment of proteins in the micropores of the packing. The high hydrophobicity of the polybutadiene coating and the strong Lewis acid sites on the zirconia surface cause strong interactions between proteins and the stationary phase, the combination of which lead to irreversible adsorption of proteins on polybutadiene-coated zirconia.

Adsorption↗
PubMed1993

Chemistry of zirconia and its use in chromatography.

The purpose of this review is to shed some light on the complex properties of zirconia's surface chemistry in order to better understand its behaviour under chromatographic conditions. We emphasize the great differences between the much better known chemistry of a silica surface and the chemistry of zirconia's surface. The review describes both the physical and chemical properties of zirconium dioxide from a chromatographic point of view. The chemistry of monoclinic zirconia surface is developed from its underlying crystalline structure. The paper describes the dependence of the specific surface area, pore volume, porosity and mechanical strength on thermal treatment. Methods of synthesis of chromatographically useful zirconia are outlined. The review also covers the adsorption properties of zirconia at both gas-solid and liquid-solid interfaces. Adsorption of water, carbon dioxide, carbon monoxide and ammonia are described and the controversies concerning the surface concentration of adsorption sites are presented. The complex chemistry of a zirconia surface is pointed out and the importance of ligand exchange reactions is emphasized. In contrast to a silica surface, ligand exchange plays an important role in liquid chromatographic applications of zirconia. Strong, hard Lewis acid sites, present on a zirconia surface, can interact with hard Lewis bases and these interactions, sometimes troublesome, can be successfully exploited even for protein separations. Zirconia's surface can be modified in many ways: dynamically, by addition of competing Lewis bases to the mobile phase, or permanently, by covering its surface with polymers or by depositing carbon. The review also shows that the main difficulty in achieving a wider variety of applications is probably our lack of knowledge and poor understanding of zirconia's surface chemistry.

Chromatography↗
PubMed1992

The role of Lewis acid-base processes in ligand-exchange chromatography of benzoic acid derivatives on zirconium oxide.

Porous microparticulate zirconium oxide shows very different selectivities and pH dependencies for the separation of benzoic acid derivatives than do conventional bonded-phase anion-exchange supports. This results from a very significant ligand-exchange contribution to the retention of hard Lewis bases on the surface of transition-metal oxide supports. We have found that the capacity factors of a wide variety of derivatives of benzoic acid are closely correlated with their Bronsted acidities. The eluent pH is also a critical factor in determining the magnitude of the capacity factor, but it does not have much influence on chromatographic selectivity. The differential selectivity of this phase in comparison to conventional polymeric and bonded-phase anion exchangers can be attributed to complexation and steric effects which profoundly alter the elution patterns of certain solutes.

Benzoates↗
PubMed1992

Development of an eluotropic series for the chromatography of Lewis bases on zirconium oxide.

Ligand-exchange interactions, which dominate the retention characteristics of Lewis base solutes on zirconium oxide, can be strongly attenuated by the addition of a competing Lewis base to the eluent. The chromatographic effects of these competing bases vary significantly in their thermodynamics and kinetics depending on their structure and Lewis basicity. An eluotropic scale of mobile-phase strength for ligand-exchange/ion-exchange chromatography on zirconia has been developed which ranks the overall elution strength of a variety of Lewis bases in terms of their ability to elute a wide variety of benzoic acid derivatives. This series generally holds true for similar solutes; however, deviations are noted with some solutes and eluents where chelation and steric factors alter the kinetic and thermodynamic characteristics of the retention process.

Benzoates↗
PubMed1992

Ion- and ligand-exchange chromatography of proteins using porous zirconium oxide supports in organic and inorganic Lewis base eluents.

The applicability of an eluotropic scale pertaining to the desorption of low molecular weight Lewis base solutes from zirconium oxide is examined for its ability to rationalize the retention of proteins on this substrate. The strongest Lewis base eluents (phosphate and fluoride) are able to bring about elution of nearly all proteins provided that their initial mobile phase concentration almost saturates the eluent's adsorption isotherm. In contrast, weaker Lewis bases such as borate, sulfate and bromide are able to elute only those proteins which are retained primarily by ionic interactions. In weak eluents, proteins that contain a large number of accessible Lewis base sites are not eluted from the support. The effect of ionic strength and a variety of Lewis base eluents were also examined.

Borates↗
PubMed1991

Chromatographic characterization of a phosphate-modified zirconia support for bio-chromatographic applications.

A phosphate-modified zirconia was investigated for its potential use as a high-performance inorganic cation-exchange support for the separation of proteins. This phosphate modification effectively blocks the sites responsible for the strong interactions of certain Lewis bases with the zirconia surface. It provides a more "bio-compatible" stationary phase, resulting in high recoveries for proteins and enzymes and retention of their enzymatic activity. The stability, loading capacity, selectivity, efficiency and separation mechanism on the phosphate-modified zirconia are reported. These studies have shown that phosphate-modified zirconia is a useful high-performance ion-exchange support for the separation of cationic proteins and for blocking the sites responsible for the high affinity of zirconia towards certain anions. This makes the phosphate modification interesting in its own right and as an intermediate stage for the development of other zirconia-based chromatographic supports.

Chromatography, Ion Exchange↗
PubMed1991

Preliminary assessment of removal of pyrogenic lipopolysaccharides with colloidal zirconia adsorbents.

Preliminary evaluation of bare or polymer-coated colloidal monoclinic zirconia of nominal particle size 100 nm indicated that it is an effective adsorbent for pyrogenic lipopolysaccharides (LPS) as measured by chemical and Limulus amebocyte lysate (LAL) assays. Zirconia at 50 micrograms ml-1 adsorbed 99.95% of added E. coli O128 LPS. Residual LPS levels below 0.1 ng ml-1 were easily attained. Colloidal zirconia was able to remove LPS from solution in the presence of bovine albumin (BSA). Some LPS contaminating BSA lacked affinity for zirconia. Preadsorption of phosphate onto bare zirconia blocked LPS adsorption. However, phosphated-oligomeric glycidyl (epoxy) pentaerythritol-coated colloidal zirconia could be derivatized with imidazole-containing ligands to produce an LPS-binding surface. Preliminary results of adsorption of LPS by the coated particles indicated a reduced level of LPS binding compared to bare zirconia, probably because the particles aggregated during the derivatization process, reducing the effective surface available for LPS adsorption.

Adsorption↗
PubMed1989

Improved resolution of glycoproteins by chromatography with concanavalin A immobilized on microparticulate silica via temperature-programmed elution.

The ability of the column temperature to control elution in the affinity chromatography of glycoproteins (e.g., ovalbumin and horseradish peroxidase) on silica immobilized concanavalin A has been studied. Column temperature programs can be achieved by placing a small HPLC column within a commercial mobile phase preheater assembly. It is shown that elution of adsorbed proteins can be initiated by changing the column temperature without altering the chemical composition of the mobile phase. Further, due to the enhancement in the rate of dissociation of the sample from the ligand, the peaks are narrowed. The resolution can be controlled by changing the initial temperature, dwell time at the initial temperature, and the rate of change of the temperature program. Addition of a competitive binding agent to the mobile phase decreases the temperature needed to elute strongly retained proteins. The effect of heating the column through many thermal cycles is assessed by periodically measuring the retention of a small monosaccharide that binds to the immobilized concanavalin A. The effect of two different immobilization procedures (glutaraldehyde and carbonyldiimidazole), as well as the effect of including a monosaccharide in the mobile phase, on the stability of the column is easily monitored by thermal elution chromatography. The effect of column temperature on the above glycoproteins has been assessed through studies of enzyme activities and anion exchange and isoelectric focusing patterns before and subsequent to temperature-programmed elution affinity chromatography.

Chromatography, Affinity↗
PubMed1987

Solubility properties in biological media 9: prediction of solubility and partition of organic nonelectrolytes in blood and tissues from solvatochromic parameters.

Solubilities in and partition among human blood, brain, lung, kidney, muscle, and fat tissue are well correlated by linear solvation energy relationships of the form: XYZ = XYZo + mVI/100 + s pi + b beta m where XYZ is the logarithm of the solubility property, VI is the intrinsic (van der Waals') molar volume, pi and beta are the solvatochromic parameters that measure solute dipolarity/polarizability and hydrogen-bond acceptor basicity, respectively, and the subscript m indicates that for self-associating compounds, the parameter applies to the non-self-associated "monomer" solute. The equation for log K(brain--blood) indicates that increasing molar volume favors, whereas increasing dipolarity and hydrogen-bond acceptor basicity oppose, solute transfer from blood into brain.

Chemical Phenomena↗
PubMed1986

A radiochemical study of irreversible adsorption of proteins on reversed-phase chromatographic packing materials.

A radiochemical study of the irreversible adsorption of proteins on commercial reversed-phase HPLC packing materials is reported. The conditions of study are similar to those used in HPLC separation of protein. The effects of the amount and contact time of two proteins, ovalbumin and cytochrome c, are reported. Additional results include the effect of column pretreatment with protein, silanophilic mobile-phase blocking agent, and type of packing material on the extent of irreversible adsorption. The loss process is shown to be at least biphasic and the mechanisms of loss distinct for different proteins.

Adsorption↗
PubMed1985

A radiochemical study of irreversible protein loss on high-performance liquid chromatography column frits.

Much success has been achieved in the separation and purification of a wide range of proteins using various high-pressure liquid chromatography techniques. Quantitative analyses of proteins which require 100% mass recovery of the protein are still beset with problems, especially when the total injected amount of protein decreases to below 10 micrograms. Stainless-steel frits have been cited for their deleterious effects on chromatography in general. In addition, the frits have specifically been found to be a significant contributor to irreversible protein loss--particularly when protein sample sizes are on the order of 1 microgram or less. The findings presented below should therefore be of concern to those using HPLC for protein work.

Adsorption↗
PubMed1984

UV visualization of inorganic anions by reversed-phase ion-interaction chromatography: factors that control sensitivity and detection.

This paper describes a chromatographic technique and detection scheme for inorganic anion analysis. Factors that affect sensitivity and detection are discussed, including the concentration and molar absorptivity of the ion-interaction reagent (IIR) as well as the retention of the eluite ion relative to the retention of the system peak. An ideal system will employ a low IIR concentration, so that a detection wavelength corresponding to a high IIR molar absorptivity can be used to monitor the eluites. In addition, eluites that are eluted before the system peak have much lower response factors than those eluted after the system peak. Furthermore, eluites that are not well separated from the system peak have response factors that are many times larger than eluites that are eluted either before or after the system peak. Computer simulations were performed that predict these response factors.

Anions↗
PubMed1984

Ultra-violet visualization of inorganic anions by reversed-phase ion-interaction chromatography; factors that control retention and selectivity.

This paper describes the development and characterization of a separation and detection system for the analysis of mixtures of UV-transparent inorganic anions. Retention and separation occurs when a hydrophobic, positively charged paired-ion chromatography (PIC) reagent or an ion-interaction reagent (IIR) is added to the mobile phase of a reversed-phase system. Detection of UV-transparent ions results from a perturbation of the distribution equilibria of the UV-absorbing IIR upon injection of the sample ions. The effect of factors such as the concentration and nature of the buffer, co-ions and IIR as well as an organic modifier are described. The major advantages of this method are that the system is nearly completely nonspecific, the separation system takes advantage of highly efficient reversed-phase columns, rapid separations of 4-6 anions in approximately 6-7 min and good sensitivity with detection limits of less than 1 nmole injected. In addition, no special equipment is required to perform ion analysis by this technique. Only conventional high-performance liquid chromatography pumps, detectors and reversed-phase columns are required.

Anions↗