Biomedical subjects

Robert Arnell

Publications and source records attributed to Robert Arnell.

4 recordsLinked to original sources

PubMed2006

Validation of the tracer-pulse method for multicomponent liquid chromatography, a classical paradox revisited.

The tracer-pulse method was extended and validated for the determination of multicomponent adsorption isotherms in liquid chromatography. Competitive adsorption isotherms can be determined for any number of solutes, up to the column resolution limit. The basic principle is to equilibrate the column with an eluent containing a mixture of the solutes and then measure the migration velocity of each of them through the column. It is easy to calculate the stationary phase concentrations from these velocities, given the eluent composition. As in frontal analysis, real competitive isotherm data are measured using this method, unlike other methods, which only produce parametric estimates. The method was used to measure the binary isotherms of beta-blockers on a Kromasil C8 column. The data were fitted to competitive bi-Langmuir adsorption isotherm functions and was found to agree well with the results of frontal analysis and the perturbation method. Computer simulations based on the isotherm parameters were performed and displayed very good agreement with the experimental chromatograms. An intriguing and seemingly paradoxical property is visualized and discussed: the fact that the injected molecules are not found in the detected peaks.

Journal Article↗

PubMed2006

Invisible analyte peak deformations in single-component liquid chromatography.

It is well known that if a small excess of solute is injected into a chromatographic system equilibrated with an eluent containing the same solute, a single so-called perturbation peak will appear in the chromatogram. It was recently shown (Samuelsson, J.; Forssén, P.; Stefansson, M.; Fornstedt, T. Anal. Chem. 2004, 76, 953-958) that this peak consists of displaced plateau molecules; the injected molecules (mass peak) elute later, together with a deficiency of plateau molecules and are therefore not detected. In this article, we investigated what happens if a large rather than a small excess of solute molecules is injected. To study this systematically, the experimental method involved an enantiomer pair in an achiral separation system. It was found that the invisible mass peak was extremely deformed and that its shape depended on the amount of excess injected, the eluent concentration, and the column length. Depending on these operational conditions, the mass peak changed from a classical Langmuirian (tailing) to an anti-Langmuirian (leading) shape, with deformed shapes observable in the transition. The visible, overloaded perturbation peak was always Langmuirian, regardless of the mass peak shape.

Journal Article↗

PubMed2006

Analytical characterization of chiral drug-protein interactions: comparison between the optical biosensor (surface plasmon resonance) assay and the HPLC perturbation method.

Two modern, fundamentally different methods were used for a detailed investigation of enantioselective drug-protein interactions, a surface plasmon resonance (SPR)-based Biacore 2000 biosensor assay and the previously validated HPLC perturbation method (HPLC-PM). This is the first time SPR has been used for this purpose. The fundamental features of the two methods were investigated, and the consequences for operation and data evaluation were addressed. With HPLC-PM, chiral data could be obtained directly from the racemic mixture, whereas a separate analysis of each pure enantiomer was required to obtain chiral data with SPR. It was shown that if chirality is not attributed in the SPR analysis, misleading average racemic binding constants will be obtained. Both drug and protein consumption were considerably higher with HPLC-PM. HPLC-PM was found to be best suited for measurements of weak affinity interactions, whereas the SPR method was best for strong interactions. With both methods, the presence of DMSO in the samples severely affected the interactions, introducing errors. The binding of the beta-blockers alprenolol and propranolol to Cel7a cellulase was used as a model system. These methods gave results that agreed quite well qualitatively, but considerable quantitative deviations were sometimes obtained.

Adrenergic beta-Antagonists↗

PubMed2005

Accurate and rapid estimation of adsorption isotherms in liquid chromatography using the inverse method on plateaus.

The inverse method (IM) is an attractive approach for estimating adsorption isotherm parameters in liquid chromatography (LC), mainly due to its experimental simplicity and low sample consumption. This article presents a new experimental approach, the inverse method on plateaus (IMP), which uses elution profiles on concentration plateaus together with IM. This approach enabled us to obtain very accurate adsorption isotherms that agreed well with those estimated by means of frontal analysis over the entire concentration range under consideration. IMP is recommended when accurate adsorption isotherm estimates are required, and standard IM is insufficient.

Adsorption↗