"Retention projection" enables reliable use of shared gas chromatographic retention data across laboratories, instruments, and methods.

Gas chromatography/mass spectrometry (GC/MS) is a primary tool used to identify compounds in complex samples. Both mass spectra and GC retention times are matched to those of standards; however, it is often impractical to have standards on hand for every compound of interest, so we must rely on shared databases of MS data and GC retention information. Unfortunately, retention databases (e.

An Advanced, Interactive, High-Performance Liquid Chromatography Simulator and Instructor Resources.

High-Performance Liquid Chromatography (HPLC) simulation software has long been recognized as an effective educational tool, yet we found that existing HPLC simulators are either too expensive, out-dated, or lack many important features we deemed necessary to make them widely useful for educational purposes. Here we describe a free, open-source HPLC simulator we developed that we believe meets this need. The web-based simulator is uniquely sophisticated, yet accessible to a diverse user group with varied expertise in HPLC.

Identifying orthogonal and similar reversed phase liquid chromatography stationary phases using the system selectivity cube and the hydrophobic subtraction model.

We have compared over 500 RPLC columns characterized by the hydrophobic subtraction model using the system selectivity cube (SSC). We have shown numerous differences in column selectivity even among columns in the same class (e.g.

Chromatographic selectivity triangles.

2010 marked the 50th anniversary of the use of selectivity triangles to characterize chromatographic phases. Such plots ultimately identify and quantify the blend of intermolecular interactions that occur between solutes and solvents/phases. The first chromatographic triangle was proposed by Brown and applied to GC stationary phases.

System selectivity cube: a 3D visualization tool for comparing the selectivity of gas chromatography, supercritical-fluid chromatography, high-pressure liquid chromatography, and micellar electrokinetic capillary chromatography systems.

A three-dimensional visualization tool termed the system selectivity cube (SSC) has been developed to aid in the selection of chromatography systems. The most effective way to change the resolution of a complex mixture is to change the selectivity of the separation. The SSC allows efficient identification of systems of differing selectivity.

Orientational polarisability of lipid membrane surfaces.

Here we present a fluorescence method based on the Stokes shift of the voltage-sensitive dye di-8-ANEPPS to quantify the orientational polarisability of lipid membrane surfaces, i.e. the polarisability due to molecular reorientation.

Comparison of excitation and emission ratiometric fluorescence methods for quantifying the membrane dipole potential.

We are interested in developing fluorescence methods for quantifying lateral variations in the dipole potential across cell surfaces. Previous work in this laboratory showed that the ratio of fluorescence intensities of the voltage-sensitive dye di-8-ANEPPS using excitation wavelengths at 420 and 520 nm correlates well with measurements of the dipole potential. In the present work we evaluate the use of di-8-ANEPPS and an emission ratiometric method for measuring dipole potentials, as Bullen and Saggau (Biophys.

Cholesterol effect on the dipole potential of lipid membranes.

The effect of cholesterol removal by methyl-beta-cyclodextrin on the dipole potential, psi(d), of membrane vesicles composed of natural membrane lipids extracted from the kidney and brain of eight vertebrate species was investigated using the voltage-sensitive fluorescent probe di-8-ANEPPS. Cyclodextrin treatment reduced cholesterol levels by on average 80% and this was associated with an average reduction in psi(d) of 50 mV. Measurements of the effect of a range of cholesterol derivatives on the psi(d) of DMPC lipid vesicles showed that the magnitude of the effect correlated with the component of the sterol's dipole moment perpendicular to the membrane surface.

Mechanistic implications of the equality of compensation temperatures in chromatography.

A common interpretation of the observation that two processes exhibit similar compensation temperatures in an enthalpy-entropy plot is that the two processes occur via the same "mechanism". We show that this interpretation is not rigorously allowed. In fact, the only thing that can be concluded from the observation of identical compensation temperatures is that the relative contributions of enthalpy and entropy to the overall free energy are the same in the two processes.