An improved method for determining enantiomeric excess by (13)C-NMR in chiral liquid crystal media.

By using a combination of inverse gated (1)H decoupled (13)C-NMR experiments1 with short acquisition times and NMR Cryo-probe technology, the sample requirements and experimental times necessary to accurately measure enantiomeric excess of small chiral molecules has been reduced 16-fold. Quality (13)C-NMR spectra can now be obtained from a 1 to 5 mg sample in 12 minutes. The enantiomeric excess determination achieved from the average integration of all the (13)C-resonances in the spectrum is comparable to enantiomeric excess measured by chiral SFC.

Linear voltage profiles and flow homogeneity in pressurized planar electrochromatography.

Planar electrochromatography (PEC) is an emerging technique for thin-layer chromatography (TLC) where electroosmosis is the driving force for the solvent, not capillary action. This allows for much faster and constant flow rates in turn yielding increased zone capacities and efficiencies. Instrumental designs have changed greatly over the last few years solving many of the initial instrumentation challenges.

Characterization of flow and voltage profiles in planar electrochromatography.

Planar electrochromatography (PEC) is a new technology for thin layer chromatography (TLC) where the separation is driven by electroosmotic forces, not capillary action. This allows for much faster and more efficient chromatography in a planar format. Care needs to be taken when performing these experiments because voltage and flow characteristics can change through a single run, due to buffer gradients, temperature changes (Joule heating) and localized plate heterogeneity.

Column selection for liquid chromatographic estimation of the k'w hydrophobicity parameter.

Newer reversed-phase column technologies that incorporate polar groups either by an endcapping procedure or by embedding them into the stationary phase ligand have been receiving much attention in the literature for their robustness when highly aqueous conditions are used. We investigated their ability to accurately determine the chromatographic hydrophobicity value log k'w. The non-linear deviations of retention data as mobile phase conditions approach zero percent modifier are a large source of error when extrapolating to log k'w values using the linear solvent strength model.