Nanoparticle-based pseudostationary phases in CEC: a breakthrough in protein analysis?

This review focuses on major trends in nanoparticle-based pseudostationary phase (PSP) CEC since the publication of our previous reviews within nanoparticle-based CEC [Nilsson, C., et al., Electrophoresis 2006, 27, 76-83; Nilsson, C., et al., J. Chromatogr. A 2007, 1168, 212-224.]. Special attention is given to the development toward protein analysis, which is driven by the strong emergence of protein drug development in the pharmaceutical industry. Furthermore, we discuss the development in coupling different detection techniques with nanoparticle-based PSP CEC, which were originally predicted to be particularly cumbersome. However, at present, direct UV, LIF and ESI-MS have been used without any severe complications. Different types of nanoparticles used as PSP during the period include gold nanoparticles, carbon nanostructures and lipid-based nanoparticles. New materials (for example, different types of carbon nanostructures and self assembled lipid-based nanostructures) are a strong driving force for development in separation science. Finally, future trends in nanoparticles-based CEC are envisioned.     

X-ray isochromats of some rare earth elements

Recordings of the isochromat curves of the rare earth elements 64 Gd to 71 Lu have been made by means of a high vacuum spectrometer provided with a bent topaz crystal. The information concerning the density of statesN(E) near the Fermi limit is compared with that deduced from specific heat measurements. The results obtained from the isochromat curves are rather constant, which on account of the atomic configuration in these elements is expected. An observed anomaly in the band structure of Tb metal is discussed. The appearance of this anomaly indicates that a rigid band model is not applicable to some of the actual elements.     

High sensitivity gas spectroscopy of porous, highly scattering solids

We present minimalistic and cost-efficient instrumentation employing tunable diode laser gas spectroscopy for the characterization of porous and highly scattering solids. The sensitivity reaches 3 x 10(-6) (absorption fraction), and the improvement with respect to previous work in this field is a factor of 10. We also provide the first characterization of the interference phenomenon encountered in high-resolution spectroscopy of turbid samples. Revealing that severe optical interference originates from the samples, we discuss important implications for system design. In addition, we introduce tracking coils and sample rotation as new and efficient tools for interference suppression. The great value of the approach is illustrated in an application addressing structural properties of pharmaceutical materials.     

Nonaqueous capillary electrophoresis for analysis of the ethanol consumption biomarker phosphatidylethanol

Nonaqueous CE (NACE) methodology was developed for the separation and determination of phosphatidylethanol (Peth), a new biomarker of ethanol intake. Peth is an abnormal phospholipid formed in cell membranes only in the presence of ethanol, via the transphosphatidylation reaction of phospholipase D. The NACE separation medium consisted of 80 mM ammonium acetate in 50% ACN, 33% 2-propanol, 12% hexane and 5% methanol. A stacking effect was obtained by reducing the concentration of ammonium acetate in the separation medium for all injected samples. The LOD was estimated to 1 microM (5.6 fmol) of Peth with conventional UV detection, equalling 0.4 micromol/L blood. Peth was successfully determined in extracts of human blood samples. Separation of Peth from other blood lipids in the lipid extract sample was performed in 5 min. The method facilitates smaller sample volumes and performs about ten times faster compared to earlier chromatographical methods.     

Aggregation of nanosized colloidal silica in the presence of various alkali cations investigated by the electrospray technique

The slow aggregation process of a concentrated silica dispersion (Bindzil 40/220) in the presence of alkali chlorides (LiCl, NaCl, KCl, RbCl, and CsCl) was investigated by means of mobility measurements. At intervals during the aggregation, particles and aggregates were transferred from the liquid phase to the gas phase via electrospray (ES) and subsequently size selected and counted using a scanning mobility particle sizer (SMPS). This method enables the acquisition of particle and aggregate size distributions with a time resolution of minutes. To our knowledge, this is the first time that the method has been applied to study the process of colloidal aggregation. The obtained results indicate that, independent of the type of counterion, a sufficient dilution of the formed gel will cause the particles to redisperse. Hence, the silica particles are, at least initially, reversibly aggregated. The reversibility of the aggregation indicates additional non-DLVO repulsive steric interactions that are likely due to the presence of a gel layer at the surface. The size of the disintegrating aggregates was monitored as a function of the time after dilution. It was found that the most stable aggregates were formed by the ions that adsorb most strongly on the particle surface. This attractive effect was ascribed to an ion-ion correlation interaction.     

Measuring cellulase activity

An approach is presented for obtaining relative filter paper activities for enzyme preparations having activities below that required for application of the traditional International Union of Pure and Applied Chemistry filter paper assay. The approach involves the utilization of protein stabilizers to retard the time-dependent enzyme inactivation that may occur under traditional filter paper assay conditions. Enzyme stabilization allows extended reaction times and the calculation of relative activities based on the time required for saccharification of 3.6% of the traditional substrate, making results proportional to those obtained in the traditional International Union of Pure and Applied Chemistry assay. The assay is demonstrated using a commercial cellulase preparation along with KCl and bovine serum albumin as protein stabilizers.     

Novel Vinylpyridine Based Cationic MIP Monoliths for Enantiomer Separation in CEC

Cationic vinylpyridine based molecularly imprinted polymer monoliths were, for the first time, applied to enantiomer separation using capillary electrochromatography. In order to map the synthesis conditions under which superporous monoliths are obtained, capillary columns were prepared by an in situ polymerization technique using varying monomer and porogen compositions. Both electrolyte pH and percentage of the organic modifier acetonitrile were found to affect the electrochromatographic behaviour on such columns. An interesting observation is that the electroosmotic flow changed direction from cathodic at high pH to anodic at low pH of the electrolyte, opening up the opportunity to manipulate the flow. This is attributed to the vinylpyridine based MIP becomes protonated and positively charged at low pH, whereas it is uncharged at high pH where instead negatively charged silanol groups drive the electroosmotic flow. Improved enantiomer resolution, as well as increased retention, was observed when the concentration of acetonitrile in the electrolyte decreased, indicating a significant element of hydrophobic effects in the molecular recognition of the imprinted enantiomer. Enantiomer separation of the non-steroidal anti-inflammatory drug ibuprofen was studied and efficiencies as high as 30,000 plates per meter with an asymmetry factor below 4 were obtained for the last eluting imprinted enantiomer. These values are better than that obtained generally using MIP based chromatography.     

The Sorption Behavior of Wood Studied by Means of an Improved Cup Method

In transport models for wood, sorption is an essential parameter. Sorption is the balancing process between the two phases of water present in wood below the fiber saturation point, namely water vapor in the lumens and bound water in the cell walls. To gain better insight into the physical background of transport processes, a special experimental test setup—the improved cup method—is presented. It allows for separation of sorption from other processes. In this test, a diffusion cup contains a thin specimen of wood, with one side facing outwards to a climate chamber and the opposite side facing inwards the cup. In contrast to the common cup method, the herein presented method uses a data logger for relative humidity and temperature placed inside the cup. The use of thin cross-cut specimens allows for explicit separation of the different processes occurring during transient moisture transport. Mass changes were determined and relative humidity inside the cups was measured for eight specimens of Norway spruce with different specimen thicknesses. Relative humidity was increased in three uniform steps in the test chamber from 4.0 up to 76.5%. The results obtained with this special test setup indicate that the sorption process is different than assumed in previous publications. This emphasizes the need of improved modeling approaches.