B. Porsch

High-performance liquid chromatography of sugar mixtures containing xylose and arabinose on primary amino-bonded phases

The extent of the chemical reaction between aldehydic sugars and primary amino groups chemically bonded to the surface of a silica-based sorbent is even larger when silica modified in situ by sorbed diethylenetriamine is employed as the stationary phase. However, the effect of this reaction can be eliminated by employing a suitably buffered mobile phase.

Fractional coefficient of macromolecules in concentrated solution and in the vicinity of the critical solution temperature. Diffusion and sedimentation studies of polystyrene in toluene and trans-decalin

Abstract The concentration dependence of the frictional coefficient ( f ) in concentrated solutions of well-defined polystyrene fractions has been studied both in a good solvent (toluene) and in a solvent where θ conditions and condition in the vicinity of phase separation can be realized ( trans -decalin). f and the self-diffusion coefficient ( D + ) have been calculated from a combination of measured translational diffusion coefficients ( D ) and osmotic pressure data for the systems; polystyrene (M = 390 000) trans- decalin up to 90 kg/m 3 at 20° (θ-conditions), 30° and 40°C; polystyrene (M = 110 000) toluene up to 120 kg/m 3 at 25°C. Sedimentation measurements are also reported. The main results are: (a) over a concentration interval 0–100 kg/m 3 , f shows more than a ten-fold and almost linear increase; (b) in trans -decalin when the temperature is raised from 20° (θ-conditions) to 40°C (good solvent conditions), keeping the concentration constant, f increases only slightly, the increase being somewhat more pronounced at higher concentrations; (c) the concentration dependence of the ratio D D + is considerable under good solvent conditions but becomes gradually less pronounced when θ-conditions are approached; (d) diffusion/osmosis and velocity sedimentation give identical values of f over the entire concentration interval.

Sedimentation in concentrated polystyrene solutions and the observation of an “anomaly” in a good solvent

Abstract Sedimentation coefficients are reported for three polystyrene fractions (molecular weights 1.1 × 10 5 , 3.9 × 10 5 and 1.8 × 10 6 ) in toluene and trans -decalin (θ-conditions) up to high concentrations. The difference between the sedimentation behaviour in good and poor solvents is discussed; an “anomalous” effect was observed in toluene in a concentration region where incipient entanglement is likely.

Influence of the Amount of Bonded Non-Polar Phase and of the Length of Attached Alkyl Chains on Retention Characteristics of Silica-Based Sorbents for Reversed-Phase High Performance Liquid Chromatography

Abstract The retention characteristics of two sets of chemically bonded non-polar silica packings with a high surface concentration of functional groups have been compared in the reversed-phase mode of liquid chromatography: (i) the conventional packings prepared by chemical modification with trimethylsilyl, heptyl, dodecyl and octadecyl groups, and (ii) mixed-phase materials where differences in the amount of organic bonded phase were achieved by bonding octadecyl and trimethylsilyl groups in different proportions. The retention data of two homologous series of solutes show that these two classes of packings are distinctly different; in particular, the capacity factors and selectivities are always higher on the mixed-phase bonded silica packings at the same percentage of carbon.

Rapid isocratic high-performance liquid chromatography of porphyrin esters on aminopropyl-bonded silica

Abstract A simple isocratic procedure for the separation of porphyrin esters according to the number of carboxyl groups using an aminopropyl-bonded silica column and a simple binary eluent is suggested. In this way, problems with the choice of a suitable unmodified silica column for isocratic separation are circumvented; entirely different aminopropyl-bonded silicas of various origins exhibit almost identical behaviour. The influence of end-capping of residual silanols and the chemical substitution of the primary amino group on the separation was studied. To achieve an isocratic separation of porphyrin esters on the bare silica used, the concentration of surface silanol groups must be decreased; suitable concentrations are tailored by means of partial trimethylsilylation. The isocratic separation of porphyrin esters can also be achieved on cyanopropyl-bonded silica. The suggested optimum procedure, using primary amino-bonded silica, gives the highest resolution and allows the baseline separation of porphyrin esters with two to eight carboxyl groups together with their Cu 2+ complexes and synthetic tetraphenylporphyrin as the internal standard.

Chromatographic stability of silica-based aminopropyl-bonded stationary phases

Abstract Causes of frequently observed changes in the properties of columns packed with silica modified with primary amino groups were investigated chromatographically, and it was confirmed that the initial instability of new columns appears to be due to the gradual desorption of the respective silane. Further changes in the chromatographic properties during the operation ensue from deactivation of the surface with impurities capable of reacting with the primary amino group. The main source of these impurities is the mobile phase. Simple prevention can be achieved with a protective column packed with the same sorbent and placed between the pump and the injection valve, ,which allows the column to be used for several months without changes in its chromatographic properties.

System with embedded drug release and nanoparticle degradation sensor showing efficient rifampicin delivery into macrophages

We have developed a biodegradable, biocompatible system for the delivery of the antituberculotic antibiotic rifampicin with a built-in drug release and nanoparticle degradation fluorescence sensor. Polymer nanoparticles based on poly(ethylene oxide) monomethyl ether-block-poly(ε-caprolactone) were noncovalently loaded with rifampicin, a combination that, to best of our knowledge, was not previously described in the literature, which showed significant benefits. The nanoparticles contain a Förster resonance energy transfer (FRET) system that allows real-time assessment of drug release not only in vitro, but also in living macrophages where the mycobacteria typically reside as hard-to-kill intracellular parasites. The fluorophore also enables in situ monitoring of the enzymatic nanoparticle degradation in the macrophages. We show that the nanoparticles are efficiently taken up by macrophages, where they are very quickly associated with the lysosomal compartment. After drug release, the nanoparticles in the cmacrophages are enzymatically degraded, with half-life 88±11 min.

Estimation of polymer polydispersity by diffusion measurements at low concentration

Abstract A method is described for calculating, from measurement of free diffusion by means of the wave front shearing interferometer, three different average diffusion coefficients which can characterize the polydispersity of a sample. The method was tested by measurements on a monodisperse sample, viz. biphenyl. The criteria of polydispersity were determined for two non-fractionated polymers, polyisobutylene and polystyrene. A comparison of calculated and measured number and weight average mol. wts. illustrates the scope of the method.

SILICA BASED AMINOPROPYL-BONDED PHASE TRIMETHYLSILYLATED WITH N-TRIMETHYLSILYLIMIDAZOLE

Abstract N-trimethylsilylimidazole is a suitable agent for the silanization of silica based amino phases, because it reacts selectively with silanol groups. the effect of trimethylsilylation is illustrated chromatographically in anhydrous heptane and in separations of sugar mixtures in the acetonitrile-water mobile phase.

Preparative high-performance liquid chromatographic columns with an intra-column injection system

Abstract Glass and stainless-steel preparative sorbent bed injection columns are described, which can be packed with spherical particles of silica gel and silica-based reversed-phase material, particle size 15 μm, by simple gravity sedimentation. Columns of I.D. 42–44 mm and 250 mm long give symmetrical peaks with loads of 1–2 g; by using sorbent bed injection their lifetime is greatly increased and the use of a compression piston is not needed.