Flow and transport in electrochromatography

von Ivo Nischan

Controlled ultraviolet (UV) photoinitiated fabrication of monolithic porous layer open tubular (monoPLOT) capillary columns for chromatographic applications

An automated column fabrication technique that is based on a ultraviolet (UV) light-emitting diode (LED) array oven, and provides precisely controlled "in-capillary" ultraviolet (UV) initiated polymerization at 365 nm, is presented for the production of open tubular monolithic porous polymer layer capillary (monoPLOT) columns of varying length, inner diameter (ID), and porous layer thickness. The developed approach allows the preparation of columns of varying length, because of an automated capillary delivery approach, with precisely controlled and uniform layer thickness and monolith morphology, from controlled UV power and exposure time. The relationships between direct exposure times, intensity, and layer thickness were determined, as were the effects of capillary delivery rate (indirect exposure rate), and multiple exposures on the layer thickness and axial distribution. Layer thickness measurements were taken by scanning electron microscopy (SEM), with the longitudinal homogeneity of the stationary phase confirmed using scanning capacitively coupled contactless conductivity detection (sC(4)D). The new automated UV polymerization technique presented in this work allows the fabrication of monoPLOT columns with a very high column-to-column production reproducibility, displaying a longitudinal phase thickness variation within ±0.8% RSD (relative standard deviation)

Analysis of Macromolecular Systems as Enabler for Energy and Life Science Applications

Ideas concerning the conceptual existence of macromolecular and colloidal systems found their inception at the beginning of the last century. The experimental technology developed to discover and characterize those systems can be associated with seminal pioneers laying the foundations for microscopic, hydrodynamic, and light scattering approaches. In this perspective, we focus our attention on the origins of the discovery and characterization of macromolecular and colloidal systems with selected examples from the beginnings to the present. This perspective attempts to directly interconnect the design of new macromolecular as well as colloidal systems and the simultaneous development of using advanced characterization techniques for design verification. While not claiming a complete coverage of the entire field of modern polymer science, our selected examples concern the field of life science and the recently and rapidly developing area of energy materials. Macromolecular and colloidal systems represent a complex and extensive field of research. This perspective gives a brief historical overview of the major historical achievements in the experimental assessment of such systems. Based on this line of enabled discoveries, the authors perspective on the enabling role of analysis in energy and life science is described with example

Determination of omega end functionalities in tailored poly 2 alkyl 2 oxazoline s by liquid chromatography and mass spectrometry

The in depth analytical characterization of polymers, in particular regarding intended biomedical applications, is becoming increasingly important to elucidate their structure property relationships. Specifically, end group analysis of e.g. polymers featuring a stealth effect towards the immune system is of particular importance because of their use in coupling reactions to bioactive compounds. Herein, we established a liquid chromatography LC protocol to analyse bicyclo[6.1.0]nonyne functionalized poly 2 alkyl 2 oxazoline s POx s as promising functional polymers that can be applied in strain promoted click reactions. This work involved the synthesis of poly 2 methyl 2 oxazoline PMeOx and poly 2 ethyl 2 oxazoline PEtOx by living cationic ring opening polymerization CROP with different molar masses ranging from 2 up to 17.5 kDa and, to our knowledge, the first liquid chromatographic analysis of PMeOx. The developed analytical protocol enables the quantitative determination of post polymerization reaction sequences with respect to the conversion of the omega end groups. All synthesized polymers were straightforwardly analysed on a C18 derivatized silica monolithic column under reversed phase chromatographic conditions with a binary mobile phase gradient comprising a mixture of acetonitrile and water. Subsequent mass spectrometry of collected elution fractions enabled the confirmation of the desired omega end group functionalities and the identification of synthetic by product

Tailor made polymer tracers reveal the role of clay minerals on colloidal transport in carbonate media

Hypothesis Host rock weathering and incipient pedogenesis result in the exposition of minerals, e.g., clay minerals in sedimentary limestones. Once exposed, these minerals provide the surfaces for fluid solid interactions that control the fate of dissolved or suspended compounds such as organic matter and colloids. However, the functional and compositional diversity of organic matter and colloids limits the assessment of reactivity and availability of clay mineral interfaces. Such assessment demands a mobile compound with strong affinity to clay surfaces that is alien to the subsurface. Experiment We approached this challenge by using poly ethylene glycol PEG as interfacial tracer in limestone weathering experiments. Findings PEG adsorption and transport was dependent on the availability of clay mineral surfaces and carbonate dissolution dynamics. In addition, PEG adsorption featured adsorption desorption hysteresis which retained PEG mass on clay mineral surfaces. This resulted in different PEG transport for experiments conducted consecutively in the same porous medium. As such, PEG transport was reconstructed with a continuum scale model parametrized by a Langmuir type isotherm including hysteresis. Thus, we quantified the influence of exposed clay mineral surfaces on the transport of organic colloids in carbonate media. This renders PEG a suitable model colloid tracer for the assessment of clay surface exposition in porous medi

Hyperbranched TEMPO based polymers as catholytes for redox flow battery applications

Application of redox active polymers RAPs in redox flow batteries RFBs can potentially reduce the stack cost through substitution of costly ion exchange membranes by cheap size exclusion membranes. However, intermolecular interactions of polymer molecules, i.e., entanglements, particularly in concentrated solutions, result in relatively high electrolyte viscosities. Furthermore, the large size and limited mobility of polymers lead to slow diffusion and more sluggish heterogeneous electron transfer rates compared to quickly diffusing small molecules. Although a number of RAPs with varying electrolyte viscosities have been reported in the literature, the relation between the RAP structure and the hydrodynamic properties has not been thoroughly investigated. Herein, hyperbranched 2,2,6,6 tetramethylpiperidinyloxyl TEMPO based polymers intended for application as low viscosity catholytes for RFBs are presented and the influence of the structure and the molar mass distribution on the hydrodynamic properties is investigated. A new synthesis approach for TEMPO based polymers is established based on step growth polymerization of a TEMPO containing monomer using an aza Michael addition followed by a postpolymerization modification to improve solubility in aqueous solutions. The compact structure of hyperbranched polymers was demonstrated using size exclusion chromatography SEC with viscometric detection and the optimum molar mass was found based on the results of viscometric and crossover investigations. The resulting RAP revealed a viscosity of around 21 mPas at a concentration corresponding to around 1 M TEMPO containing units, according to the calculated mass of the repeating unit, showing potential for high capacity polymer based catholytes for RFBs. Nevertheless, possible partial deactivation of TEMPO units lowered the active TEMPO concentration of the hyperbranched RAPs. A faster diffusion and higher charge transfer rate were observed for the hyperbranched polymer compared to the previously reported linear polymers. However, in RFB tests, a poor performance was observed, which is attributed to the side reactions of the oxidized TEMPO moieties. Finally, pathways for overcoming the main remaining challenges, i.e., high loss of material during dialysis as an indication of being prone to crossover, the partial deactivation of TEMPO moieties, and the subsequent side reactions under battery conditions, are suggeste

PEtOxylated polyesteramide nanoparticles for the delivery of anti inflammatory drugs

Poly ester amide s PEAs consisting of L valine Val , glycolic acid G , and L isoleucine Ile , i.e., PValG and PIleG, and various poly 2 ethyl 2 oxazoline block poly ester amide copolymers PEtOx b PEA were investigated for their suitability as particle based delivery systems for the anti inflammatory drugs BRP 187 and BRP201. A small scale, high throughput formulation approach was utilized to evaluate the nanoparticle properties in dependence of the composition of mixtures of PEA homo and copolymers. Atomistic molecular dynamics simulations of PValG and PIleG with the active ingredients indicated thermodynamic compatibility of the PEAs with the drugs. Drug encapsulation studies confirmed the formation of stable formulations, and the enzymatic degradation of the nanoparticles was also demonstrated. The nanoparticles exhibited no cytotoxicity and were able to efficiently deliver the active pharmaceutical ingredients, i.e., BRP 187 and BRP 201 into macrophages and HEK293 cells. All nanoparticle systems displayed anti inflammatory effectiveness as they were able to suppress cellular 5 lipoxygenase activity. The most promising effects were obtained with the block copolymerbased PEtOx b PEA nanoparticles, which revealed an enhanced performance compared to the control PLGA nanoparticle