Synthesis and Application of Histidine-Modified Poly(Glycidyl Methacrylate/Ethylene Glycol Dimethacrylate) Sorbent for Isolation of Caffeine from Black and Green Tea Samples

This work presents the synthesis of a polymeric mixed-mode solid-phase extraction (SPE) sorbent for clean-up and isolation of caffeine from black and green tea samples. The material was synthesized by a simple thermally initiated copolymerization of glycidyl methacrylate and ethylene glycol dimethacrylate. Further functionalization was executed with histidine (HIS). Functional groups were investigated by attenuated total-reflection infrared spectroscopy. Furthermore, nitrogen sorption porosimetry was executed and revealed surface areas of 90 m² g^??1. Adsorption capacities for caffeine were compared between functionalized and non-modified polymers and showed maximum capacities of 3.01 and 4.82 mg g^??1 polymer, respectively. Time adsorption profiles revealed an equilibrium adsorption after 15 min. The proposed polymer was used for SPE of black and green tea extracts and showed excellent clean-up efficiency for isolation of caffeine with recoveries ranging from 89 to 93%. When compared to commercially available Oasis HLB, the HIS-functionalized polymer demonstrated a distinctly better performance for clean-up. Finally, the proposed method was validated regarding international (ICH) guidelines and regulations.     

Enrichment of low-abundant serum proteins by albumin/immunoglobulin G immunoaffinity depletion under partly denaturing conditions

We present a simple protocol for affinity depletion to remove the two most abundant serum proteins, albumin and immunoglobulin G (IgG). Under native conditions, albumin/IgG were efficiently removed and several proteins were enriched as shown by two-dimensional electrophoresis (2-DE). Besides that, partly denaturing conditions were established by adding 5 or 20% acetonitrile (ACN) in order to disrupt the binding of low-molecular-weight (LMW) proteins to the carrier proteins albumin/IgG. 2-DE results showed that the total number of detected LMW proteins increased under denaturing conditions when compared to native conditions. Interestingly, the presence of 5% ACN in serum revealed better enrichment of LMW proteins when compared to 20% ACN condition. Seven randomly distributed spots in albumin/IgG depleted serum samples under 5% ACN condition were picked from the 2-DE gels and identified by mass spectrometry (MS). The intensity of five LMW protein spots increased under denaturing conditions when compared to native conditions. Three of the seven identified spots (serum amyloid P, vitamin D-binding protein, and transthyretin) belong to a group of relatively low-abundant proteins, which make up only 1% of all serum proteins. The method presented here improves the resolution of the serum proteome by increasing the number of visualized spots on 2-D gels and allowing the detection and MS identification of LMW proteins and proteins of lower abundance.     

Effects of nanoconfinement on the morphology and reactivity of organic materials

When organic materials are placed in environments which physically confine the materials at the nanometre scale, interfacial effects and confinement-induced loss of entropy can significantly alter materials' properties such as the glass transition temperature as well as the nanoscale morphology as compared to a "free" system. In block copolymers, nanoconfinement leads to a range of unusual self-organized nanoscale morphologies. In this article, attempts to induce nanoconfinement effects in new polymer systems as well as at interfaces will be highlighted and some possible future implications for organic synthesis and biology will be discussed.     

Eine analytische Brennstoffzelle als Alkoholsensor

An analytical fuel cell for the quantitative determination of alcohols is described. As an example of application its use as selective gas-chromatographic detector is demonstrated. The cell contains a symmetrical bipolar Pt/Pt gas diffusion electrode with an acid electrolyte which is surrounded by air on both sides. By this arrangement the reaction was not influenced by air because the rate of chemisorption of ethanol was much greater than that of oxygen. The polarization of the measuring electrode as a criterion of sensitivity was about 3 mV/μg ethanol.     

Fast, noninvasive and simultaneous near-infrared spectroscopic characterisation of physicochemical stationary phases' properties: from silica particles towards monoliths

The design of novel stationary phases is a permanent demanding challenge in chromatographic separation science to enable analysis with enhanced selectivity, specificity and speed. Therefore, the characterisation of chemical and physical properties is next to calculation of chromatographic parameters essential. Conventionally, chemical parameters including surface coverage are determined by burning combustion or frontal analysis, physical parameters including particle size, pore size, pore volume and surface area are determined by SEM, mercury intrusion porosimetry (MIP) and Brunauer-Emmett-Teller (BET). All these methods are time consuming, invasive and require besides special equipment some special trained laboratory staff. Therefore, we introduced near-infrared spectroscopy (NIRS) as a noninvasive, easy-to-handle technology with wavenumber ranging from 4000 to 10,000 cm(-1) enabling analysis within only a few seconds at higher precision than the conventional methods. Investigated materials comprise porous and nonporous silica gel, carbon-based nanomaterials (fullerenes), polymer beads and monoliths. Different carriers themselves and their kind of derivatisations (RP, normal-phase, ion-exchanger, IMAC (immobilised metal affinity chromatography), affinity) can be determined by applying principal component analysis (PCA) of recorded spectra. Partial least square regression (PLSR) enables the determination of particle size, pore size, pore volume, porosity, total porosity and surface area with one single measurement. For the optimised design of well-defined polymer beads and monoliths, real-time in situ monitoring to control, e. g. particle and pore sizes as well as monomer content during the polymerisation process, can be extremely helpful. In this article, the advantages of this fast, noninvasive high-throughput NIRS methods are summarised, discussed in detail and different applications of the individual characterised materials are shown.     

On the alkali instability of phenoxazine dyes as adsorbates of chemically modified electrodes

The alkali instability of phenoxazine dyes was investigated with respect to their application as catalysts for anodic NADH oxidation. Spectrophotometric measurements were used in aqueous solutions at different pH values together with cyclovoltammograms of the dyes adsorbed on a graphite electrode. It is shown that the reason for desactivation in the case of Meldola Blue is a cation-pseudobase equilibrium followed by a ring-opening tautomerism. The open-ring isomer, an unstable o,p′-quinoneanile dye, could be isolated as a dark blue precipitate. Also a by-product (“dimethyl”-Nile Red V) was identified. In the case of phenoxazine dyes substituted with an amino or acylamino group in p-position to the heterocyclic nitrogen, the reason for desactivation of the electrodes is the known reversible formation of a quinone diimine as an anhydrobase.     

Progress in capillary electrophoresis coupled to matrix-assisted laser desorption/ionization - time of flight mass spectrometry

In this review the most important techniques developed to hyphenate CE to MALDI-TOF-MS are summarized. The principles of the different interfaces and ways to solve the hyphenation problem are explained and discussed in detail. The most important applications especially in the proteomic field are reviewed, and the advantages of CE-MALDI-TOF-MS for the analysis of these compounds compared to other techniques such as ESI-MS are exhaustingly discussed from a critical point of view. CE coupled to MALDI-TOF-MS has started to overpass traditionally used CE-coupling techniques, especially CE-ESI-MS, offering the possibility to analyze samples of interest even weeks after CE analysis and using multiplexing systems for high-sample throughput.     

Capillary electrochromatography of biologically relevant flavonoids

Flavonoids were separated utilizing CEC technique. Baseline separation of biologically relevant flavonoids was obtained using a 100 microm ID fused-silica capillary filled with 3 microm Silica-C18 material and an optimized mobile phase comprising of 20 mM Tris-HCl (pH 6.5), ACN and water at a ratio of 10/40/50 v/v/v. Separations were carried out at 25 kV and a column temperature of 25 degrees C. The influence of relevant parameters for the CEC separation, such as buffer concentration, pH, separation voltage, and ACN concentration, was investigated and optimized. Dependencies of the electroendoosmotic flow (EOF) on these parameters and effects on the resolution of the analytes were studied. During analyses the solvents used for dissolving the samples turned out to have significant effects on the separation of flavonoids. The optimized system was then successfully used for the separation of the flavonoids epicatechin, myricetin, quercetin, naringenin, and hesperetin. CEC turned out to be a useful complementary tool for the economic analysis of flavonoids in addition to common HPLC, muHPLC, and CE methodologies. This method can be used for real applications in phytomics.