Preparation and evaluation of monolithic poly(N-vinylcarbazole-co-1,4-divinylbenzene) capillary columns for the separation of small molecules

Short-term polymerization or the so-called low-conversion polymerization was applied for the preparation of N-vinylcarbazole (NVC) and 1,4-divinylbenzene (DVB) monolithic capillary columns. The synthesis was carried out by thermally initiated free radical copolymerization under the influence of inert micro- (toluene) and macroporogen (1-decanol) and α,α′-azoisobutyronitrile (AIBN) as radical initiator. The morphological and porous properties were studied by scanning electron microscopy (SEM), nitrogen adsorption, and mercury intrusion porosimetry (MIP). The copolymerization process was studied by monomer conversion measurements. This approach led to increased porosity and specific surface area. A specific surface area above 400 m²/g of the monolith and a distinct bimodal pore size distribution were obtained. The chromatographic performance was determined in terms of theoretical plate heights and number of theoretical plates. The lowest plate height value was found to be 3.9 μm (corresponding to ≈256,000 plates per meter) applying methylparaben utilizing an 80 mm?×?0.2 mm i.d. monolithic capillary. The developed NVC/DVB monolithic supports showed high separation efficiency towards small molecules, which was exemplified applying reversed-phase (RP) separation of alkylbenzenes, beta-blockers, flavanoids, parabens, and phenones. The loading capacity was analyzed for isocratic separation of seven alkylbenzenes and was found to be up to 77 ng total mass of alkylbenzenes. Furthermore, a long-term stability test of 1,000 consecutive runs was performed and resulted in a maximum variance of 0.97, 0.85, and 0.16 % RSD for resolution, peak width at half height, and retention times, respectively. The material was proven to have a high permeability of 1.11E?14 m², applying water as a mobile phase.     

Harmonic and intermodulation distortions and noise associated with two-tone modulation of high-speed semiconductor lasers

We present results of modeling and simulation of the harmonic and intermodulation distortions as well as the intensity noise of high-speed semiconductor lasers under two-tone modulation. Multiple quantum-well lasers are considered, which are characterized by large differential gain and a modulation bandwidth of about 25GHz. The study is based on the rate equation model of semiconductor lasers excited by injection current with two sinusoidal tones separated by a radio frequency. The modulated laser signal is modeled in both the time and frequency domains. The time domain characteristics include the fluctuating waveform, while the frequency domain characteristics include the frequency spectrum of the relative intensity noise (RIN), carrier-to-noise ratio, modulation response, harmonic distortion, and the second- and third-order intermodulation distortions (IMD2 and IMD3). The analysis is performed for three frequencies of 5, 15, and 24 GHz, which are, respectively, lower, comparable, and higher than the laser relaxation frequency. The range of the modulation depth covers the regimes of small and large-signal modulation. We show that both RIN and IMD3 of two-modulated laser are minimum when the modulation frequency is 5GHz, and maximum when the modulation frequency is 24 GHz. The second-order harmonic distortion, IMD2, and IMD3 values are larger in the vicinity of relaxation oscillations and increase with the modulation index, especially under large-signal modulation.     

Synthesis of magnetite nanoparticles coated with polyvinyl alcohol for hyperthermia application

Journal of Thermal Analysis and Calorimetry - One of the main challenges in hyperthermia treatment is how to improve the heating performance of nanoparticles with high specific loss power (SLP). To...     

Rate of convergence for ergodic continuous Markov processes: Lyapunov versus Poincaré

We study the relationship between two classical approaches for quantitative ergodic properties: the first one based on Lyapunov type controls and popularized by Meyn and Tweedie, the second one based on functional inequalities (of Poincaré type). We show that they can be linked through new inequalities (Lyapunov-Poincaré inequalities). Explicit examples for diffusion processes are studied, improving some results in the literature. The example of the kinetic Fokker-Planck equation recently studied by Hérau and Nier, Helffer and Nier, and Villani is in particular discussed in the final section.     

Mode-competition noise associated with microwave modulation of multimode semiconductor lasers

We analyze the mode-competition (MC) phenomenon and the associated noise in multimode semiconductor lasers at microwave modulation. The study is based on the multimode rate-equation model, which takes into account the mechanisms of modal gain suppression. The MC is evaluated by the correlation coefficients between oscillating modes in the laser cavity. We show that an increase in the modulation depth changes the mode coupling from anticorrelation to positive correlation and then to complete coupling, which corresponds to emission of periodic pulses. The frequency spectra of relative intensity noise (RIN) exhibit sharp peaks at the modulation frequency and higher harmonics. The increase in the modulation depth is associated with suppression of the total and modal RIN under high-frequency modulation and with noise enhancement under low-frequency modulation.     

Théorèmes de section et de projection pour les processus a deux indices

Sans résumé     

Quantitative detection of phosphoproteins by combination of two-dimensional difference gel electrophoresis and phosphospecific fluorescent staining

Here we combine a standard two-dimensional difference gel electrophoresis (DIGE) protocol with subsequent post-staining of gels with phosphospecific fluorescent Pro-Q Diamond dye. The combination of these two methods for fluorescence detection of proteins allows quantitative detection of phosphoproteins in 2-DE-gels. We established this protocol within a functional proteomics experiment. Mammary epithelial cells (EpH4) were stimulated in culture by epidermal growth factor (EGF), endosomal fractions prepared after subcellular fractionation and phosphorylated proteins successfully detected on endosomes. For instance, Endo A cytokeratin, known as phosphoprotein and differentiation marker inducible by MAPK signaling, was identified by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). With this protocol, all steps of combined proteome and phosphoproteome profiling experiments are significantly simplified and accelerated, taking full advantage of both methods in terms of specificity, sensitivity and accuracy of quantification.     

Analysis of carbohydrates using different quaternized polystyrene-divinylbenzene particles and pulsed amperometric detection

Summary This paper reports on the use of a polymer-based, strong anion-exchange stationary phase for rapid, selective and sensitive analysis of physiological important mono-, di- and oligosaccharides by high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) under alkaline conditions. The adsorbent was obtained by direct nitration of 3 and 5 μm, spherical non-porous highly cross-linked, styrene-divinylbenzene copolymer (PS-DVB) beads, followed by reduction of superficially introduced nitro groups with nascent hydrogen and quaternization of the resultant amino groups with iodomethane. Extended exposure to high pressure and strong alkaline conditions did not have any untoward effect on mechanical stability and chromatographic performance. A comparison of the 3 and 5 μm beads showed, that the synthesized 3 μm highly cross-linked PS-DVB particles are the preferred phases for the separation of monosaccharides and the 5 μm particles are preferable for the separation of oligosaccharides. To demonstrate the suitability for the analysis of complex samples, the optimized and validated system was used for the determination of glucose, fructose and sucrose in apple juice and other soft drinks such as Coca Cola. Finally, analysis within a few minutes without sample pretreatment down to a lower limit of detection of 0.174–0.504 μg mL⁻¹ at a linearity with R²>0.994 and a repooducibility higher than 98% further confirmed the efficiency of these polymeric sorbents.     

Monolithic poly(glycidyl methacrylate-co-divinylbenzene) capillary columns functionalized to strong anion exchangers for nucleotide and oligonucleotide separation

In the present work, poly(glycidyl methacrylate-co-divinylbenzene) monoliths were synthesized and further derivatized to obtain strong anion exchange supports. Capillary monoliths (65 x 0.2 mm id) were prepared in situ by copolymerization of glycidyl methacrylate and divinylbenzene, employing 1-decanol and tetrahydrofuran as porogens. The free epoxy groups were derivatized in a two step synthesis to obtain quaternary ammonium functionalities. On testing the pressure stability of the synthesized monolith, a highly linear dependence between flow rate and pressure drop was obtained, indicating the high stability of the material even at high flow rates. The morphology of the copolymer was investigated by scanning electron microscopy. Mercury intrusion porosimetry showed a narrow pore size distribution, having a maximum at 439 nm. On recording a van Deemter plot the number of theoretical plates per meter was found to be 59324. The produced strong anion exchange monoliths turned out to be highly suitable for the separation of nucleotides and oligonucleotides.     

Uranium(VI) recovery from acidic leach liquor using manganese oxide coated zeolite (MOCZ) modified with amine

Journal of Radioanalytical and Nuclear Chemistry - Manganese oxide coated zeolite modified with trioctyl amine (MOCZ/TOA) was tested for adsorption of uranium. Different experiments were performed...