Temperature‐programmed capillary high‐performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry for analysis of fatty acid methyl esters

A new capillary high‐performance liquid chromatography method with atmospheric pressure chemical ionization mass spectrometry was developed for the analysis of fatty acid methyl esters and long‐chain alcohols. The chromatographic separation was achieved using a Zorbax SB‐C18 HPLC column (0.3 × 150 mm, 3.5 μm) with a mobile phase composed of acetonitrile and formic acid and delivered isocratically at a flow rate of 10 μL/min. The column temperature was programmed simply, using a common column oven. Good reproducibility of the temperature profile and retention times were achieved. The temperature programming during the isocratic high‐performance liquid chromatography run had a similar effect as a solvent gradient; it reduced retention times of later eluting analytes and improved their detection limits. Two atmospheric pressure chemical ionization sources of the mass spectrometry detector were compared: an enclosed conventional ion source and an in‐house made ion source with a glass microchip nebulizer. The enclosed source provided better detectability of saturated fatty acid methyl esters and made it possible to determine the double bond positions using acetonitrile‐related adducts, while the open chip‐based source provided better analytical figures of merit for unsaturated fatty acid methyl esters. Temperature‐programmed capillary high‐performance liquid chromatography is a promising method for analyzing neutral lipids in lipidomics and other applications.     

Constant Current Chronopotentiometric Stripping Analysis of ‘N‐Catalyst’ in Sodium Chloride Solution and Seawater

Catalytic properties and surface activity of nitrogen containing polymeric organic material (N‐POM) were analyzed by constant current chronopotentiometric stripping analysis (CPSA) and alternating current (AC) voltammetry in sodium chloride solution (pH 8) and seawater. CPSA proved to be a suitable method for determination of low concentrations of N‐POM in seawater by measuring its ‘presodium’ catalytic peak H. A protein human serum albumin (HSA) (15% of N) was used as a model compound and the concentration of N‐POM from natural seawater samples was expressed in HSA concentration equivalents. Peak H represents an additional parameter for characterization of natural organic matter.     

Exploring the Loading Capacity of Generation Six to Eight Dendronized Polymers in Aqueous Solution

Aspects of size, structural (im)perfection, inner density, and guest molecule loading capacity of dendronized polymers (DPs) of high generation (6≤g≤8) in aqueous solution are studied using electron paramagnetic resonance spectroscopy on amphiphilic, spin‐labeled guest molecules. The results show that the interior of the charged DPs is strongly polar, especially in comparison to their lower generation (1–4) analogues. This is a direct sign that large amounts of water penetrate the DP surface, reflecting the structural (im)perfections of these high‐generation DPs and much lower segmental densities than theoretically achievable. Images obtained with atomic force microscopy reveal that the high‐generation DPs do not aggregate and give further insights into the structural imperfections. Electron paramagnetic resonance spectroscopic data further show that despite their structural imperfections, these DPs can bind and release large numbers of amphiphilic molecules. It is concluded that attention should be paid to their synthesis, for which a protocol needs to be developed that avoids the relatively large amount of defects generated in the direct conversion of a generation g=4 DP to a generation g=6 DP, which had to be used here.     

Four algorithms to solve symmetric multi-type non-negative matrix tri-factorization problem

Journal of Global Optimization - In this paper, we consider the symmetric multi-type non-negative matrix tri-factorization problem (SNMTF), which attempts to factorize several symmetric...     

Principal/Two-Agent model with internal signal

Central European Journal of Operations Research - Our novel game-theoretic Principal/Two-Agent model ensures that the Principal has a reliable internal signal about the Agents’ invested work...     

Voltammetric Study of Reduction Processes in Rhodium(+3)–Selenium(+4) Acidic Mixtures

Using square‐wave voltammetry and linear scan voltammetry, some reduction processes, that take place on the hanging mercury drop electrode (HMDE) in rhodium(+3)–selenium(+4) mixtures, were studied in highly acidic sulfate, chloride and perchlorate solutions. The special attention was paid to the peak located at ?1.1 V, that reflects catalytic hydrogen evolution on the rhodium islets, and its changes under the influence of added selenium(+4), or selenium(?2) produced at the electrode. It can be concluded that addition of selenite to a dilute rhodium solution has the similar effect as the increase of rhodium(+3) concentration, making the catalytic hydrogen evolution more pronounced, probably by changing the properties of metal clusters on the mercury drop. If so, the effect could be of some practical importance in production of rhodium deposits on other surfaces, too.     

A Double‐Passivation Water‐Based Galvanic Displacement Method for Reproducible Gram‐Scale Production of High‐Performance Platinum‐Alloy Electrocatalysts

Preparation of large quantities of high‐performance supported Pt‐alloy electrocatalysts is crucial for the faster development and implementation of low‐temperature proton exchange membrane fuel cells (PEMFCs). One of the prospective nanofabrication synthesis methods is based on the galvanic displacement (GD) reaction. A facile, highly reproducible, gram scale, water‐based double passivation GD method is now presented for the synthesis of carbon‐supported Pt‐M nanoparticles (M=Cu, Ni, Co). It offers great flexibility over the catalyst design, such as the choice of the sacrificial metal (M), variation of the chemical composition of alloy, variation of total metal loading (Pt+M) on carbon support, or even variation of the carbon support itself. The obtained Pt‐alloy catalysts are several times more active compared to a Pt reference and exhibits better stability during accelerated degradation tests performed at 60 °C.     

MADAM: a parallel exact solver for max-cut based on semidefinite programming and ADMM

Computational Optimization and Applications - We present MADAM, a parallel semidefinite-based exact solver for Max-Cut, a problem of finding the cut with the maximum weight in a given graph. The...