Laser induced excitation transfer in helium glow discharge

Some experimental results on the temporal decay of the fluorescence induced by a resonant laser pulse excitation focused onto a helium gas discharge are presented. In particular, excitation transfer between singlet-singlet and singlet- triplet sub-levels has been studied when 2¹ S → 3¹ P and 2¹ P → 4¹ D transitions of He I are optically pumped.     

Automatic gravimetric apparatus for recording the adsorption isotherms of gases or vapours onto solids

The assembly described was built with the aim of obtaining high resolution and precision, together with automaticity. It was designed around a symmetrical commercial vacuum microbalance (Setaram), its main features being the following:(1) Controlled “residual” vacuum during outgassing of the sample.(2) Two possible procedures for the introduction of the adsorbate: either a conventional — but automated — point by point procedure (with discontinuous introduction of gas or vapour) or a continuous procedure, specially suited for high resolution work.(3) Measurement of pressure (0–1 atm) by a silica Bourdon gague (Texas Instruments) of 10^?5 accuracy.(4) Direct recording of the isotherms on a XY recorder.(5) Constant level (± 0.5 mm) cryogenic bath (liquid nitrogen or argon) of low consumption (4 liters per 15 hours).(6) Liquid thermostat for adsorption temperatures between ? 30 and + 100°C.(7) Temperature control (up to 50°C) of the whole assembly (manifolds, balance, gauges) allowing to handle condensable vapours.Several examples are given, illustrating the versatility and resolution of the systems. For instance, it allowed to detect, for the first time, a distinct substep at the top of the nitrogen/graphite and argon/graphite isotherms at 77 K. This is now explained by a sudden localization or “freezing” of the monolayer near its completion.     

Therapeutic Fc‐fusion proteins: Current analytical strategies

Fc‐Fusion proteins represent a successful class of biopharmaceutical products, with already 13 drugs approved in the European Union and United States as well as three biosimilar versions of etanercept. Fc‐Fusion products combine tailored pharmacological properties of biological ligands, together with multiple functions of the fragment crystallizable domain of immunoglobulins. There is a great diversity in terms of possible biological ligands, including the extracellular domains of natural receptors, functionally active peptides, recombinant enzymes, and genetically engineered binding constructs acting as cytokine traps. Due to their highly diverse structures, the analytical characterization of Fc‐Fusion proteins is far more complex than that of monoclonal antibodies and requires the use and development of additional product‐specific methods over conventional generic/platform methods. This can be explained, for example, by the presence of numerous sialic acids, leading to high diversity in terms of isoelectric points and complex glycosylation profiles including multiple N‐ and O‐linked glycosylation sites. In this review, we highlight the wide range of analytical strategies used to fully characterize Fc‐fusion proteins. We also present case studies on the structural assessment of all commercially available Fc‐fusion proteins, based on the features and critical quality attributes of their ligand‐binding domains.     

Fast and sensitive supercritical fluid chromatography – tandem mass spectrometry multi-class screening method for the determination of doping agents in urine

This study shows the possibility offered by modern ultra-high performance supercritical fluid chromatography combined with tandem mass spectrometry in doping control analysis. A high throughput screening method was developed for 100 substances belonging to the challenging classes of anabolic agents, hormones and metabolic modulators, synthetic cannabinoids and glucocorticoids, which should be detected at low concentrations in urine. To selectively extract these doping agents from urine, a supported liquid extraction procedure was implemented in a 48-well plate format. At the tested concentration levels ranging from 0.5 to 5 ng/mL, the recoveries were better than 70% for 48–68% of the compounds and higher than 50% for 83–87% of the tested substances. Due to the numerous interferences related to isomers of steroids and ions produced by the loss of water in the electrospray source, the choice of SFC separation conditions was very challenging. After careful optimization, a Diol stationary phase was employed. The total analysis time for the screening assay was only 8 min, and interferences as well as susceptibility to matrix effect (ME) were minimized. With the developed method, about 70% of the compounds had relative ME within the range ±20%, at a concentration of 1 and 5 ng/mL. Finally, limits of detection achieved with the above-described strategy including 5-fold preconcentration were below 0.1 ng/mL for the majority of the tested compounds. Therefore, LODs were systematically better than the minimum required performance levels established by the World anti-doping agency, except for very few metabolites.     

Photodissociation Rate Constants of New Light Sensitive Alkoxyamines

The photochemical properties of two new photocleavable alkoxyamines bearing a benzophenone‐derived chromophore were studied by electron spin resonance (ESR). The C O bond cleavage has been demonstrated and the photolysis rate constants (k_d) determined over a large range of light intensity through the monitoring of the nitroxide concentration in aerated conditions. The obtained kinetic data highlight for the first time the linear dependence of k_d on the light intensity for alkoxyamines: this should be a driving factor for nitroxide mediated radical photopolymerization (NMP²).

     

High throughput qualitative analysis of polyphenols in tea samples by ultra-high pressure liquid chromatography coupled to UV and mass spectrometry detectors

The analysis of polyphenols in tea extracts is important due to their potential health benefits. Therefore, efficient and high throughput analytical methods have been developed for the separation of seven predominant polyphenols, also known as catechin derivatives, present in tea extracts. Columns packed with sub-2-μm particles operating at elevated pressure (UHPLC strategy) were selected to improve chromatographic performance. The potential of UHPLC–UV was demonstrated with baseline resolution of all standard catechins in only 30 s using a 50-mm column packed with 1.7-μm particles. When dealing with real samples such as tea extracts, however, longer columns of up to 150 mm in length were employed to enhance the separation of catechin derivatives and other constituents within the tea samples while maintaining an acceptable analysis time. Two strategies based on 2-D experiments were proposed to clearly identify catechins. Firstly, a liquid–liquid extraction procedure was added prior to the UHPLC–UV analysis to decrease the complexity of the sample. Secondly, UHPLC was coupled to ESI-MS/MS to attain sufficient sensitivity and selectivity between catechin derivatives and other constituents of tea extract. These two strategies were found extremely promising as a clear discrimination of catechins from the matrix could be attained.     

Enhanced method performances for conventional and chiral CE-ESI/MS analyses in plasma

Due to its high efficiency, selectivity, and sensitivity, CE-ESI/MS has evolved as an efficient technique for the drugs and metabolites analysis in biological matrices. However, a sample preparation is mandatory prior to CE-ESI/MS analysis. To achieve fast and simplified sample preparation of plasma samples, protein precipitation (PP) and liquid-liquid extraction (LLE) were used with two injection techniques: hydrodynamic (HD) and electrokinetic (EK) injection. CE-ESI/MS analyses of pharmaceutical compounds and amphetamine derivatives were developed. Detection limits of 1 ppm were reached with PP and HD injection whereas 1 ppb was detected when samples were prepared with LLE and injected by EK. Same experiments were performed for stereoselective determinations in partial-filling mode and detection limits achieved were equivalent to conventional analysis (0.5 ppb per enantiomer). When complex matrices are analyzed, MS signal suppression or enhancement effects are generally not reproducible and could compromise results with ESI. Therefore, matrix effect was investigated in CE-ESI/MS with a commercially available coaxial sheath-liquid ESI interface used as postcapillary infusion system to determine MS signal alterations. Matrix effects were differentially evidenced according to the selected sample preparation. With PP, signal suppression was observed out of the analyses migration window, while for LLE no relevant matrix effect occurred in all experiments.