Sorption of methanol,dimethyl carbonate,methyl acetate,and acetone vapors in CTA and PTMSP: General findings from the GAB Analysis

Sorption of vapors of four organic compounds in two glassy polymers, cellulose triacetate (CTA) and poly[(trimethylsilyl)propyne] (PTMSP), has been reported and analyzed in terms of Guggenheim‐Anderson‐De Boer (GAB) model. These two structurally and physicochemically different glassy polymers both independently showed that one sorption site was formed by about three monomeric units. This finding held true for vapors of all characterized compounds; that is, for methanol, for its derivatives dimethyl carbonate and methyl acetate, and for acetone. The “rule of three” might thus also be applicable to other sorbates and glassy polymers. Further, an original modification of the GAB model for the sorption of alcohols in PTMSP was derived and successfully tested. Overall, the analyses of the sorption isotherms, heats of sorption and diffusion coefficients supported the view that the sorption of vapors in glassy polymers has adsorptive nature. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 561–569     

Reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry

The mechanisms of the reduction of Cu(II) in matrix-assisted laser desorption/ionization mass spectrometry (MALDI) are studied. In MALDI mass spectra, ions cationized by copper mostly contain Cu(I) even if Cu(II) salts are added to the sample. It was found that Cu(II) was reduced to Cu(I) by gas-phase charge exchange with matrix molecules, which is a thermodynamically favorable process. Under some conditions, large amounts of free electrons are present in the plume. Cu(II) can be even more efficiently reduced to Cu(I) by free electron capture in the gas phase. The matrices studied in this work are nicotinic acid, dithranol, and 2,5-dihydroxybenzoic acid.     

Vapour permeation and sorption in fluoropolymer gel membrane based on ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide

The emissions of hydrocarbons from fossil fuels into atmosphere entail both an economic loss and an environmental pollution. Membrane separations can be used for vapour recovery and/or vapour removal from the permanent gas stream, given that the appropriate membrane is identified. A neat poly(vinylidene fluoride-co-hexafluoropropylene) membrane is impermeable to both the representatives of aliphatic hydrocarbons and branched hydrocarbons, namely hexane and isooctane, whereas the permeation flux is enhanced by the presence of 80 mass % of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide in the membrane, as detailed in this work. The permeabilities of hydrocarbon vapours were determined from the binary mixture containing hydrocarbon and nitrogen to simulate the real input of an air stream containing a condensable hydrocarbon. The diffusion coefficient determined from sorption measurements was higher for hexane, as would be expected for a smaller molecule, whereas both the sorption isotherms and permeabilities of the hydrocarbons studied were found to be almost identical. It is possible that the sorption effect predominates in the transport mechanism for VOCs/N₂ separations.     

A weight-function approach for determining watershed initial conditions for combustion waves

In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed.     

Cardiac markers: a clear cause for point-of-care testing

Point-of-care testing (POCT) in patients with ischemic heart disease is driven by the time-critical need for fast, specific, and accurate results to initiate therapy instantly. According to current guidelines, the results of the cardiac marker testing should be available to the physician within 30 min (“vein-to-brain” time) to initiate therapy within 60–90 min (“door-to-needle” time) after the patient has arrived at the emergency room or intensive care unit. This article reviews the current efforts to meet this goal (1) by implementing POCT of established biochemical markers such as cardiac troponins, creatine kinase MB, and myoglobin, in accelerated diagnosis and management workflow schemes, (2) by improving current POCT methods to obtain more accurate, more specific, and even faster tests through the integration of optical and electrochemical sensor technology, and (3) by identifying new markers for the very early and sensitive detection of myocardial ischemia and necrosis. Furthermore, the specific requirements for cardiac POCT in regard to analytical performance, comparability, and diagnostic sensitivity/specificity are discussed. For the future, the integration of new immunooptical and electrochemical chip technology might speed up diagnosis even further. However, every new development will have to meet the stringent method validation criteria set for corresponding central laboratory testing.     

Quantized ν = 5/2 state in a two-subband quantum hall system

The evolution of the fractional quantum Hall state at filling 5/2 is studied in density tunable two-dimensional electron systems formed in wide wells in which it is possible to induce a transition from single- to two-subband occupancy. In 80 and 60 nm wells, the quantum Hall state at 5/2 filling of the lowest subband is observed even when the second subband is occupied. In a 50 nm well, the 5/2 state vanishes upon second subband population. We attribute this distinct behavior to the width dependence of the capacitive energy for intersubband charge transfer and of the overlap of the subband probability densities.     

On-line atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry

A new technique is presented for the coupling of atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) mass spectrometry with liquid delivery systems. Mass measurements of polymers and peptides are demonstrated using a co-dissolved matrix, e.g. alpha-cyano-4-hydroxycinnamic acid (HCCA). Improvements in terms of sensitivity are achieved by optimizing the shape und control of the exit capillary and by using a laser (355 nm) at a 1 kHz repetition rate. Two calibration experiments promise a good applicability of the presented coupling method for quantitative measurements. The limit of detection achieved so far is 500 nM for peptides in methanol solution containing 25 mM HCCA.     

Critical comparison of ICP-OES, XRF and fluorine volatilization-FTIR spectrometry for the reliable determination of the silicon main constituent in ceramic materials

For the optimization of preparation processes for ceramic powders and compacts by pyrolysis of inorganic polymers, the intermediate and final products have to be monitored by in-situ analysis (in its original place) for main, subsidiary and trace components. In the determination of silicon in Si-N-C- based ceramic samples by ICP-OES after pressurized decomposition at temperatures between 220°–250°C too low concentrations of Si were found. Completely independent analytical procedures were applied to trace systematic errors, i.e. XRF after decomposition of the sample in a metaborate/boric acid melt and FTIR-spectrometry after reaction of the sample with fluorine. The low recoveries of Si were found to be due to losses, which amount up to 25% depending on the temperature and time applied for the pressurized decomposition. With the latter two procedures Si can be determined in the %-range with a relative standard deviation of 0.4% and 0.2%, respectively.     

Sorption and diffusion of organic vapors in amorphous Teflon AF2400

Vapor sorption in amorphous Teflon AF2400 of various organic solutes was studied in a wide range of activity at 25 °C by means of the gravimetric technique. The sorption isotherms of hexane, toluene, and chloroform were shown to be concave to the pressure axis and are consistent with the dual mode sorption model (DMS). The parameters of the DMS model k_D and b reveal a linear correlation with squared critical temperature of solutes T. The third model parameter, the Langmuir sorption capacity C′_H decreases when the size of solutes (critical volume) increases. Sorption isotherms of methanol and ethanol were shown to be convex to the pressure axis and are consistent with cluster formation in this strongly hydrophobic polymer. Concentration‐dependent diffusion coefficients D were determined using a linear implicit difference scheme in analysis of sorption kinetics. It was shown that D values increase exponentially with concentration for all the solutes, except alcohols for which exponential reduction of D(C) was observed. The partitioning of the thermodynamic and mobility contributions in D indicated that the reduction of D values of alcohols is consistent with clustering phenomena in AF2400. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 832–844, 2006