New fluorinated thermoplastic elastomers. I. The synthesis and thermal characteristics of α,ω‐dihydrosilane hybrid fluorinated polysiloxane precursors

The synthesis of new α,ω‐dihydrosilane hybrid fluorinated polysiloxanes is described via the polycondensation between a diallyl perfluorinated compound and tetramethyldisiloxane. Control over the size of the oligomers is possible when the reaction is performed in two steps. The length of the polysiloxane chains influences the glass‐transition temperature and the thermal stability of the fluorinated oligomers: the higher the length is, the higher the glass‐transition temperature and the thermal stability are. The synthesized compounds have been characterized with ¹H, ¹⁹F, and ²⁹Si NMR spectroscopy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4485–4492, 2002     

Batch-injection stripping voltammetry (tube-less flow-injection analysis) of trace metals with on-line sample pretreatment

The most essential limitation of batch-injection analysis (BIA) methodology compared to other flow methods (CFA, FIA, SIA) is the lack of possibility of on-line sample processing in the measuring system. Some procedures of on-line sample pretreatment in BIA are possible by changing the plastic tip of the automatic micropipette used for sample injection into a flow-through reactor, e.g. by packing it with a bed of a solid sorbent. This concept is employed in the voltammetric stripping determinations of trace metals using a bed of commercial chelating resin Chelex-100. It was found that, besides the electrochemical preconcentration of analytes in the form of amalgams on the surface of mercury thin film electrodes, an approximately 10-fold additional preconcentration can be achieved on the packed sorbent bed by using different volumes of aspirated sample solution and eluent. This procedure allows also efficient elimination of some matrix effects.     

Comparison between Gibbs free energy minimization and mass action law for a multitemperature plasma with application to nitrogen

This paper gives all the necessary physical equations to determine the composition and the thermodynamic properties in a multitemperature plasma utilizing two different methods: the first method is based on Gibbs free energy minimization and the second is based on the resolution of the mass action law. The lowering terms of the ionization potential and thermodynamic properties are given for a multitemperature plasma using the Debye-Hückel approximation. Numerical application is made to a nitrogen plasma.     

Determination of persistent organohalogenated pollutants in human hair reference material (BCR 397): an interlaboratory study

A human powdered hair material (BCR 397) was tested for its content in persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs). Using different methods, three laboratories (two from Canada and one from Belgium) analysed a powdered hair sample to evaluate some methodologies and to obtain consensus values for selected POPs. Measured values for all PCB congeners and p,p-DDE were within a relative standard deviation (RSD) of 15%. These first results contribute to the accuracy and precision for POPs quantification in hair and render test results more comparable among different laboratories.     

Evaluation of nanopores as candidates for electronic analyte detection

In an effort to increase throughput and decrease the cost of electrophoretic separation of DNA and proteins, various groups are developing highly parallel, miniaturized separation devices based on capillaries etched into silicon, glass or plastic substrates. To date, these miniaturized devices have relied on optical detectors, thus placing a lower limit on instrument size, and complicating the incorporation of an entire DNA analyzer instrument on a chip. To address this limitation, we are evaluating nanopores as candidate Coulter counters for purely electronic detection of analytes in miniaturized electrophoresis and similar separation devices. To establish feasibility of this detection scheme, we have investigated the detection sensitivity of a nanopore sensor through experiments with the alpha-hemolysin (alpha-HL) ion channel, and through a Monte Carlo (MC) model of polymer capture rate with a cylindrical nanopore under an applied voltage. Experimental and model results are extrapolated to predict the capture rate of synthetic pores operating at higher voltages than presently achievable with protein pores.     

Ab initio conformational analysis of 1,3-propanedithiol

By carrying out Hartree-Fock full, symmetry unconstrained geometry optimizations on the 25 symmetrically unique staggered conformers, using the 4-31+G^* basis set it was found that, on the Hartree-Fock level, gTTg and gTTg′ are the lowest energy rotamers in 1,3-propanedithiol. We also found a number of clear conformational trends. Intramolecular hydrogen bonding was found to be of minor importance. The introduction of electron correlation yields a stabilization of the rotamers with one or two gauche SCCC arrangements relative to those with less gauche SCCC arrangements. Consistent with this, we find that on the MP2 level the most stable conformers are gGGg′ and gGGg.     

A Statistical Mechanical View of the Determination of the Composition of Multi‐Temperature Plasmas

It is important that plasma composition is calculated in a manner consistent with statistical mechanics, particularly since the Boltzmann equation is the basis from which transport coefficients and the fluiddynamic equations are derived. It is shown from statistical mechanical considerations based on the Boltzmann equation and the Htheorem that it is (i) not possible for a plasma to have more than one temperature in equilibrium in the absence of external forces and gradients, and (ii) not possible to draw conclusions about the change in entropy of a plasma in the presence of external forces and gradients. Derivations of the twotemperature Saha equation, and more generally calculations of the composition of a multitemperature plasma, that are based on entropy maximization are therefore invalid. A thermodynamic derivation of the composition of a multitemperature plasma that is consistent with the statistical mechanical results is presented. The derivation shows that the equilibrium composition of a plasma can be correctly calculated by minimization of the internal or free energy.     

Determination of aliphatic aldehydes in aqueous solution by chemiluminescence measurements

The determination of aliphatic aldehydes (5 × 10^-6 — 2.5 × 10^-4 mol) in aqueous solution was achieved by inhibition of the luminol chemiluminescence induced by hydrogen peroxide in the presence of potassium hexacyanoferrate(III).