Highly sensitive and selective separation of intact parathyroid hormone and variants by sheathless CE‐ESI‐MS/MS

Parathyroid hormone (PTH) is a common clinical marker whose quantification relies on immunoassays, giving variable results as batch, brand, or target epitope changes. Sheathless CE‐ESI‐MS, combining CE resolution power and low‐flow ESI sensitivity, was applied to the analysis of PTH in its native conformation in the presence of related forms. Fused silica and neutral‐coated capillaries were investigated, as well as preconcentration methods such as transient isotachophoresis, field‐amplified sample injection (FASI), and electrokinetic supercharging (EKS). The method for the separation of PTH and its variants was first developed using fused‐silica capillary with UV detection. An acidic BGE was used to separate 1–84 PTH (full length), 7–84 PTH, and 1–34 PTH. Acetonitrile was added to the BGE to reduce peptide adsorption onto the capillary wall and transient isotachophoresis was used as analyte preconcentration method. The method was then transferred to a sheathless CE‐ESI‐MS instrument. When using a fused silica capillary, CE‐MS was limited to μg/mL levels. The use of a neutral coating combined with FASI or EKS allowed a significant increase in sensitivity. Under these conditions, 1–84 PTH, 7–84 PTH, and 1–34 PTH were detected at concentrations in the low ng/mL (FASI) or pg/mL (EKS) range.     

Volatile compounds profiling by using proton transfer reaction‐time of flight‐mass spectrometry (PTR‐ToF‐MS). The case study of dark chocolates organoleptic differences

Direct‐injection mass spectrometry (DIMS) techniques have evolved into powerful methods to analyse volatile organic compounds (VOCs) without the need of chromatographic separation. Combined to chemometrics, they have been used in many domains to solve sample categorization issues based on volatilome determination. In this paper, different DIMS methods that have largely outperformed conventional electronic noses (e‐noses) in classification tasks are briefly reviewed, with an emphasis on food‐related applications. A particular attention is paid to proton transfer reaction mass spectrometry (PTR‐MS), and many results obtained using the powerful PTR‐time of flight‐MS (PTR‐ToF‐MS) instrument are reviewed. Data analysis and feature selection issues are also summarized and discussed. As a case study, a challenging problem of classification of dark chocolates that has been previously assessed by sensory evaluation in four distinct categories is presented. The VOC profiles of a set of 206 chocolate samples classified in the four sensory categories were analysed by PTR‐ToF‐MS. A supervised multivariate data analysis based on partial least squares regression‐discriminant analysis allowed the construction of a classification model that showed excellent prediction capability: 97% of a test set of 62 samples were correctly predicted in the sensory categories. Tentative identification of ions aided characterisation of chocolate classes. Variable selection using dedicated methods pinpointed some volatile compounds important for the discrimination of the chocolates. Among them, the CovSel method was used for the first time on PTR‐MS data resulting in a selection of 10 features that allowed a good prediction to be achieved. Finally, challenges and future needs in the field are discussed.     

'On-off-on' fluorescent indicators of pH windows based on three separated components

'On-off-on' fluorescent indicators for pH windows are obtained with ternary systems in which the three separated components are Cu2+, a tetraaza ligand and the fluorophore Coumarin 343: protonation of Coumarin 343, its coordination to Cu2+ and its displacement from Cu2+ by OH- give an inverse bell-shaped variation of emission with pH.     

Modification of MCM-48-, SBA-15-, MCF-, and MSU-type mesoporous silicas with transition metal oxides using the molecular designed dispersion method

Four various mesoporous silicas (MCM-48, SBA-15, MCF, and MSU) were modified by the molecular designed dispersion method using Fe(acac)3, Cr(acac)3, and Cu(acac)2 complexes. The deposition was performed at the same concentration of the metal acetylacetonate (acac) complex in a toluene solution. All as-synthesized samples were investigated by diffuse reflectance infrared Fourier transform spectroscopy, Fourier transform infrared photoacoustic spectroscopy, and thermogravimetric analysis. The calcined materials were studied with respect to their textural properties (Brunauer-Emmett-Teller adsorption isotherm) and chemical composition (electron microprobe analysis). It allowed elucidation of the mechanism of interaction between the acac complex and the silanol groups. For the MCM-48, SBA-15, and MCF materials, the formation of hydrogen bonding was found for the chromium- and copper-modified samples, whereas the Fe-containing materials showed the ligand exchange mechanism. The strong interaction of the MSU support and the different acetylacetonate complexes, resulting in a loss of at least one acac ligand, was observed. The mesoporous silicas modified with transition metal oxides were studied by UV-vis-DR spectroscopy. The different metal dispersions were found for the samples containing various transition metal oxides.     

Approximation of the Distribution of the Supremum of a Centered Random Walk. Application to the Local Score

Let (X _n ) _{n 0} be a real random walk starting at 0, with centered increments bounded by a constant K. The main result of this study is: |P(S _n n x)–P( sup_{0 u 1} B _u x)| C(n,K) n/n, where x 0, ² is the variance of the increments, S _n is the supremum at time n of the random walk, (B _u ,u 0) is a standard linear Brownian motion and C(n,K) is an explicit constant. We also prove that in the previous inequality S _n can be replaced by the local score and sup₀ u 1 B _u by sup₀ u 1|B _u |.     

Short-time dynamics through conical intersections in macrosystems

The short-time dynamics through a conical intersection of a macrosystem with a vast number of nuclear degrees of freedom (modes) is investigated. For convenience, the macrosystem is decomposed into a system carrying a few modes and a "bath." By transforming the bath modes to new ones, it is shown that only three effective bath modes contribute to the conical intersection. They govern--together with the system's modes--the short-time dynamics of the macrosystem. The remaining bath modes do not directly couple the electronic states and become relevant at longer times. An extensive numerical example is presented.     

Electrochemical properties and structures of surface-fluorinated graphite for the lithium ion secondary battery

Surface modification of graphite powder has been performed by elemental fluorine and radiofrequency (rf) plasma fluorination. Both methods give rise to an enlargement of the surface areas of graphite samples and a change of the pore volume distribution. The capacities of surface-fluorinated graphite samples are higher than those of original samples and even more than the theoretical capacity of graphite, 372 mAh g⁻¹, without any reduction of the first colombic efficiencies. The increments of the capacities are ∼5, 10, and 15% for graphite samples with average particle diameters of 7, 25 and 40 μm, respectively.     

Co-tunneling of the charge through a 2-D electron island

A double barrier Single Electron Transistor is realized in two dimensions by confining the 2-D electron gas of a GaAs/GaAlAs heterojunction to a small island by means of Schottky gates. Two gates provide adjustable tunnel barriers and a central gate controls the electron number in the island. The island has small single-particle energy level spacing and forms a metallic island. Periodic conductance oscillations characteristic of Coulomb blockade are observed when the central gate voltage is varied. The ability to vary the tunnel conductance allows us to study the basic physics of the Coulomb blockade: our results show that the quantum charge fluctuation mechanism which limits the tunneling blockade at low temperature is of second order in tunnel barrier transparencies in agreement with the charge Macroscopic Quantum Tunneling (q-MQT) or co-tunneling model.     

Facile and selective metalation of 7-dehydro-cholesterol (pro-vitamin D3)

Subsequent treatment of 7-dehydrocholesterol with trimethylsilylmethylpotassium in tetrahydrofuran, dry ice, mineral acid and diazomethane gives a regioisomerically pure, homoconjugated ester as a diastereomeric mixture, the minor component of which turns out to be thermodynamically more stable than a conjugated isomer.     

Plasmons in icosahedral quasicrystals: An EELS investigation

We present the results of an electron energy loss spectroscopy (EELS) investigation of the icosahedral quasicrystals i-Al-Cu-Fe, i-Al-Pd-Mn and i-Al-Pd-Re. The spectra of the three systems studied are very similar. Their main contribution comes from a broad plasmon like peak, which can be interpreted as an “s-p" electron plasmon damped by “d" electron interband transitions. We show that it is similar to those found in other simple crystalline aluminum-transition metal alloys, so that no specificity related to the quasicrystalline order of the alloys dominates. Received 3 November 1998 and Received in final form 16 July 1999