Combined use of medium mass resolution and desolvation introduction system for accurate plutonium determination in the femtogram range by inductively coupled plasma-sector-field mass spectrometry

Formation of a polyatomic species made of an atom of a heavy element like lead, mercury or iridium, and atoms abundant in plasma (argon, nitrogen, oxygen, and hydrogen) when using an inductively coupled plasma-sector-field mass spectrometer (ICP-SFMS) may lead to false detection of femtograms (fg) of plutonium or bias in the measured concentrations. Mathematical corrections, based on the measurement of heavy element concentrations in the sample solutions and determination of the extents of formation of the polyatomic interferences, are efficient but time-consuming and degrade detection limits. We describe and discuss a new method based on the combination of, on the one hand, medium mass resolution (MR) of the ICP-SFMS to separate plutonium isotopes physically from interfering polyatomic species, and, on the other, use of a desolvation introduction system (DIS) to enhance sensitivity, thus partly compensating for the loss of transmission due to use of a higher resolution. Plutonium peaks are perfectly separated from the major interfering species (PbO₂, HgAr, and IrO₃) with a mass resolution of ~ 4000. The resulting nine-fold transmission loss is partly compensated by a five-fold increase in sensitivity obtained with the DIS and a lower background. The instrumental detection limits for plutonium isotopes, calculated for measurements of pure synthetic solutions, of the new method (known as MR-DIS method) and of the one currently used in the laboratory (LR method), based on a low mass resolution equal to 360, a microconcentric nebulizer and two in-line cooled spray chambers, are roughly equivalent, at around 0.2 fg ml^? 1. Regarding the measurement of real-life samples, the results obtained with both methods agree and the corresponding analytical detection limits for plutonium isotopes ²³⁹Pu, ²⁴⁰Pu and ²⁴¹Pu are of a few fg·ml^? 1 of sample solution, slightly lower with the MR-DIS method than with the current LR method. Although less sensitive than other plutonium ICP-MS measurement methods described in the literature, the main advantage of the MR-DIS method is that it is robust against the risk of false plutonium detection, even in the case of relatively high concentrations of heavy elements like lead, mercury or iridium.     

Compact wideband antenna above a wideband non-uniform artificial magnetic conductor

A compact wideband antenna place above a non-uniform artificial magnetic conductor (AMC) is presented. The antenna is composed of a wideband coplanar waveguide fed antenna, with wideband harmonic suppression characteristic using non-uniform defected ground structure. Besides, a non-uniform wideband AMC is designed. The AMC unit cell is composed of a square patch into which a four arms spiral shape is etched. It exhibits a wider ±90° bandwidth than the spiral unit cell and a smaller size than the square patch unit cell. The antenna is placed above the proposed AMC structure formed by 6 × 5 unit cells. The overall dimensions of the complete structure are 0.7 × 0.6 λ ₀ ² , where λ ₀ is the free-space wavelength at the lowest frequency. It offers a low-profile configuration with a total thickness of λ ₀/14.3, and it is matched between 2.5 and 5.4 GHz (73.5 %). Furthermore, it has a stable main lobe radiation pattern in the E- and H-planes within the operating frequency band. Moreover, compared with the antenna without AMC, the broadside realized gain is significantly increased. A prototype has been realized, and there is a good agreement between simulated and measured results. Furthermore, the proposed structure presents a size reduction of about 34 %, and better radiation characteristics in comparison with the conventional square AMC.     

Triterpenoid Saponins from the Cultivar “Green Elf” of Pittosporum tenuifolium

Four oleanane-type glycosides were isolated from a horticultural cultivar “Green Elf” of the endemic Pittosporum tenuifolium (Pittosporaceae) from New Zealand: three acylated barringtogenol C glycosides from the leaves, with two previously undescribed 3-O-β-d-glucopyranosyl-(1→2)-[α-l-arabinopyranosyl-(1→3)]-β-d-glucuronopyranosyl-21-O-angeloyl-28-O-acetylbarringtogenol C, 3-O-β-d-galactopyranosyl-(1→2)-[α-l-arabinopyranosyl-(1→3)]-β-d-glucuronopyranosyl-21-O-angeloyl-28-O-acetylbarringtogenol C, and the known 3-O-β-d-glucopyranosyl-(1→2)-[α-l-arabinopyranosyl-(1→3)]-β-d-glucuronopyranosyl-21-O-angeloyl-28-O-acetylbarringtogenol C (Eryngioside L). From the roots, the known 3-O-β-d-glucopyranosyl-(1→2)-β-d-galactopyranosyl-(1→2)-β-d-glucuronopyranosyloleanolic acid (Sandrosaponin X) was identified. Their structures were elucidated by spectroscopic methods including 1D- and 2D-NMR experiments and mass spectrometry (ESI-MS). According to their structural similarities with gymnemic acids, the inhibitory activities on the sweet taste TAS1R2/TAS1R3 receptor of an aqueous ethanolic extract of the leaves and roots, a crude saponin mixture, 3-O-β-d-glucopyranosyl-(1→2)-[α-l-arabinopyranosyl-(1→3)]-β-d-glucuronopyranosyl-21-O-angeloyl-28-O-acetylbarringtogenol C, and Eryngioside L were evaluated.     

A new dimension in structural biology: fully fledged high-pressure macromolecular crystallography

The amount of accurate crystallographic data currently available on macromolecular structures at high pressure is extremely limited, mainly due to the lack of appropriate instrumentation and X-ray sources. A technical breakthrough has been achieved with a set-up at the ESRF ID30 beamline equipped with a diamond anvil cell and a large imaging plate, and taking advantage from undulators providing a quasi-plane wave of ultrashort wavelength X-rays. The accessible pressure range is increased by nearly one order of magnitude with respect to beryllium cells. A nearly perfect long-range order is preserved in protein and virus crystals compressed below the denaturation pressure. The quality of diffraction data collected at high pressure can meet usual standards, especially in the case of high symmetry space groups.

An overview of main results and ongoing studies is given, including the 7?kbar structure of hen egg-white lysozyme refined at 1.6?Å resolution and structural investigations of cowpea mosaic virus (CPMV), the first macromolecular assembly investigated at high pressure by single crystal X-ray diffraction. The ordering effect of high pressure on the molecular packing of disordered P23 crystals was highlighted. The 2.8?Å resolution structure of CPMV at 3.3?kbar was fully refined using high completeness data collected on pressure-ordered I23 crystals.     

Steroidal saponins from the fruits of Cestrum ruizteranianum

Seven spirostane and furostane-type glycosides were isolated from the aqueous methanolic extract of the fruits of Cestrum ruizteranianum and characterized mainly by 2D NMR spectroscopy and mass spectrometry. These known saponins belong to the delta5-spirostene and delta5-furostene series and are reported in this species for the first time.     

Resistive high-impedance surfaces (RHIS) as absorbers for oblique incidence electromagnetic waves

This paper presents a lightweight microwave absorber suitable for space applications. The absorber is based on a resistive high-impedance surface (RHIS) optimized to achieve reflection under ?15 dB in the band (2–2.3 GHz) at oblique incidence for transverse electric (TE) and transverse magnetic (TM) polarizations. A first classical isotropic RHIS structure is shown to be limited to angles of incidence up to 40° for TE polarized waves and up to 35° for TM polarized waves. So the objective of this contribution is to present a second solution based on an anisotropic RHIS structure which presents good absorption of incident waves in TE and TM polarizations for larger angles of incidence. An example is presented for an incidence angle of 65°.     

Kinetics and mechanism of racemization of Tic-hydantoins, potent sigma-1 agonists

The configurational stability of seven Tic-hydantoin sigma-1 agonists 1-7 was studied in organic and aqueous media to mimic conditions encountered during either their synthesis or their evaluation as a drug candidate (physico chemical property determination and pharmacological study). This study was performed from the enantiomers directly obtained by asymmetric synthesis (hydantoins 1, 3-7) or after semi-preparative separation of the racemic obtained according to the same asymmetric procedure (thiohydantoin 2), by chiral HPLC. The racemization phenomenon was followed using recently validated chiral HPLC and capillary electrophoresis separation methods using derivatized cellulose and amylose chiral stationary phases (Chiralcel OD-H and Chiralpak AD) and highly sulphated cyclodextrins [highly S-β-CD in the background electrolyte (BGE)], respectively. The kinetic parameters (rate constant, half-life and apparent free energy barriers) of racemization were calculated using a first-order reaction model. The influence of the acid-base content, pH in aqueous medium, concentration of the buffer, and temperature were investigated. The fastest racemization rates were observed under basic conditions. All hydantoins were shown to present the same magnitude of configurational stability, whereas thiohydantoin 2 was characterized by a high chiral instability, especially in ethanolic and aqueous media: its high instability in ethanol explains that a racemic mixture was obtained after asymmetric synthesis; its instantaneous racemization observed from the neutral pH makes the preparation of the enantiomers of 2 not relevant. Finally, the mechanism of racemization was elucidated using nuclear magnetic resonance (NMR): the comparison of the kinetics of the deuteration to the kinetics of the racemization suggests the involvement of a common reaction mechanism of S_E1 type for hydantoin 1, while an S_E2 type reaction seems to be involved for thiohydantoin 2.     

Simulations de l'écoulement turbulent marin avec un modèle de déconvolution

We display a continous equation for the deconvolution process that generalizes the Van Cittert algorithm in the case of oceanic boundary conditions for a given fixed wind. We deduce a LES model for which we have existence and uniqueness of a strong solution. Finally, we display several numerical simulations showing the practical interest of the model. To cite this article: A.-C. Bennis et al., C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Validation of a highly sensitive method for the determination of neonicotinoid insecticides residues in honeybees by liquid chromatography with electrospray tandem mass spectrometry

The validation of a multi-residue method for the determination of five neonicotinoid insecticides (imidacloprid, clothianidin, acetamiprid, thiacloprid and thiamethoxam) in honeybees is described. The method involves the extraction of pesticides using acetonitrile and liquid partitioning with n-hexane. One clean-up is then performed on a florisil cartridge (1?g, 6?mL) and the extract is analysed by liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-ESI-MS/MS). The recovery data were obtained by spiking honeybees samples free of pesticides at two concentration levels of the various neonicotinoids. The recoveries were in the range between 93.3 and 104.0% with relative standard deviation (RSD) less than 20%. The limit of quantification (LOQ) was 0.5?ng?g^?1 (corresponding to 0.05?ng?bee^?1) for all pesticides except for acetamiprid which was 1?ng?g^?1 (corresponding to 0.1?ng?bee^?1).