Physical and analytical characteristics of an atmospheric pressure argon–helium radiofrequency capacitively coupled plasma

A very low power radiofrequency capacitively coupled plasma (13.56 MHz, 5–70 W), was generated in our laboratory on a sharp Kanthal tip without any counter electrode, as an intrinsic part of RLC series resonant circuit. Physical characteristics of this plasma obtained in Ar–He mixture, were studied as function of observation height or gas mixture composition. The excitation temperature of Ar (1500–2100 K), He (3000–3500 K) and H (2500–3200 K), the rotational temperature of the OH band (1300–2900 K), the electron temperature (5500–6500 K) and the electron number density (8 · 10¹³–2 · 10¹⁴ cm^− 3) were determined. The evolution of several atomic emission lines or molecular bands was studied in order to investigate the fundamental processes that take place in such plasma. From the point of view of analytical applications it was found that the optimum conditions of excitation (most intense emission lines and lowest detection limits) are met for a 42% He in the gas mixture and an observation height of 1 mm above the electrode. The optimum atomic emission analysis parameters were established for 7 elements (Na, Li, Ca, K, Cd, Zn and Hg) using pneumatically nebulized liquid solutions. It was found that the presence of He in the plasmogenic gas has an enhancing effect on the emission intensities and detection limits.     

Application of pentafluorophenyl hydrazine derivatives to the analysis of nabumetone and testosterone in human plasma by liquid chromatography–atmospheric pressure chemical ionization–tandem mass spectrometry

Two carbonyl compounds, nabumetone and testosterone, were derivatized with pentafluorophenyl hydrazine (PFPH) and analyzed by atmospheric-pressure chemical-ionization mass spectrometry. The PFPH derivatives underwent dissociative electron capture in negative-ion APCI (ECAPCI) and gave intense [M–20]^– ions in the mass spectra. In positive-ion APCI, the PFPH derivatives underwent efficient protonation and gave intense [M+H]⁺ ions in the mass spectra. In CID, the major product ions of the [M–20]^– ions in ECAPCI corresponded to the partial moiety of PFPH. In contrast, the major product ions of [M+H]⁺ corresponded to the partial moiety of the analyte. By using selected reaction monitoring (SRM) detection, low pg of nabumetone (1 pg) and testosterone (7 pg) could be detected in both ECAPCI and positive-ion APCI. In comparison with the detection limits (SRM) of the underivatized analytes, use of the PFPH derivatives resulted in 2500-fold and 35-fold sensitivity enhancements for nabumetone and testosterone, respectively. The PFPH derivatives were applied to the analysis of nabumetone and testosterone in human plasma by both ECAPCI and positive-ion APCI and were found to enable detection of 0.1 ng mL^–1 nabumetone in spiked plasma. For testosterone, endogenous testosterone in female plasma was detected in both ECAPCI and positive-ion APCI.     

Underpinning energetics of lithium bonding and stability in the Li–Pt–Sn system

Within the Li–Pt–Sn system, we examine the electronic structures and Li-binding of LiPtSn₂, Li₂PtSn and Li₃Pt₂Sn₃ with fluorite-related crystal structures. The structures with totally de-intercalated lithium keep the characteristics of the pristine ternary compound with a reduction of the volume. In Li₃Pt₂Sn₃ the binding energies of lithium belonging to three crystallographically inequivalent Wyckoff sites are different and point to distinct activities of de-intercalation concomitant with site-selective bonding magnitudes. The derived potentials are within the range of non-oxide binary and ternary lithium based compounds and indicate the possibility of at least partial delithiation.     

Using the van der Waals broadening of spectral atomic lines to measure the gas temperature of an argon–helium microwave plasma at atmospheric pressure

The applications of plasmas generated with gas mixtures have become increasingly common in different scientific and technological fields. In order to understand the advantages of these discharges, for instance in chemical analysis, it is necessary to know the gas temperature (T_g, kinetic energy of the heavy particles) since it has a great influence on the atomization reactions of the molecules located in the discharge, along with the dependence of the reaction rate on this parameter. The ro-vibrational emission spectra of the molecular species are usually used to measure the gas temperature of a discharge at atmospheric pressure although under some experimental conditions, these are difficult to detect. In such cases, the gas temperature can be determined from the van der Waals broadening of the emitted atomic spectral lines related to this parameter. The method proposed is based on the van der Waals broadening taking into account two perturbers.     

Changes in the composition of the solvation shell of lithium ions in γ-butyrolactone upon addition of 15-crown-5 as studied by quantum chemistry

Quantum chemical modeling of Li⁺ ion transfer from the solvation shell of γ-butyrolactone (GBL) as the solvent to the cavity of 15-crown-5 (15C5) macrocyclic ligand was carried out. Calculations were performed using the PBE nonempirical density functional and an extended basis for the SBK pseudopotential. The solvation energy was included in the framework of the polarizable continuum model. The calculated geometric parameters of GBL and 15C5 molecules are in good agreement with experimental X-ray data. The energies and structures of the Li(GBL) _n ⁺ (n = 1–5) complexes and Li(GBL) _m (15C5)⁺ (m = 0–3) mixed complexes were calculated. The binding energy of the fifth GBL molecule is low; therefore, the Li⁺ ion is mainly surrounded by four GBL molecules. The formation of mixed complexes by consecutive displacement of GBL molecules from the solvation shell of the lithium ion leads to structures with the coordination number 5. The equilibrium constants of these processes were used to determine the dependence of the composition of the solvation complexes on the concentration of 15C5 in the system. The concentrations of the Li(15C5)⁺ and Li(GBL)(15C5)⁺ complexes appeared to be comparable. The revealed structural features of the Li⁺ solvation complexes in the GBL-15C5 system were used to analyze the operating efficiency of lithium power sources.     

Preparation of BaCe0.8Gd0.2O3−δ by the citrate method and its application in the synthesis of ammonia at atmospheric pressure

BaCe_0.8Gd_0.2O_3– is a kind of high-temperature proton conductor. A precursor of BaCe_0.8Gd_0.2O_3– solid electrolyte was synthesized by the citrate method and characterized by thermal analysis (thermogravimetric analysis–differential thermal analysis), X-ray diffraction and scanning electron microscopy. Using the sintered samples as a solid electrolyte and silver–palladium alloy as electrodes, we synthesized ammonia from nitrogen and hydrogen at atmospheric pressure in the solid-state proton-conducting-cell reactor. The rate of evolution of ammonia was up to 3.09×10^–9 mol s^–1 cm^–2.     

Determination of nitrophenolate sodium in aquatic products by HPLC–MS/MS with atmospheric pressure chemical ionization

The paper describes an efficient method for the determination of nitrophenolate sodium in aquatic products by HPLC combined with atmospheric pressure chemical ionization with tandem mass spectrometry (LC–APCI-MS/MS). Analytes were extracted from aquatic products by acetonitrile, the extracts were degreased by alumina and concentrated, the concentrated solution was further purified by Oasis HLB cartridge. Finally, the analytes were separated and detected by LC–APCI-MS/MS in negative ion mode. Excellent linearity with correlation coefficients of more than 0.995 was observed in the concentration range of 2–200 μg/L for p-nitrophenol sodium and 2-methoxy-5-nitrophenolate sodium, and 5–200 μg/L for ο-nitrophenol sodium. Recovery rates of nitrophenolate sodium between 86.1–94.3% were achieved. Limit of quantitation of p-nitrophenol sodium and 2-methoxy-5-nitrophenolate sodium was 2 μg/kg and ο-nitrophenol sodium was 5 μg/kg, with relative standard deviations <10%. This method was employed in the practical analysis of spiked and naturally contaminated aquatic products.     

Preparation and use ofα-bromomono- and-bromobis-difluoromethoxyacetophenones in the synthesis of polymethyleneimidazoles with an angular nitrogen atom

The synthesis of -bromo-4-difluoromethoxy- and -bromo-2,4-bis(difluoromethoxy)acetophenones has been carried out. Conditions have been studied for condensing the latter with cyclic tri- and tetramethylenamidinines and with pyridine-containing derivatives. A series of pyrrolo[1,2-a]imidazole and imidazo[2,1-a]pyridine derivatives containing difluoromethoxy groups has been synthesized.T. G. Shevchenko Chernigov Pedagogical Institute, Chernigov 250038. Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Kiev 252660. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1371–1376, October, 1997.     

Effect of atmospheric pressure on the phase transitions of α,α-trehalose dihydrate DTA study of the dehydration behavior in open systems

The phase transitions of α,α-trehalose dihydrate (T _h) were investigated by either differential thermal analysis (DTA) with an in-house apparatus of variable-pressure type equipped with an open sample holder or commercially available TG (thermal gravimetry)-DTA apparatus for comparison under the same experimental conditions as to the heating rate (2°C min⁻¹), the type of pan (open), and the particle size of T _h (63 μm). The former DTA measurements were carried out under five different total pressures, 101, 75, 61, 48 and 35 kPa, which provided quite helpful information necessary for confirmative assignments of the endothermic peaks due to either melting or dehydration of T _h. The usage of largely different amount of T _h, 126 and 14 mg for the DTA and TG-DTA measurements respectively, led to their different DTA traces, showing that there were largely different extents of the influence by the measured sample surface exposed to the surrounding atmosphere on its dehydration behavior. In addition the high thermal sensitivity achieved with such mass of T _h gave rise to an interesting discovery of an unidentified thermal event at 92°C prior to either melting or dehydration of T _h.     

Thermal stability of the extraction system “TODGA in Isopar M with n-decanol” at above atmospheric pressure

Journal of Thermal Analysis and Calorimetry - The gas evolution dynamics has been studied during thermal oxidation of 0.15 and 0.2&nbsp;mol L?1 solutions of...     

α-Enone by the Reaction of Aldehyde and α-Bromoketone with Tri-n-Butylstibine

α-Enones were readily obtained from the reaction of α-bromoketone with aldehydes mediated by tri-n-butylstibine.     

Determination of Nɛ-homocysteinyl-lysine and γ-glutamylcysteine in plasma by liquid chromatography with UV-detection

Homocysteine (Hcy) is a sulfur-containing nonprotein amino acid, a metabolite of methionine. Mechanisms by which Hcy is involved in the pathogenesis of vascular diseases remain unclear. One of the potential mechanisms underlying harmful effects of Hcy is the protein N-homocysteinylation induced by Hcythiolactone. Proteolytic degradation of N-homocysteinylated protein yields N?-homocysteinyl-lysine, a novel and important component of Hcy metabolism. Here we describe new high-performance liquid chromatography assay for the determination of N?-homocysteinyl-lysine and γ-glutamylcysteine in plasma, based on a derivatization with 2-chloro-1-methyllepidinium tetrafluoroborate and UV detection. Baseline separation was achieved on an analytical column from Phenomenex (Kinetex C18, 100 × 4.6 mm, 2.6 μm) using gradient elution, with a mobile phase consisting 0.1 M trichloroacetic acid (pH 2.3) — acetonitrile. The quantification limits for N?-homocysteinyl-lysine and γ-glutamylcysteine in plasma were 0.1 and 0.2 μM, respectively. Other main endogenous thiols can also be measured during the same analytical run. The proposed method was applied for the analysis of 15 plasma samples for total form of N?-homocysteinyl-lysine and γ-glutamylcysteine.     

Synthesis of 20α-Methylsteroids with an Izoxaline Ring in the Side Chain

1,3-Dipolar addition of acetonitrile oxide to 20-methyl-22-hydroxy-23-ene-steroids and acetoxy derivatives thereof was investigated. The reaction is stereoselective and affords as the main product 5'S-epimer resulting from syn-addition both in the case of allyl alcohol and its ether.     

Reductive α-alkylation of ketones with aldehydes at atmospheric pressure of carbon monoxide: the effect of fluoride activation in ruthenium catalysis

Fluoride additive to [(p-cymene)RuCl₂]₂, a readily available ruthenium catalyst, allows one to achieve milder conditions for the reductive alkylation of aldehydes with ketones using carbon monoxide as a reducing agent. The procedure is suitable for the broad substrate scope, and a probable explanation for the fluoride role was provided.     

Synthesis of transparent silica aerogels with low density and better hydrophobicity by controlled sol–gel route and subsequent atmospheric pressure drying

In the present paper, attempts have been made to produce transparent silica aerogels with low density and better hydrophobicity by controlled sol–gel route and subsequent atmospheric pressure drying. The hydrogels were prepared by hydrolysis and polycondensation of sodium silicate (Na₂SiO₃) in the presence of acetic acid catalyzed water followed by several washing steps with water, methanol and hexane, respectively. The surface modification of the wet gel was carried out using a mixture of hexamethyldisilazane (HMDS) in hexane. Since, the sol–gel chemistry provides a straightforward method to control the physical and optical properties of the aerogels, the influence of various sol–gel parameters viz. gel washing time, molar ratios of CH₃COOH/Na₂SiO₃ and HMDS/Na₂SiO₃ and silylation period on the physical and optical properties of the aerogels have been investigated. The aerogels have been characterized by bulk density, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric and Differential Thermal Analysis (TG-DTA), Atomic Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM) studies and Contact angle measurements.     

Chemical behaviors of tritium produced by the 6Li(n, α)T reaction in lithium oxide

The chemical forms of tritium released from neutron-irradiated crystalline powders of Li₂O, LiOH and Li₂CO₃ have been investigated over the temperature range of 100–600°C with radio-gas chromatography and mass spectrometry. When the target materials are heated to 600°C under vacuum after the irradiation, more than 96% of tritium is released as hydrogen oxide, HTO, and collected in the cold trap cooled at −72°C. Tritium is also released in forms such as HT (and T₂), CH₃T and C_nH_2n+x − T (n = 2, x = 0, 1, 2), although their percentages are rather low. The release of HTO is interpreted by supposing that recoil tritium produced by the ⁶Li(n, α)T reaction is first stabilized as LiOT in the solids and then released by the reaction LiOT·LiOH(c)→Li₂O(c)+HTO(g) at a temperature between 250 and 400°C.     

A cooperative participation of the amido group in the organocatalytic construction of all-carbon quaternary stereocenters by Michael addition with β-ketoamides

The secondary amido group of α-substituted β-ketoamides plays a crucial role in the control of the reactivity and spatial arrangement (selectivity) in the organocatalyzed Michael addition to unsaturated carbonyls. This results in an unprecedented activation mode of substrates through H-bonding interactions allowing the construction of enantiomerically enriched functionalized all-carbon quaternary centers and spiroaminals of high synthetic potential.     

7α-alkylation, 7,7-bisalkylation,and reduction of the 20-oxo group of poststerone in reactions with alkyl halides in lithium–ammonia solution

Reactions of poststerone with methyl iodide, allyl bromide, and propargyl bromide in lithium–ammonia solution resulted in its completely stereoselective 7α-alkylation accompanied by reduction of the 20-oxo group with formation of equimolar amounts of 20R- and 20S-hydroxy derivatives. The reaction of poststerone with excess allyl bromide afforded 7,7-bis-allyl 20R- and 20S-alcohols at a ratio of 3: 1. The reduction of the 20-oxo group in the alkylation of poststerone with excess propargyl bromide led to the formation of an equimolar mixture of Δ⁸⁽¹⁴⁾- and Δ⁸⁽⁹⁾-isomers with exclusive S configuration of C²⁰.