MSPD procedure for determining buprofezin,tetradifon, vinclozolin,and bifenthrin residues in propolis by gas chromatography–mass spectrometry

A simple and effective extraction method based on matrix solid-phase dispersion (MSPD) was developed to determine bifenthrin, buprofezin, tetradifon, and vinclozolin in propolis using gas chromatography–mass spectrometry in selected ion monitoring mode (GC–MS, SIM). Different method conditions were evaluated, for example type of solid phase (C₁₈, alumina, silica, and Florisil), the amount of solid phase and eluent (n-hexane, dichloromethane, dichloromethane–n-hexane (8:2 and 1:1, v/v) and dichloromethane–ethyl acetate (9:1, 8:2 and 7:3, v/v)). The best results were obtained using 0.5 g propolis, 1.0 g silica as dispersant sorbent, 1.0 g Florisil as clean-up sorbent, and dichloromethane–ethyl acetate (9:1, v/v) as eluting solvent. The method was validated by analysis of propolis samples fortified at different concentration levels (0.25 to 1.0 mg kg⁻¹). Average recoveries (four replicates) ranged from 67% to 175% with relative standard deviation between 5.6% and 12.1%. Detection and quantification limits ranged from 0.05 to 0.10 mg kg⁻¹ and 0.15 to 0.25 mg kg⁻¹ propolis, respectively.     

Synthesis of 2-diphenylphosphinoyl-3,5-(diaryl)-3,4-dihydro-2H-thiopyrans by the reaction of a bis[(diphenylphosphinoyl)methyl]sulfide with chalcones

The NaH-promoted tandem Michael addition/intramolecular Horner-Wittig reaction of bis(diphenylphosphinoylmethyl)sulfide with chalcones afforded 3,4-dihydro-2H-thiopyrans 3a-l in 78-88% yield.     

UV laser-induced desorption mechanism analyzed through two-layer alkali halide samples

Time of flight-mass spectrometry (TOF-MS) is used to analyze positive and negative desorbed ions generated by UV laser ablation of several alkali (X) halide (Y) salts. Most of the observed desorbed cluster ions have the structure (XY)(n)X(+) or (XY)(n)Y(-). Their desorption yields decrease as exp(-kn), where k approximately 2 for both series, suggesting that the neutral component (XY)(n) plays the dominant role in the desorption process. Mass spectrum measurements were performed for compound samples in which two salts (out of CsI, RbI, KBr, KCl and KI) are homogeneously mixed or disposed in two superposed layers. The detection of small new ion species and large cluster ions of the original salts supports the scenario that the uppermost layers are completely atomized while deep layers are emitted colder and fragmented: It is proposed that ns-pulsed laser induced desorption of ionic salts occurs via two sequential mechanisms: (1) ejection of cations and anions in the hot plume, followed by recombination into new cluster ions and (2) ejection of relatively cold preformed species originated from deep layers or from periphery of the irradiated region.     

On finite groups with automorphisms whose fixed points are Engel

The main result of the paper is the following theorem. Let q be a prime, n a positive integer, and A an elementary abelian group of order q². Suppose that A acts coprimely on a finite group G and assume that for each \({a \in A^{\#}}\) every element of C_G(a) is n-Engel in G. Then the group G is k-Engel for some \({\{n,q\}}\)-bounded number k.     

Influence of Molar Mass and Concentration on the Thermogelation of Methylcelluloses

In this study, thermogelation of methylcelluloses is investigated in relation to the molar mass and concentration in aqueous medium. A large hysteresis between heating and cooling ramps was observed whatever the conditions. The heating process in particular was studied to analyze the two steps of gelation using rheometry. At low temperature, in the sol state, viscosity depends on the concentration and molar mass. Over 30°C a gel-like behavior was observed including two steps (the second step is a strong gel with phase separation) having storage moduli that are nearly independent of polymer molar mass but are directly related to polymer concentration.     

Assessment of pharmacokinetic interaction between piracetam and l‐carnitine in healthy subjects

A rapid, sensitive and specific method for quantifying piracetam in human plasma using Piracetam d‐8 as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by one‐step precipitation of protein using an acetonitrile (100%). The extracts were analyzed by high‐performance liquid chromatography coupled with electrospray tandem mass spectrometry (HPLC‐MS/MS). The method had a chromatographic run time of 3.8 min and a linear calibration curve over the range 0.5–50 µg/mL (r > 0.99). This LC‐MS‐MS procedure was used to assess the bioavailability of two piracetam formulations: piracetam + l‐carnitine (Piracar®; 270/330 mg tablet) and piracetam (Nootropil®; 800 mg tablet) in healthy volunteers of both sexes. The geometric means with corresponding 90% confidence interval (CI) for test/reference percentage ratios were 88.49% (90% CI = 81.19 – 96.46) for peak concentration/dose and 102.55% (90% CI = 100.62 – 104.51) for AUC_inf/dose. The limit of quantitation of 0.5 µg/mL is well suited for pharmacokinetic studies in healthy volunteers. It was concluded that piracetam (Piracar®; 270/330 mg tablet) has a bioavailability equivalent to the piracetam (Nootropil®; 800 mg tablet) formulation with regard to both the rate and the extent of absorption. Copyright © 2015 John Wiley & Sons, Ltd.     

Positive and negative ionic desorption from condensed formic acid photoexcited around the O 1s-edge: Relevance to cometary and planetary surfaces

Photon stimulated ion desorption (PSID) studies have been performed in condensed formic acid using oxygen 1s-edge synchrotron radiation from the Brazilian synchrotron light source (LNLS), operating in a single-bunch mode. Ion formation was discussed in terms of the Auger stimulated ion desorption (ASID) and X-ray induced electron stimulated desorption (XESD) mechanisms. It is found that O 1s(C-OH) → π*(CO) and O 1s(CO) → 3s/σ*(HCO) transitions favored the production of C⁺, CH⁺, O⁺, O⁻ and H⁻ ions. The hydroxyl anion has not been observed while the hydroxyl cation showed low intensity or was absent. Some anion formation routes from dissociative reactions are suggested taking into account the positive ion yields.