Development of a multi-class method for the quantification of veterinary drug residues in feedingstuffs by liquid chromatography-tandem mass spectrometry

A simple multi-residue method was developed for detecting and quantifying 33 analytes from 13 classes of antibiotics (tetracyclines (3), quinolones (7), penicillins (3), ionophore coccidiostats (7), macrolides (3), sulfonamides (1), quinoxalines (2), phenicols (2), lincosamides (1), diaminopyrimidines (1), polypeptides (1), streptogramins (1) and pleuromutilins (1)) in animal feeds. Extraction and clean-up procedures were optimized with spiked piglet feed. Samples were extracted by ultrasonic-assisted extraction with a mixture of methanol/acetonitrile/McIlvaine buffer at pH 4.6 (37.5/37.5/25, v/v/v) containing 0.3% of EDTA-Na₂, followed by a clean up using a dispersive solid-phase extraction (d-SPE) with PSA (primary secondary amine). Detection of antibiotics was achieved by liquid chromatography-electrospray tandem mass spectrometry (LC–ESI-MS/MS) within 28 min using both positive and negative ESI mode. Average recoveries ranged from 51% (oxytetracycline) to 116% (tilmicosin) with associated relative standard deviations of 7.3% and 9.0% and an overall mean of 87%. Limits of quantification ranged from 3.8 ng g⁻¹ (lincomycin) to 65.0 ng g⁻¹ (bacitracin). Following optimization, the method was further verified for bovine and lamb feedingstuffs; negative matrix effects were evaluated and overcome by a standard addition method.     

The influence of the structure of the double layer on the morphology of the polarographic curves

Conclusions It is emphasized that proper account of the effect allows not only a better understanding of the morphological pecularities of the polarographic curves and a more accurate evaluation of the kinetic constants, but may reciprocally bring useful information about the fine structure of the double layer itself. On a more practical point of view, as only irreversible waves are shifted by variation of ₀, careful adjustement of the supporting electrolyte may improve some simultaneous polarographic determinations. A typical example is the dosage of traces of Zn in Ni, which can be carried successfully in presence of tetraethylammonium ions, which are specifically adsorbed and displace negatively the wave of Nickel only.Enlarged Abstract.     

Un nouveau type d'inégalités pour les martingales discrètes

Summary We prove the following extension of classical Burkholder-Davis-Gundy inequalities: let (X _n ) _nN be a martingale; for p1, in order that and belong to L ^p, it is sufficient that Inf(X ^*, S(X)) belong to L ^p. For «regular» martingales this result holds for p>0.     

Zur sauren Hydrolyse von 1-(N-Methoxymethyl-thiocarbamoyl)-5-methyl-3,3-diphenyl-pyrrolidin-2-imin

The title compound (1) is hydrolysed at pH=0–2 to the new compounds 1-thiocarbamoyl-5-methyl-3.3-diphenylpyrrolidin-2-one (3) and the tetrahydrotriazine derivative (4). These compounds, together with 5-methyl-3.3.-diphenylpyrrolidin-2-imine (5), are the stable end-products of the reaction. The expected 5-methyl-3.3.-diphenyl-1-thiocarbamoyl-pyrrolidin-2-imine (6) is formed either as an intermediate or an end-product according to the conditions of hydrolysis. Its formation is analogous to that of the isomeric 5-methyl-3.3.-diphenyl-2-pyrrolidinylidene-thiourea (9) from 1-(N-methoxymethyl)-3-(5-methyl-3.3.-diphenyl)-2-pyrrolidinylidene)-thiourea (2) by cleavage of the methoxymethyl group.     

Mechanical and swelling equilibrium characterization of high cis-1,4-polyisoprene networks

Equilibrium stress-strain relationships in uniaxial extension for high cis-1,4-polyisoprene (Shell IR 307) networks were obtained by extrapolation of relaxation measurements to infinite time through a Bernstein-Kearsley-Zapas (BKZ) constitutive equation. Three series of networks were investigated, each series being characterized by its polymer precursor molecular weight. The influence of cross-linking density was studied through varying amounts of dicumyl peroxide as cross-linking agent. These results were used to test Flory and Erman's recent molecular theory of networks with constraints on junctions. Swelling equilibrium experiments with benzene and cyclohexane were performed on these networks and were in agreement with the mechanical analysis. The polymer-solvent interaction parameter for the system cis-polyisoprene + cyclohexane was estimated to be 0.31 at 20°C in the range 0 to 0.2 of polymer volume fraction.     

Trace analysis of sulfonylurea herbicides and their metabolites in water using a combination of off-line or on-line solid-phase extraction and liquid chromatography–tandem mass spectrometry

Two alternatives for the rapid simultaneous quantification of six sulfonylurea herbicides and five of their main degradation products in natural water are proposed. For concentration, the compounds were extracted on a polystyrene–divinylbenzene solid phase under pH and elution conditions that suppressed any hydrolysis. The eluates were analysed by liquid chromatography coupled to electrospray tandem mass spectrometry within 20 min. The whole method was validated and shown to give no hydrolysis artefacts. The application of off-line and on-line SPE of sulfonylureas enabled the 0.1 μg L⁻¹ and 1 ng L⁻¹ LOQ levels to be reached, respectively. The on-line SPE–LC–MS–MS method allowed the accurate quantitation of all sulfonylureas and three degradation products at 0.1 μg L⁻¹ or below in natural water, with an average repeatability of 8%.     

Amino wagging and inversion in hydrazine: K′ = 1 levels in the first excited state of the antisymmetric wagging vibration

The infrared absorption spectrum of NH₂NH₂ vapor has been observed in the region 899–1077 cm^?1, where the antisymmetric wagging band (v_a = 1 ← 0) appears, by the use of a Fourier transform spectrometer with a practical resolution of 0.003 cm^?1. In the region 925.0–925.6 cm^?1, the spectrum was also observed with a tunable diode laser, and a component, β, of the ^pQ₂ cluster has been further resolved. Most of the absorption lines assignable to β-^pP₂(J″), γ-^pP₂(J″), β-^pQ₂(J″), γ-^rQ₀(J″), β-^rR₀(J″), and γ-^rR₀(J″), where J″ = 2 ～ 15, have been identified. From these observed transition frequencies, in combination with the ground state energy levels given by microwave spectroscopy, the energy level structure of the K′ = 1 rotational states was determined. From this, the following molecular parameters for the v_a = 1 state were determined: molecular asymmetry, B′-C″ = 0.00017 cm^?1; a parameter q₅ describing an umbrella motion Coriolis interaction (q₅K) about the a axis, q₅ = ?0.0030 cm^?1; its J(J + 1) variation, q_5j = 0.00014 cm^?1; and a parameter describing an umbrella-motion K-type doubling g₅J(J + 1), g₅ = 0.000021 cm^?1.