Controlling Floquet states on ultrashort time scales.

The advent of ultrafast laser science offers the unique opportunity to combine Floquet engineering with extreme time resolution, further pushing the optical control of matter into the petahertz domain. However, what is the shortest driving pulse for which Floquet states can be realised remains an unsolved matter, thus limiting the application of Floquet theory to pulses composed by many optical cycles. Here we ionized Ne atoms with few-femtosecond pulses of selected time duration and show that a Floquet state can be observed already with a driving field that lasts for only 10 cycles. For shorter pulses, down to 2 cycles, the finite lifetime of the driven state can still be explained using an analytical model based on Floquet theory. By demonstrating that the amplitude and number of Floquet-like sidebands in the photoelectron spectrum can be controlled not only with the driving laser pulse intensity and frequency, but also by its duration, our results add a new lever to the toolbox of Floquet engineering.

A systematic study of the valence electronic structure of cyclo(Gly-Phe), cyclo(Trp-Tyr) and cyclo(Trp-Trp) dipeptides in the gas phase.

The electronic energy levels of cyclo(glycine-phenylalanine), cyclo(tryptophan-tyrosine) and cyclo(tryptophan-tryptophan) dipeptides are investigated with a joint experimental and theoretical approach. Experimentally, valence photoelectron spectra in the gas phase are measured using VUV radiation. Theoretically, we first obtain low-energy conformers through an automated conformer-rotamer ensemble sampling scheme based on tight-binding simulations. Then, different first principles computational schemes are considered to simulate the spectra: Hartree-Fock (HF), density functional theory (DFT) within the B3LYP approximation, the quasi-particle GW correction, and the quantum-chemistry CCSD method. Theory allows assignment of the main features of the spectra. A discussion on the role of electronic correlation is provided, by comparing computationally cheaper DFT scheme (and GW) results with the accurate CCSD method.

[Determination of benzimidazoles residue markers in chicken tissue by high performance liquid chromatography].

A method was developed for the simultaneous determination of 11 benzimildazoles residue markers in chicken meat, liver and kidney samples by high performance liquid chromatography (HPLC). The chicken tissue sample was extracted with acetonitrile, defatted with n-hexane, and purified with an MCX solid-phase extraction cartridge. Chromatographic separation was performed on an Atlantis T3 column with the gradient elution of methyl alcohol-1% (v/v) acetic acid aqueous solution as the mobile phases at a flow rate of 1.0 mL/min. The detection wavelength was set at 292 nm. Analytes were quantified by the external standard method. The linearities of the calibration curves were well in the range of 25-1000 µg/L, and the limit of quantification was 50 µg/kg. The recoveries at different spiked levels in all the three matrices ranged from 70.91% to 103.21%, and the relative standard deviations (RSDs) were between 1.48% and 10.08% (n=6). The developed method is characterized by an excellent purification effect, sensitivity and accuracy, and can be used for the determination of benzimidazoles residue markers in chicken tissue samples.

[Simultaneous determination of monepantel and its metabolite residues in cow and sheep milk by solid phase extraction-high performance liquid chromatography-tandem mass spectrometry].

A method for the rapid and simultaneous determination of monepantel and its metabolite residues in cow and sheep milk has been developed using high performance liquid chromatography-tandem mass spectrometry. The samples were extracted with acetonitrile to precipitate the proteins and passed through a neutral alumina solid phase extraction (SPE) cartridge. The extracts were separated on an Inertsil C8-3 column (150 mm×4.6 mm, 5 µm) with a gradient elution program consisting of methanol and ammonium acetate. A triple stage quadrupole mass spectrometer equipped with an electrospray ionization source in negative ion mode was used to detect monepantel and its metabolite residues. The quantification of the analytes was performed by the external standard method. Good linear relationships between the peak areas and mass concentrations of the analytes were obtained in the range of 0.1-5.0 µg/L with correlation coefficients greater than 0.99 (n=6). The limits of quantification were 2.0 µg/kg. The recoveries of the analytes in cow and sheep milk at three spiked levels (2.0, 50, and 100 µg/kg) were in the range of 90.1%-103.3% with relative standard deviations between 2.0% and 6.2% (n=6). This method is fast, accurate, and highly sensitive, exhibits strong anti-interference capability with good recovery and repeatability, and can thus be used to simultaneously determine monepantel and its metabolite residues in cow and sheep milk.