一种表面共聚氢氧根选择性阴离子色谱固定相

报道了一种基于聚(苯乙烯-二乙烯基苯)微球(PS-DVB)的表面共聚氢氧根选择性阴离子固定相。它以烯丙基缩水甘油醚(AGE)为功能单体、通过自由基引发直接与PS-DVB微球表面残留的悬挂双键共聚,再通过醇胺开环得到。考察了两种醇胺试剂对分离的影响;扫描电镜、红外光谱、元素分析表征结果表明:表面共聚反应成功在微球表面引入季胺基团,且对微球理化性质无显著影响;所得固定相表现氢氧根淋洗液的高选择性,对常规无机阴离子表现出良好的分离性能(分离度>1.5)和运行稳定性(保留时间的相对标准偏差<1.13%),其实用性通过分析茶叶样品中无机阴离子进行了展示。     

Direct separation of the enantiomers of ramosetron on a chlorinated cellulose‐based chiral stationary phase in hydrophilic interaction liquid chromatography mode

Ramosetron is an enantiopure active pharmaceutical ingredient marketed in Japan since 1996 and later in a few Southeast Asian countries predominantly as an antiemetic for patients receiving chemotherapy. In this study, a simple and rapid high‐performance liquid chromoatography method for the separation of ramosetron and its related enantiomeric impurity by using hydrophilic interaction liquid chromatography mode is presented. Chiral resolution was performed on an analytical column (100 mm × 4.6 mm id) packed with 3 μm particles of cellulose‐based Chiralpak IC‐3 chiral stationary phase. Using a mobile phase containing acetonitrile–water–diethylamine (100:10:0.1, v/v/v) and setting the column temperature at 35°C, the resolution value was 7.35. At a flow rate of 1 mL/min, the enantioseparation was completed within 5 min. The proposed method was partially validated and it has proven to be sensitive with limit of detection and limit of quantitation of the (S)‐enantiomer impurity of 44.5 and 133.6 ng/mL.     

Two-gap superconductivity in the Fe-1111 superconductor LaFeAsO1−x F x : A point-contact Andreev-reflection study

Point-contact Andreev-reflection (PCAR) experiments were performed in the Fe-1111 layered superconductor LaFeAsO_0.9F_0.1 with resistive T _c ^on ∼ 27 K. The observation of two pairs of peaks in the low-temperature Andreev-reflection spectra clearly indicates the presence of two order parameters. The behavior of the two gaps as a function of temperature, obtained by fitting the conductance curves by means of the generalized two-band Blonder-Tinkham-Klapwijk model, shows some anomalies. A theoretical analysis performed within the two-band Eliashberg theory with a generic electron-boson coupling can reproduce the low-temperature value of the two gaps but generally fails in giving a satisfactory fit of their overall temperature dependence, indicating the rich and complex physics of these newly discovered superconductors.      

Quasi-particle structure around a single vortex in high-Tc superconductors

For analyzing the checker-board like modulation of the local density of states (LDOS) around a vortex observed in the slightly overdoped Bi₂Sr₂CaCu₂O_x, we examined the effect of pseudogap state of high-T_c superconductors to the LDOS around the vortex. We first derived the Bogoliubov-de Gennes equation for d-wave superconductivity (d-SC) in the presence of d-spin density wave (d-SDW). Using the Fourier–Bessel expansion, we solved this equation for a single vortex state, numerically. We found that the peak of the bound states around E = 0 becomes small and modulation of the LDOS is observed for larger d-SDW order parameter.     

Evidence for pinning by (Sr,Ca)2CuOy particles in partial-melting processed bulk Bi2Sr2CaCu2O8+δ ceramics

Flux distributions of partial-melting processed Bi₂Sr₂CaCu₂O_8+δ ceramics are obtained using magneto-optic imaging. In remanent states (μ₀H_a=0 T), large amounts of trapped flux are observed along (Sr,Ca)₂CuO_y particles embedded in the Bi₂Sr₂CaCu₂O_8+δ matrix. Despite the relatively large size of these particles (up to 30 μm), the pinning effect is similar to that of Y₂BaCuO₅ particles in melt-processed YBa₂Cu₃O_7−δ. Furthermore, we discuss how the pinning capability of non-superconducting particles of different sizes and densities will show up in magneto-optic images.     

Unusual resistivity broadening in the mixed state of NdBa2Cu3O7−δ crystals grown by a crystal-pulling technique

In order to clarify the origin of a strong peak effect in the magnetization curve of NdBa₂Cu₃O_7−δ crystals, we investigated the superconductivity transition behavior of the in-plane resistivity in static magnetic fields up to 8 T. Comparing the results for the samples exhibiting and not exhibiting the peak effect, we found that the former (peak effect sample) shows lower resistivity above the vortex melting temperature. This implies that the pinning force is effective in the vortex liquid state. We also found that the normal state resistivity behaviors of some samples were unusual, indicating inhomogeneous current flow. These results suggest an existence of sheet-like pinning centers perpendicular to the conduction planes.     

Preconcentration of samples in sandwich tanks for continuous thin-layer chromatography

It is demonstrated that horizontai sandwich tank with two cover plates can be used to preconcentrate sample solutions. Narrow sharply-defined starting zones are obtained just outside the smaller cover plate when the series of spots of the sample solution are applied on the thin layer and predeveloped with a volatile solvent. After evaporation of the solvent, the whole area of the TLC-plate is covered with two plates and developed with a suitable solvent.     

Coherence transition in granular YBa2Cu3O7-δ, YBa2Cu2.95Zn0.05O7-δ, and YBa1.75Sr0.25Cu3O7-δ superconductors

We have studied experimentally the electrical magneto-conductivity near the superconducting transition of YBa₂Cu₃O_7-δ, YBa₂ (Cu_2.95Zn_0.05)O_7-δ and Y(Ba_1.75Sr_0.25)Cu₃O_7-δ polycrystalline samples. The measurements were performed in magnetic fields ranging from 0 to 400 Oe applied parallel to the current orientation. The results show that the resistive transition of these systems proceeds in two stages. The pairing transition occurs at the bulk critical temperature T_c, where superconductivity is stabilized within small and homogeneous regions of the sample generically called grains. The regime of approach to the zero resistance state reveals the occurrence of a coherence transition at a lower temperature T_c0. This transition is related to the connective nature of the granular samples and is controlled by fluctuations of the order-parameter phase of individual grains. Our experiments show that the Zn-doping, besides depressing the pairing critical temperature, strongly enlarges the temperature range dominated by effects related to the coherence transition. The substitution of Ba by Sr causes only a small reduction of T_c, but also enhances significantly the effects related to the grain coupling phenomenology. In general, our results indicate that these impurity substitutions in YBa₂Cu₃O_7-δ produce or magnify the granularity at a microscopic level, enhancing the effects of phase fluctuations in the conductivity near the transition.     

Doping-dependent evolution of low-energy excitations and quantum phase transitions within an effective model for high-T<Subscript>c</Subscript> copper oxides

In this paper a mean-field theory for the spin-liquid paramagnetic non-superconducting phase of the p- and n-type high-T_c cuprates is developed. This theory applied to the effective t-t'-t′′-J^* model with the ab initio calculated parameters and with the three-site correlated hoppings. The static spin-spin and kinematic correlation functions beyond Hubbard-I approximation are calculated self-consistently. The evolution of the Fermi surface and band dispersion is obtained for the wide range of doping concentrations x. For p-type systems the three different types of behavior are found and the transitions between these types are accompanied by the changes in the Fermi surface topology. Thus a quantum phase transitions take place at x = 0.15 and at x = 0.23.Due to the different Fermi surface topology we found for n-type cuprates only one quantum critical concentration, x = 0.2. The calculated doping dependence of the nodal Fermi velocity and the effective mass are in good agreement with the experimental data.     

Electronic structure of spin-chain compounds: common features

The incommensurate composite systems M₁₄Cu₂₄O₄₁ (M = Ca, Sr, La) are based on two fundamental structural units: CuO₂ chains and Cu₂O₃ ladders. We present electronic structure calculations within density functional theory in order to address the interrelations between chains and ladders. The calculations account for the details of the crystal structure by means of a unit cell comprising 10 chain and 7 ladder units. It turns out that chains and ladders can be treated independently, which allows us to introduce a model system based on a reduced unit cell. For the CuO₂ chains, we find two characteristic bands at the Fermi energy. Tight binding fits yield nearest and next-nearest neighbour interactions of the same order of magnitude.