Influence of injection parameters on column performance in nanoscale high-performance liquid chromatography

Summary The influence of the injection volume and the sample solvent on column efficiency has been evaluated in packed nano liquid chromatography using columns 150μ i.d. Evaluation of column performance was by means of reduced plate height (h) versus reduced velocity (v) for four polyaromatic hydrocarbon test compounds (PAHs). When compounds are dissolved in a weak solvent (such as MeCN: H₂O, 30∶70), and whatever the injection volume −60 or 200 nL-a gain in efficiency can be observed due to the well-known on-column focusing phenomenon, but keeping constant solute retention factors. Under optimized conditions (flow rate: 150 nLmin⁻¹, solvent sample MeCN: H₂O, 30∶70, injection volume 200 nL), a reduced plate height of 1.83 has been obtained for a 15 μm C₁₈ packing corresponding to 36000 plates m⁻¹, which illustrates the absence of any extracolumn band broadening under nano LC conditions.     

Observations on the effect of temperature on performance and stability of anion exchange columns in ion chromatography

Summary The influence of column temperature on elution behaviour of several ions on anion-exchange resin beds of the Dionex Ion Pac type was investigated. Iodate, bromate, bromide and iodide ions were separated on Ion Pac AS9SC column in the temperature range of 10°C–55°C, using NaHCO₃/Na₂CO₃ and NaHCO₃ eluents. Free energy, enthalpy and entropy changes for respective ion exchange reactions were calculated and compared with literature data for classical gel type exchangers. In most cases the enthalpy change was a function of temperature. The work at elevated temperatures caused progressing resin degradation i.e. loss of strongly basic groups, accompanied by formation of weakly basic groups and also some weakly acidic groups. Similar resin degradation was observed for Ion Pac AS5 column. Observations on the changes of the plate height with the retention factor and temperature lead to conclusion that in some circumstances longitudinal diffusion in the resin phase also contributes to the total plate height.     

Position of starting spot in TLC: Influence on average plate height

Summary The influence of the distance between the solvent entry and the starting zone positions, Z₀, on the average plate height was studied. This factor was found to be of major importance and could be optimized. The Guiochon and Siouffi model greatly underestimates the plate height for low values of Z₀.     

Cerium luminescence in nd perovskites

The luminescence of Ce³⁺ in perovskite (ABO₃) hosts with nd⁰ B-site cations, specifically Ca(Hf,Zr)O₃ and (La,Gd)ScO₃, is investigated in this report. The energy position of the Ce³⁺ excitation and emission bands in these perovskites is compared to those of typical Al³⁺ perovskites; we find a Ce³⁺ 5d¹ centroid shift and Stokes shift that are larger versus the corresponding values for the Al³⁺ perovskites. It is also shown that Ce³⁺ luminescence quenching is due to Ce³⁺ photoionization. The comparison between these perovskites shows reasonable correlations between Ce³⁺ luminescence quenching, the energy position of the Ce³⁺ 5d¹ excited state with respect to the host conduction band, and the host composition.     

Syntheses and structures of nine-coordinate K3[DyIII(nta)2(H2O)]·5H2O and eight-coordinate (NH4)3[DyIII(nta)2] complexes

K₃[Dy^III(nta)₂(H₂O)]·5H₂O and (NH₄)₃[Dy^III(nta)₂] have been synthesized in aqueous solution and characterized by IR, elemental analysis and single-crystal X-ray diffraction techniques. In K₃[Dy^III(nta)₂(H₂O)]·5H₂O the Dy^III ion is nine coordinated yielding a tricapped trigonal prismatic conformation, and its crystal belongs to monoclinic system and C2/c space group. The crystal data are as follows: a = 15.373(5) Å, b = 12.896(4) Å, c = 26.202(9) Å; β = 96.122(5)°, V = 5165(3) ų, Z = 8, D _c = 1.965 g·cm^?3, μ = 3.458 mm^?1, F(000) = 3016, R ₁ = 0.0452 and wR ₂ = 0.1025 for 4550 observed reflections with I ≥ 2σ(I). In (NH₄)₃[Dy^III(nta)₂] the Dy^III ion is eight coordinated yielding a usual dicapped trigonal anti-prismatic conformation, and its crystal belongs to monoclinic system and C2/c space group. The crystal data are as follows: a = 13.736(3) Å, b = 7.9389(16) Å, c = 18.781(4) Å; β = 104.099(3)°, V = 1986.3(7) ų, Z = 2, D _c = 1.983 g·cm^?3, μ = 3.834 mm^?1, F(000) = 1172, R ₁ = 0.0208 and wR ₂ = 0.0500 for 2022 observed reflections with I ≥ 2σ(I). The results indicate that the difference in counter ion also influences coordination numbers and structures of rare earth metal complexes with aminopolycarboxylic acid ligands.     

Solid-Phase Synthesis and Dielectric Properties of Materials Based on LaAlO<Subscript>3</Subscript>–CaTiO<Subscript>3</Subscript> System

Effect of synthesis conditions on the formation and dielectric characteristics of materials based on the La_0.33Ca_0.67Al_0.33Ti_0.67O₃ phase was studied. It is shown that the new approach suggested in the study to obtaining ceramic materials based on the LaAlO₃–CaTiO₃ system via introduction of an excess amount of Al₂O₃ over the stoichiometry of L_a0.33Сa_0.67Ti_0.67Al_0.33O₃ results in that a finely grained material is formed with relative permeability ε = 45, temperature coefficient of the relative permittivity τ_ε =–66 × 10^–6 K^–1, dielectric losses tan δ = 2 × 10^–4, and quality factor Q = 4700 at f = 9 GHz. The functional characteristics of the resulting material are comparable with the parameters of the materials synthesized by chemical coprecipitation and indicate that its use in elements of microwave electronics is promising.     

Role of Acid-Base Equilibria in the Reduction of Selenious(IV) Acid

ABSTRACT

Electroanalytical methods have been widely used for determination of Se(IV), but the nature of the reduction processes involved is not well understood. Polarographic reduction occurs in three waves (i₁, i₂, and i₃) the height of which changes with pH. We proved that in wave i₁, H₃SeO₃ ⁺ is reduced, in i₂ H₂SeO₃, and in i₃ HSeO₃ ^-. SeO₃ ^2? is not reducible. All reductions involve a transfer of six electrons and yield selenides. Limiting currents are controlled by the rate of protonation. As proton donors, in addition to H₃O⁺, the acid forms of the buffer present also act. Limiting currents increase markedly with increasing concentration of the buffer. Tenfold increase in buffer concentration can result in up to 200% increase in limiting current.     

Silver(I) ions-enhanced electrochemiluminescence of tris(2,2-bipyridyl)ruthenium(II)

In this paper, we demonstrate an electrochemiluminescence (ECL) enhancement of tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) by the addition of silver(I) ions. The maximum enhancement factor of about 5 was obtained on a glassy carbon electrode in the absence of co-reactant. The enhancement of ECL intensity was possibly attributed to the unique catalytic activity of Ag⁺ for reactions between Ru(bpy)₃³⁺ with OH. The higher enhancement was observed in phosphate buffer solutions compared with that from borate buffer solutions. This resulted from the fact that formation of nanoparticles with large surface area in the phosphate buffer solution exhibited high catalytic activity. The amount of Ag⁺, solution pH and working electrode materials played important roles for the ECL enhancement. We also studied the effects of Ag⁺ on Ru(bpy)₃²⁺/tripropylamine and Ru(bpy)₃²⁺/C₂O₄²⁻ ECL systems.     

Syntheses and Structure Determination of Nine-Coordinate (NH4)3[TbIII(nta)2(H2O)]·4H2O and Eight-Coordinate (NH4)3[ErIII(nta)2] Complexes

Syntheses and structure determination of Tb^III and Er^III complexes with nitrilotriacetic acids (nta) are reported. Their crystal and molecular structures, molecular formulas, and compositions were determined by single-crystal X-ray structure analyses and elementary analyses, respectively. The crystal of the (NH₄)₃[Tb^III(nta)₂(H₂O)]·4H₂O complex belongs to the monoclinic crystal system and C2/c space group. Crystal data are as follows: a = 16.357(8) Å, b = 8.552(4) Å, c = 17.390(9) Å, β = 104.748(7)°, V = 2352.6(19) ų, Z = 4, Mr = 675.32, D_c = 1.932 g·cm⁻³, μ = 3.112 mm⁻¹, and F(000) = 1368. The final R and Rw are 0.0220 and 0.0494 for 2357 (I > 2σ(I)) unique reflections, R and Rw are 0.0266 and 0.0510 for all 5613 reflections, respectively. The Tb^IIIN₂O₇ moiety in the [Tb^III(nta)₂(H₂O)]³⁻ complex anion has a pseudo-monocapped square antiprismatic nine-coordinate structure, in which the eight coordinate atoms (two N and six O) are from two nta ligands and the water molecule is coordinated to the central Tb^III ion directly as the ninth coordinate atom. The crystal of the (NH₄)₃[Er^III(nta)₂] complex belongs to the trigonal crystal system and R-3^c space group. Crystal data are as follows: a = 7.9181(16) Å, b = 7.9181(16) Å, c = 54.27(2) Å, γ = 120°, V = 2946.7(14) ų, Z = 6, Mr = 597.61, D _c = 2.021 g·cm⁻³, μ = 4.345 mm⁻¹, and F(000) = 1770. The final R and Rw are 0.0295 and 0.0673 for 677 (I > 2σ(I)) unique reflections, R and Rw are 0.0366 and 0.0700 for all 4827 reflections, respectively. The Er^IIIN₂O₆ part in the [Er^III(nta)₂]³⁻ complex anion is an eight-coordinate structure with a pseudo-dicapped octahedron, in which the eight coordinate atoms (two N and six O) are from two nta ligands.Original Russian Text Copyright © 2004 by J. Wang, X. D. Zhang, Y. Wang, Y. Zhang, Z. R. Liu, J. Tong, and P. L. Kang__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1067–1075, November–December, 2004.     

The structure of a triosmium carbonyl cluster-phenylarsine oxide derivative

The reaction between the dihydride of decacarbonyltriosmium [H₂Os₃(CO)₁₀] and phenyl arsine oxide (PAO) in benzene yields only one product [Os₃(O)₉(μ-H){μ-PhAs(O)OAsPh}] (1), which is characterized by high resolution mass spectrometry (HRMS), Fast Atomic Bombardment Mass Spectrometry (FAB)⁺, IR, ¹H and ¹³C NMR, and single crystal X-ray diffraction. The solid state X-ray diffraction study of compound (1) shows that the molecule is polycyclic and has an osmium triangle with a bridging hydride bonded to a PhAs(O)-O-AsPh ligand.     

A Simple Low-Cost Conductivity Cell for Flow Analysis Measurements

Abstract

A versatile low-cost conductivity flow-cell design is proposed. Its characteristics permit discrete variations in the cell volume and in the electrode area/distance ratio by varying the sealing gasket thickness, favoring high sensitivity applications in continuous flow measurements. Its dynamic characteristics as a flow conductivity detector were observed using a single-line FIA system and standard KC1 solutions, while its performance in routine work was tested by determining the NH₄ ⁺ content in plant Kjeldahl digests using FIA processing. These results are in good agreement with those obtained by the usual distillation/titration method.     

Analysis of the area of material really tested by TMA

Deformation distribution within the specimen beneath the thermomechanical analysis (TMA) probe, found by using the finite element method (FEM), depends mainly on penetration depth, specimen thickness and diameter as well as on radius of the probe tip when the Poisson’s ratio influences it just slightly. For standard radius of the tip R_o=1 mm, most deformation is distributed in a material layer up to 0.5 mm thick independently on elastic modulus of a polymer at a glassy state. It is caused by the fact that maximal penetration depth for the polymers usually equals to about 0.05 mm. Because of this, the contact surface area is less than 0.17 mm² for the standard radius of the tip. This evidences that predominantly the specimen volume equal to  mm² (depth×area) is tested by the TMA at compression mode. For R_o=5 mm is tested the layer 2.5 mm thick. This makes possible to evaluate the material properties in the zone of different thickness depending on radius of the tip.     

RECTIFYING EFFECT OF POLYANILINE(PANI)/N-TYPE POROUS SILICONE HETEROJUNCTION*

Heterojunctions between polyaniline (PANI) and n-type porous silicon (PS), Al/PS-PANI/Au cell,were fabricated, and the rectifying parameters of this heterojunction diode were measured as a function of thepreparation conditions of PANI and PS, the electronic structure of PANI as well as cell structure. Therectifying parameters of Al/PS-PANI/Au cell were determined to be γ= 1 .8×10~1～ 1 .0×10~5 for the rectifyingratio at 3V, n = 3 ～12 for the ideal factor,j_0 = 8.0×10~(-5)～5.6×10~(-2) mA/cm~2 for the reversed saturated currentdensity, and φ_b = 0.67～ 0.83 V for the barrier height, respectively. The best rectifying heterojunction diodemade between PANI and n-type PS with higher rectifying factor (γ= 1 .0×10~5 at 3V ), output current (>1500mA/cm~2 at 3V) and lower ideal factor (n = 3.3) was obtained by preventing the oxidation of PS beforeevaporating Al electrode.     

A new type of charge compensating mechanism in Ca5(PO4)3F:Eu phosphor

The X-ray powder diffraction, reflectance, photoluminescence, photoluminescence excitation and ESR spectra of Ca₅(PO₄)₃F:Eu³⁺ phosphor have been studied. Three distinct variants of calcium substitutional Eu³⁺-sites have been observed in this host and the charge compensating species related to each of these sites has been identified. It is noted that the host related trace impurities those have prospects of acting as charge compensator, and the reaction environment that exists during the preparation of the material, greatly influence the preferential substitution of different Ca²⁺-sites by the Eu³⁺ ions. It is also noted that the charge compensating species in a suitable case, takes part in the photophysical process of luminescence of the Eu³⁺.     

Synthesis and spectral characteristics of Sr2Y8(SiO4)6O2: Eu polycrystals

Spectral-luminescent characteristics of Sr₂Y₈(SiO₄)₆O₂: Eu powder crystal phosphor with the apatite structure and high-intensity luminescence of Eu³⁺ ions have been studied. The charge state of europium in the samples has been characterized by means of X-ray L₃-adsorption spectroscopy. It was established that Eu³⁺ forms two types of optical centers. Besides, luminescence of Eu²⁺ions was found. Reduction Eu³⁺→Eu²⁺ was considered, which may be due to vacancy formation in the 4f crystal lattice position and to negative charge transfer by this vacancy to two ions. Thus, in the silicate lattice there exist inhomogeneously distributed oxygen-deficient centers, which are responsible for nonradiative transfer of excitation energy to Eu³⁺ and Eu²⁺ ions. To study electron-vibrational interactions in the crystal phosphor samples, their IR and Raman spectra were examined. In the luminescence spectrum of Eu²⁺, a series of low-intensity bands caused by interaction of the 4f⁶5d state of Eu²⁺ with silicate lattice vibrations was observed.     

Structural and P NMR investigation of Bi(MM′)2PO6 statistic solid solutions: Deconvolution of lattice constraints and cationic influences

Two solid solutions BiM_xMg_(2−x)PO₆ (with M²⁺=Zn or Cd) have been studied through ³¹P MAS NMR. The analysis has been performed on the basis of refined crystal structures through X-ray diffraction and neutron diffraction. The BiZn_xMg_(2−x)PO₆ does not provide direct evidence for sensitive changes in the phosphorus local symmetry. This result is in good agreement with structural data which show nearly unchanged lattices and atomic separations through the Zn²⁺ for Mg²⁺ substitution. On the other hand, the Cd²⁺ for Mg²⁺ substitution behaves differently. Indeed, up to five resonances are observed, each corresponding to one of the five first-cationic neighbour distributions, i.e. 4Mg/0Cd, 3Mg/1Cd, 2Mg/2Cd, 1Mg/3Cd and 0Mg/4Cd. Their intensities match rather well the expected weight for each configuration of the statistical Cd²⁺/Mg²⁺ mixed occupancy. The match is further improved when one takes into account the influence of the 2nd cationic sphere that is available from high-field NMR data (18.8 T). Finally, the fine examination of the chemical shift for each resonance versus x allows to de-convolute the mean Z/a² effective field into two sub-effects: a lattice constraint-only term and a chemical-only term whose effects are directly quantifiable.     

Determination of sophoridine and related lupin alkaloids using tris(2,2′-bipyridine)ruthenium electrogenerated chemiluminescence

Electrogenerated chemiluminescences (ECLs) based on tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺) and lupin alkaloids, for instance, sophoridine (SRI), matrine (MT), sophoranol (SR) and sophocarpine (SC) in an aqueous alkaline buffer solution (pH 9.0) are studied. The light emission is mainly caused by an electro-oxidation reaction between tertiary amino group on the alkaloid compounds and Ru(bpy)₃²⁺ in a thin layer flow cell equipped with a glassy carbon disc electrode (22.1 mm²) at the potential of +1.50 V (versus Ag/AgCl). The luminescence wavelength of 610 nm confirmed that ECL is caused by Ru(bpy)₃^2+∗ to its ground state. ECL intensities of these lupin alkaloids are affected by the substituent character, three-dimensional conformation of hydrogen on β-carbon atom. Ionization potentials taken from calculation data further confirm the experimental results. In addition, the factors affecting the determination and HPLC separation of the four alkaloids are also investigated.     

Comparative study of efficiency and reproducibility of two high-performance gel permeation chromatography columns with microparticulate packings

Two kinds of commercially available, microparticulate silica columns have been studied for their efficiency and reproducibility in gel permeation chromatography measurements. Results are provided for column plate height measurements, dispersity, and specific resolution as a function of flow rate. The influence of injection volume and slice width on these measurements is also presented. Reproducibility studies on polystyrene and styrene-n-butyl methacrylate copolymer are reported.     

H and C NMR spectroscopy of 9-acridinones

The ¹H and ¹³C NMR spectra of 9-acridinone and its five derivatives dissolved in CDCl₃, CD₃CN and DMSO-d₆ were measured in order to reveal the influence of the constitution of the compounds and features of the solvents on chemical shifts and ¹H-¹H coupling constants. Experimental data were compared with theoretically predicted chemical shifts, on the GIAO/DFT level of theory, for DFT (B3LYP)/6-31G^∗∗ optimized geometries of molecules—also for four other 9-acridinones. This comparison helped to ascribe resonance signals in the spectra to relevant atoms and enabled revelation of relations between chemical shifts and physicochemical features of the compounds. It was found that experimentally or theoretically determined ¹H and ¹³C chemical shifts of selected atoms correlate with theoretically predicted values of dipole moments of the molecules, as well as bond lengths, atomic partial charges and energies of HOMO.     

The actual structure of K6(VO)2(V2O3)2(PO4)4(P2O7): Ordered distribution of P2O7 groups and charge ordering of vanadium

The actual structure of the vanadium phosphate K₆(VO)₂(V₂O₃)₂(PO₄)₄(P₂O₇) has been determined, using a much larger single crystal than previously used for the isostructural Rb-phase. The actual supercell is four times larger than the corresponding orthorhombic subcell with , , , α=β=γ=90°. The structure resolution, performed in the triclinic space group C-1, shows that the P₂O₇ groups alone are responsible for the superstructure, all the other atoms keeping the atomic positions of the orthorhombic subcell. This structural study shows a perfect ordering of the P₂O₇ groups in the actual structure, in contrast to the results obtained from the subcell. Concomitantly, the V⁴⁺ and V⁵⁺ are found to be ordered in the form of [110] stripes.