On the statistical independence of various column contributions to band broadening. Part 3: Independent treatment of longitudinal diffusion in the plate model

It is shown theorectically that the classical formula for calculating the theoretical plate number from squared first central moment, t , and second central moment, σ², according to n _theor = t /σ² is valid only when the capacity ratio, k approaches infinity. The general relation between the classical experimental HETP value, H = L/nm _theor, and the underlying true theoretical plate height, ΔL, is found to be when (σ′)² is the total column contribution to band broadening, L is the column length, D _m is the average diffusion coefficient of the sample component in the mobile phase, D _s is its value in the stationary phase, and u is the average linear velocity of the mobile phase. The mobile phase displacement, as well as the mass exchange process, is assumed to be continuous, but the application of the plate concept conditions leads to a mass balance equation that can be interpreted as belonging to a modified discontinuous plate model. The contributions 2D _m/u and k 2 D _s/u from longitudinal sample diffusion in the mobile and stationary phases, respectively, are consistent with the assumption that the processes are statistically independent, although the common solution technique of the differential equations does not take full account of this independence.     

Influence of solvent strength in possible optimization of adsorption thin-layer chromatography

Considerations of TLC process optimization have been based on the thermodynamic theory of adsorption from multicomponent solvents using experimental and theoretical R_{M1, 2} = f (Φ₁) relationships. It was found that a relationship exists between the A_z parameter (log k where k is the partition coefficient of the substance chromatographed) of the above theory and pK_a values of substances as well as the solubility parameter δ of the mobile phase components. Analysis of the A_z values of substances shows that a slight variation therein is associated with lower selectivity of chromatographic separation.     

Theoretical determination of optimum composition of the binary mobile phase for distribution of substances in thin-layer chromatography

The measure of the distribution of a mixture of substances in TLC with a binary mobile phase is expressed as ΔRM which represents the difference between the R_M values of substances i and j on use of the binary solvent 1 + 2 as the mobile phase. The possibility of determining its maximum value at an optimum composition of the binary mobile phase is demonstrated in this paper. This value can calculated from experimental and theoretical functions R_M1,2 = f(Φ₁) of substance i and j. More simply, ΔRM can be calculated theoretically from easily measurable adsorption parameters of excess adsorption isotherms and from chromatographic parameters obtained for pure solvents. The ΔRM value calculated theoretically can be utilized in a pilot technique for determination of the optimum composition of the mobile phase in gradient liquid chromatography.     

On the estimation of extra-column contributions to band broadening through measurements on an authentic chromatogram

The time constant, τ, is determined from the tail of an authentic HPLC peak through a plot of In U versus time, t, according to the relation expected at low recorder deflexions, U. The value obtained, τ = 2.43 s, is one order of magnitude larger than an ordinary recorder time constant, which is quite normal for LC detectors. It agrees with the value, τ = 2.44 s, needed theoretically to distort a Gaussian-shaped peak so as to obtain the experiment-ally found second moment, σ² = 11.13 s,² and the experimental difference between first moment t and peak retention time t_max, t – t_max = 0.78 s. The determination is therefore regarded as a demonstration of the variance addition rule where σ is the second moment of the non-distorted peak. The column contribution version is also considered. This equation was appliied earlier to an estimation of extra-column contributions to band broadening with the aid of the “abt” concept. An explicitly k-(capacity ratio)-dependent expression for the mass exchange contribution, σ is derived from Golay's equation for capillary columns, but the validity of the Golay equation is under discussion.     

On the statistical independence of various column contributions to band broadening. Part 1: Second moment contributions from statistically independent,longitudinal diffusion in both phases

The total length-based second moment contribution from longitudinal sample diffusion in both phases on a column, σD , is derived by adding individual partial differential contributions to a partial differential equation accounting for the longitudinal diffusion processes only. Although each diffusion-dispersed sample part is equilibrated between two phases, the resulting σ,D (= 2D _mt _m + 2D _st _s) can be interpreted as the sum of two independent contributions in accordance with the variance addition rule. (D _m and D _s are the mean diffusion coefficients and t _mand t _s the mean residence times of the sample in the mobile and stationary phases, respectively.) The same σD expression is derived from the random walk model of Giddings by treating the diffusional process in each phase as statistically independent of the other processes. Under these conditions the broadening contribution from longitudinal diffusion in the mobile phase is shown to be independent of the velocity profile.     

Über geordnete Perowskite mit Kationenfehlstellen. XI. Verbindungen vom Typ ABB□1/4WVIO6 ≙ ABIIB□WO24 mit AII,BII = Ba,Sr

On Ordered Perovskites with Cationic Vacancies. XI. Compounds of Type A B B □_1/4W^VIO₆ ? A B^IIB □W O₂₄ with A^II, B^II = Ba, Sr Depending on the ionic radii of the two and three valent cations in the perovskites of type ABB □_1/4W^VIO₆ ?; AB^IIB □WO₂₄ order disorder phenomena are present. The results of the x-ray and vibrational spectroscopic investigations as well as the diffuse reflectance spectra and the visible photoluminescence are reported.     

Schwingungsspektren und Kraftkonstanten der Übergangsreihe O2PF—S2PF— S2P(CH3)

Vibration spectra and force constants of the series O₂PF — S₂PF — S₂P(CH₃). The vibrational spectra of OSPF, S₂PF, S₂PF(CH₃) and S₂P(CN) are reported and discussed with O₂PF and S₂P(CH₃). On the basis of a simplified valence-force-field the force constants are calculated and the bonding relations are discussed. In the ions, f PF is lower than in corresponding molecules. The ionic charge is distributed over nearly all atoms of the ions.     

Photoelectrochemistry with Colloidal Semiconductors; Laser Studies of Halide Oxidation in Colloidal Dispersions of TiO2 and α-Fe2O3

Aqueous sols of TiO₂ (anatase, particle radius 25 Å) were excited with (347.1 nm)-laser light and the reaction of valence-band holes with halide ions (X = I^?, Br^?, Cl^?) was investigated. Hole transfer takes place within the duration of the (10 ns)-laser pulse and results in the formation of anion radicals according to the sequence: The quantum yield of X increases in the order Cl < Br < I, attaining 0.8 for I at pH 1. It is affected by pH, halide concentration and the presence of a protective agent for the sol. RuO₂ deposited onto TiO₂ enhances markedly Cl and Br -formation, but has no effect on the yield of I. Laser-photolysis investigation of halide oxidation were also carried out with colloidal Fe₂O₃ (particle radius 600 Å). For I_2?formation, the quantum yield exceeds 0.9 indicating almost quantitative hole scavenging by iodide.     

Dibrommethylsulfoniumsalze – Darstellung und Kristallstruktur [1]

Dibromomethylsulfoniumsalts — Preparation and Crystal Structure The salts CH₃SBrA^? (A^? = SbCl, AsF) were prepared by various routes and characterized by their Ramanspectra. CH₃SBrAsF crystallized in the monoclinic space group P2₁/c with a = 770,5(4) pm, b = 942,4(12) pm, c = 1329,3(14) pm, β = 100,28(6)°, Z = 4. Distances and bond angles in the cation are as expected.     

The role of d orbitals in tetrahedral hybrid orbitals of oxy-ions

The hybrid orbitals of tetrahedral oxy-ions containing some d character have been calculated by maximum overlap method. The d characters of hybrid orbitals increase in the order of SiO, PO, SO, ClO, and decrease in order of GeO, AsO, SeO, BrO. The bond strengths are also obtained for these ions. The hybrid Orbital of VO, CrO, and MnO are of the type d³s as the result of calculation.     

Über Perowskite Ba2BBTeVIO6

On Perovskites Ba₂B B Te^VIO₆ Compounds of composition Ba₂BBTe^VIO₆ with B^I = Li, Na; B^III = La, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Yb, Y, In, Sc crystallize in a cubic 1:1 ordered perovskite structure. The vibrational spectroscopic investigations show, that more species of TeO₆ octahedra are present in the lattice.     

Explicit expression of the franck–condon factors in terms of the potentials of the two states

The calculus of the overlap integral for two states represented by the vibrational wave functions ψ and ψ is reduced to that of the Franck–Condon integral ?(0, x) = ∫ ψψ (t) dt. It is proved that for “numerical potentials” (as well as for a Dunham potential), this integral is given on each interval by a simple analytic expression in terms of the two potentials. The Franck–Condon factors are well determined by “coupling constants” related uniquely to the coordinates of the turning points of the potentials. An application to the band system BII? XΣ of Nα₂ is compared with the usual numerical methods.     

19F-NMR-spektroskopischer Nachweis und statistische Untersuchung zur Bildung der gemischten Clusteranionen [(Mo6ICl)F]2−, n = 0–7, und Darstellung von (TBA)2[(Mo6I)F]

¹⁹F NMR Spectroscopic Evidence and Calculation of the Statistical Formation of Mixed Cluster Anions [(Mo₆I Cl )F ]^2?, n = 0–7, and Preparation of (TBA)₂[(Mo₆I )F ] The octa-μ₃-iodo-hexafluoro-hexamolybdate(2?)ion [(Mo₆I)F]^2? is prepared for the first time. The system of the 21 innersphere mixed clusters (Mo₆ICl)⁴⁺, n = 0–7 is formed by exchange of innersphere bound Clⁱ against outersphere bound I^a on tempering solid [(Mo₆Cl)I] at 400°C. Prolonged tempering leads to increasing average n values of the mixture, which is converted into the tetrabutylammonium salt (TBA)₂[(Mo₆ICl)F]. Using increments of chemical shifts and integral peak intensities the 54 ¹⁹F-nmr signals of the 21 species (compound n = 8 is absent) are assigned and confirmed by the 2 D-¹⁹F/¹⁹F-COSY spectrum. From the measured intensities the distribution of the different compounds is determined and proves significant deviation from statistical occupation, revealing the preference of isomers with iodine atoms occupying edges of the innersphere cube and discrimination of those sharing diagonals of the faces. Moreover all compounds with n = 3 and 4 are present overaverage in comparison to the others.     

Assembly of Chiral Two- and Three-dimensional Copper(I) Pseudohalide Based Coordination Polymers with Asymmetrically Substituted Pyrazine and Pyrimidine Ligands

The coordination polymers [(CuCN)₂(μ-2 Mepyz)], [CuCN(μ-2 Mepyz)] and [CuCN(μ-4 Mepym)] ( 1 – 3 ) (2 Mepyz = 2-methylpyrazine; 4 Mepym = 4-methylpyrimidine) may be prepared by self-assembly in acetonitrile solution at 100 °C ( 1 , 3 ) or without solvent at 20 °C ( 2 ). All three contain [CuCN] chains that are bridged by the bidentate aromatic ligands into sheets in 1 and 3 D frameworks in 2 and 3 . Reaction of CuSCN with these heterocyclic diazines at 100 °C leads to formation of the lamellar coordination polymers [(CuSCN)(μ-2 Mepyz)] ( 4 ) and [CuSCN · (4 Mepym-κN1)] ( 5 ), which contain respectively [CuSCN] chains and trans-trans fused [CuSCN] sheets as substructures. The presence of an asymmetric substitution pattern in 2 Mepyz and 4 Mepym induces the adoption of a chiral structure by 2 and 5 (space groups P2₁2₁2₁ and P1).     

Über das Auftreten von Monoselenan- und Monotelluran-disulfandiphosphonat bei der Umsetzung von SPO mit Seleno- und Telluropolythionaten

On the Formation of Monoselenane and Monotellurane Disulphane-diphosphonate by the Reaction of SPO with Seleno and Telluropolythionates In the reaction of seleno- and telluropolythionates with SPO, SeS₂P₂O and TeS₂P₂O are formed and are described for the first time. Polysulfphane-diphosphonates, -disulphonates and -phosphonsulphonates occur as side and consecutive products. By evaluation of radiochemical double labelling with the nuclide pairs ³⁵S? ³²P and ³⁵S? ⁷⁵Se, it is possible to identify the products formed and obtain information about the reaction mechanism.     

A kinetic study of the autocatalytic permanganate oxidation of formic acid

The kinetics of the permanganate oxidation of formic acid in aqueous perchloric acid has been studied. The results indicate that this reaction is autocatalyzed by both manganese(II) ion (formed as a reaction product) and colloidal manganese dioxide (formed as an intermediate). The apparent rate constants corresponding to the noncatalytic and autocatalytic reaction pathways are given, respectively, by the following equations The activation energies associated with the true rate constants, ??, ??, ??, ??, ??, and ?? are 37.2, 62.5, 70.9, 52.5, 40.8, and 59.9 kJ mol^?1, respectively. The percentage of the total reaction corresponding to each pathway is given for typical experimental conditions. Mechanisms in agreement with the kinetic data are proposed for the six different reaction pathways observed.     

A pulse radiolysis study of I and (SCN) in aqueous solutions over the temperature range 15–90°C

The extinction coefficients and the decay kinetics of I and (SCN) have been characterized over the 15–90°C-temperature range. The extinction coefficients of I at 385 and 725 nm were determined to be 10,000 and 2560M^?1 cm^?1, respectively, based on the extinction coefficient of (SCN) at 475 nm being equal to 7600M^?1 cm^?1. At these three wavelengths, all extinction coefficients were constant over the temperature range studied. The rate of decay of both I and (SCN) was found to be a function of I^? and SCN^? concentration, respectively, as well as temperature.     

Elektronenmikroskopische Untersuchungen zur Realstruktur von La2CeTaO6Cl3 und dessen thermischem Abbauprodukt La2CeCe TaO6Cl3−x

High Resolution Electron Microscopy Investigations of La₂CeTaO₆Cl₃ and its Thermal Decomposition Product La₂Ce Ce TaO₆Cl_3?x The thermal decomposition of the hexagonal La₂CeTaO₆Cl₃ led to a mixed-valent product La₂CeCe TaO₆Cl_3?x with a complicated monoclinic structure. The detailed inspection shows two subunits A and B, which form the monoclinic unit cell by a ABAB sequence. The subunit A is almost identical to the hexagonal cell of the starting material while subunit B has additional Ln- and Cl-positions. For this reason, the main structure features of the monoclinic compound and the starting material are related, which is clearly seen in the electron microscopy investigations. As might be expected from the relationship between the subunits A and B one can observe defects in the monoclinic compound arising from the various possibilities of combining these building elements. We also found structure defects in the hexagonal starting material, which are caused by the presence of the subunit B.     

The crystal structure of tris (ethylenediamine), cobalt(III) hexacyanoferrate(III)dihydrate,Co(C2H8N2)3[Fe(CN)6] · 2H2O

The crystal structure of the title compound has been determined from three dimensional x-ray data obtained by the multiple film method. The space group is P2_l/n and the cell dimensions are: a = 14.90, b = 16.84, c = 8.38 Å; β = 93.5° Z = 4. The structure is formed by discrete Co (en) and Fe(CN) ions, both of which have an octahedral configuration. The Fe(CN) ions are approximately octahedrally surrounded by the Co (en) ions while arrangement of Fe (CN) ions around the Co(en) ions completely differs from an octahedron. The mean Fe? C and Co? C dustances are 1.91 and 2.01 Å, respectively. The water molecules do not play an important role in the structure and all distances between oxygen and other atoms indicate the presence of very weak hydrogen bonds. The salts M (en)₃ Q(CN)₆ · H₂O, where M = Co and Cr and Q = Cr, Mn, Fe and Co, are all isomorphous.     

Chemistry of Superoxide Ion as Revealed by the Differential Oxidation of Arylpyruvates

Superoxide ion apparently reacts with acidic substrates via species such as O₂, HO₂, O, HO and H₂O₂. Arylpyruvates give arylacetates and arylaldehydes indicating competing nucleophilic and free radical oxidation. Benzaldehyde is further oxidized by free radical and nucleophilic dioxygen species giving benzoic acid. p-Hydroxybenzaldehyde gives the corresponding benzoic acid which is best accounted for by HO₂, since O and O₂ are without effect. Hydroquinone is also produced presumably by nucleophilic attack of HO. Replacement of the acidic hydrogen atoms by sodium changes the product distribution in accord with these findings.