Retention behavior of alkali, alkaline earth and transition metal cations in ion chromatography with an unmodified silica gel column

An unmodified silica gel (Develosil 30-5) column (150×4.6 mm I.D.) has been applied to the ion chromatographic separation of alkali, alkaline earth and transition metal cations. The retention behavior of the above cations on the bare substrate was investigated using a number of weak inorganic and organic acid eluents. During this investigation, several separations were achieved and the most suitable eluent conditions were identified. It was concluded that: (a) 1.5 mM HNO₃-0.5mM pyridine-2,6-dicar☐ylic acid eluent was the most effective for the simultaneous separation of common alkali and alkaline earth metal cations, (b) 1.5 mM oxalic acid eluent resulted in the best separation of alkali, alkaline earth, and transition metal cations, (c) 0.5 mM CuSO₄ eluent could be used for the separation of alkali metal cations alone and (d) 0.5 mM ethylenediamine-oxalic acid eluent at pH 5.5 resulted in themost efficient separation of both alkaline earth and transition metal cations.     

Rapid and direct determination of iodide in seawater by electrostatic ion chromatography

An electrostatic ion chromatographic (IC) method for rapid and direct determination of iodide in seawater is reported. Separation was achieved using a reversed-phase ODS packed column (250x4.6 mm I.D.) modified by coating with Zwittergent-3-14 micelles, with an eluent comprising an aqueous solution containing 0.2 mM NaClO4 and 0.3 mM Zwittergent-3-14 and using UV detection at 210 nm. Samples prepared by dissolving NaIO3, NaNO2, NaBr, NaBrO3, NaNO3, NaI, and NaSCN in artificial or real seawaters were analyzed using this IC system. Nitrite, iodate, bromide, bromate, and nitrate showed very little or no retention, while iodide and thiocyanate were well separated, being eluted within 6 and 16 min, respectively. The detection limit for iodide obtained by injecting 400 microL of sample was 0.011 microM (S/N = 3), and the precision values obtained by analyzing samples containing 0.1 or 0.3 microM iodide in real seawater samples were 2.3% RSD and 1.2% RSD, respectively. Direct determination of iodide in real seawater samples was possible using this proposed IC system.     

Metal-Assisted Oxidative Cyclization of Arylamidrazones I. Synthesis of 3-Acetyl-1,4-dihydro-1-phenyl-1,2,4-benzotriazine

Summary. In the presence of RuCl₃, N-phenylamidrazone underwent oxidative cyclization into 1,4-dihydro-1-phenyl-1,2,4-benzotriazine, the structure of which is established by spectral and X-ray diffraction data.     

Anion-exchange capillary electrochromatography with indirect UV and direct contactless conductivity detection

Conductivity detection is applied to ion-exchange capillary electrochromatography (IE-CEC) with a packed stationary phase, using a capacitively coupled contactless conductivity detector with detection occurring through the packed bed. Columns were packed with a polymeric latex-agglomerate anion-exchanger (Dionex AS9-SC). A systematic approach was used to determine suitable eluants for IE-CEC separations using simultaneous indirect UV and direct conductivity detection. Salicylate and p-toluenesulfonate were identified as potential eluant competing anions having sufficient eluotropic strength to induce changes in separation selectivity, but salicylate was found to be unsuitable with regard to baseline stability. It was also found for both indirect UV and direct conductivity detection that homogenous column packing was imperative, and monitoring of the baseline could be used to assess the homogeneity of the packed bed. Using a p-toluenesulfonate eluant, the separation of eight common anions was achieved in 2.5 min. Direct conductivity detection was found to be superior to indirect UV detection with regard to both baseline stability and detection sensitivity with detection limits of 4-25 microg/L being obtained. However, the calibration for each anion was not linear over more than one order of magnitude. When using conductivity detection, the concentration of the eluant could be varied over a wider range (2.5-50 mM p-toluenesulfonate) than was the case with indirect UV detection (2.5-10 mM), thereby allowing greater changes in separation selectivity to be achieved. By varying the concentration of p-toluenesulfonate in the eluant, the separation selectivity could be manipulated from being predominantly ion-exchange in nature (2.5 mM) to predominantly electrophoretic in nature (50 mM).     

Separation of organic and inorganic arsenic species by capillary electrophoresis using direct spectrophotometric detection

Capillary electrophoresis (CE) with UV detection was used for the determination of arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, p-aminophenylarsonic acid, 4-hydroxy-3-nitrobenzenearsonic acid, 4-nitrophenylarsonic acid, phenylarsonic acid, and phenylarsine oxide. The electrophoretic mobilities of these anionic species were determined in a 20 mM phosphate buffer in a pH range from 4 to 11, which established pH 10 as the optimum for the separation. The target analytes were then separated in a fused-silica capillary using 20 mM NaHCO(3)-Na(2)CO(3) buffer, pH 10, as electrolyte and detected at 192 nm. Both normal- and reversed electroosmotic flow (EOF) separation modes were investigated and in the latter case, poly(diallydimethylammonium chloride) (PDDAC), was used for dynamic coating of the capillary and to provide a stable and reproducible reversed EOF (relative standard deviation RSD, 0.39%). The influence of electrolyte pH and composition, applied voltage, as well as EOF reversal protocols upon the method performance criteria were investigated. The optimised method provided limits of detection for the target analytes of 1.62, 6.22, 1.45, 1.83, 0.34, 0.40, 0.40, 0.18, and 0.30 mg/L As, respectively. Linearity was obtained in the range of 0.5-40 mg/L As (for aryl compounds) and from 5-100 mg/L As (for the remaining analytes). Reproducibility of peak areas was in the range of 0.8-5.5% RSD. The method was applied to the determination of four aryl arsenic compounds used as additives in animal feed. Analytes were extracted with 40 mM hydrochloric acid - acetonitrile 4:1 v/v, and then cleaned up by passing through a C(18) solid-phase extraction cartridge before analysis by CE with detection at 200 nm. Recoveries for the four analytes were in the range of 78.8-108.3%.     

Determination of niobium(V) and tantalum(V) as 4-(2-pyridylazo)resorcinol–citrate ternary complexes in geological materials by ion-interaction reversed-phase high-performance liquid chromatography

A method for the simultaneous separation and determination of Nb(V) and Ta(V) as ternary complexes formed with 4-(2-pyridylazo)resorcinol (PAR) and citrate was developed using ion-interaction reversed-phase high-performance liquid chromatography on a C₁₈ column. Method parameters, such as pre-column complex formation conditions and composition of the complexes were investigated using spectrophotometry and HPLC. Under the optimum conditions, the Nb(V) and Ta(V) complexes were eluted within 12 min with a mobile phase of methanol–water (32:68, v/v) containing 5 mM acetate, 5 mM TBABr and 5 mM citrate buffer at pH 6.5, with detection at 540 nm. A typical separation efficiency was 33 000 and 20 000 theoretical plates per metre for Nb(V) and Ta(V), respectively. The relative standard deviation of retention times for the Nb(V) and Ta(V) complexes were 0.16% and 0.17% and for peak areas were 0.28% and 1.36%, respectively. The detection limits (signal-to-noise ratio=3) for Nb(V) and Ta(V) were 0.4 ppb and 1.4 ppb, respectively. Results obtained for standard reference rock samples agreed well with certified values and results obtained by inductively coupled plasma MS.     

A stochastic approach to the internal damage in a structure solid: Part 1: Theoretical model

The material system is considered as heterogenous medium of actual microstructural elements. These elements exhibit random geometric and physical characteristics and are further disturbed by a latitude of randomly oriented, second phase particles. A stochastic model is presented for the occurring damage process due to the nucleation and growth of microvoids under external loading. From a micromechanical point of view, the nucleation of a void at a partile-matrix interface is considered to be associated with the cut-off of the interfacial binding potential. The growth of an elemental void is seen, then, to follow a random walk of the discrete Markov type. The latter is associated with the build-up of strain in front of the tip of the advancing void and the redistribution of local stress. As the void reaches the boundary between neighbouring elements, a dicrete inter-elemental fracture process is examined in relation to the intensities of transformation within the elemental boundary.     

Crystal structures of bis(4-dimethylaminopyridinium) tetrachlorocobaltate(II) and bis-[1,3-di (ammoniummethyl)benzene]tetrachlorocobaltate(II)

The crystal structures consist of organoammonium cations hydrogen bonded to tetrahedral CoCl₄ ^2– anions. In the 4-dimethylaminopyridinium salt, [(CH₃)₂NC₅H₅NH]₂CoCl₄, pairs of cations hydrogen bond in an asymmetric fashion to two of the chlorines in each anion. The planar cations form two sets of – stacks, first parallel to the a axis and the second parallel to the b axis. The anions lie between these two nonintersecting sets of stacks. In contrast, for the second compound, [C₆H₄(CH₂NH₃)₂]CoCl₄, the tetrahedral CoCl₄ ^2– anions form layers lying parallel to the bc plane. The 1,3-di(ammoniummethyl)benzene cations crosslink adjacent anionic layers, forming a lamellar structure of alternating organic and inorganic layers.     

About the stereochemistry of intramolecular [2+2] photocycloadditions

The stereoselectivity in [2+2] photocycloaddition was studied on System I. Compounds , , and cyclize in high yield and the selectivity is higher than 94%.