Effect of complexing agent (1,10-phenanthroline) on ADP and KDP crystals

1,10-Phenanthroline (Phen) as a new additive was added into the solutions of KH₂PO₄ (KDP) and NH₄H₂PO₄ (ADP) in a small amount (∼2.5·10⁻³ M L⁻¹). The crystals were grown from the aqueous solutions of pH ∼4.5 at constant temperature by solvent evaporation technique. It leads to an increase in metastable zone width and assists the bulk growth process. The growth rate of crystals in the presence of Phen decreases considerably with an increase in impurity concentration (∼2.5·10⁻² M L⁻¹). Not much variation is observed in FTIR and XRD of pure and doped ADP/KDP. It appears that the growth promoting effect (GPE) of Phen is caused by the adsorption of the organic additive on the prism faces of ADP/KDP crystals. Higher optical transmittance is observed in the presence of the dopant. Detailed microhardness studies of ADP crystals reveal the anisotropy in the hardness behaviour. Scanning electron microscope (SEM) photographs exhibit the effectiveness of the impurity in changing the surface morphology of ADP/KDP crystals. Contrary to expectations, Phen depresses the NLO efficiency of ADP/KDP, suggesting that the molecular alignments in the presence of Phen results in cancellation effects disturbing the non-linearity.     

An effective method for enhancing metal-ions' selectivity of ionic liquid-based extraction system: Adding water-soluble complexing agent

Selective extraction-separation of yttrium(III) from heavy lanthanides into 1-octyl-3-methylimidazolium hexafluorophosphate ([C(8)mim][PF(6)]) containing Cyanex 923 was achieved by adding a water-soluble complexing agent (EDTA) to aqueous phase. The simple and environmentally benign complexing method was proved to be an effective strategy for enhancing the selectivity of [C(n)mim][PF(6)]/[Tf(2)N]-based extraction system without increasing the loss of [C(n)mim](+).     

Effect of the active component concentration in supported catalyst on the selectivity

The selectivity of heterogeneous catalytic reactions can be controlled by varying the concentration of a catalytically active component supported on a carrier. This has been confirmed by data for o-xylene oxidation on vanadium pentoxide supported on alumina.

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Effect of the acylating agent on the selectivity of anion-exchange resins and separation efficiency

Anion-exchange resins have been prepared by a two-step process that comprises the acylation of polystyrene/divinylbenzene (PS/DVB) with 50% crosslinking and subsequent amination with trimethylamine. The spacer arm between the quaternary ammonium functionality and the polymer backbone in these resins contains three, four, or five carbon atoms. An increase in the spacer arm improves the separation efficiency, affects the selectivity, and produces more symmetric peaks.     

Carrier gas as a new factor influencing the selectivity of the gas-stationary liquid phase chromatographic system

This paper generalizes studies on the influence of carrier gas on relative and absolute retention values. This line of research is also of importance due to the fact that, in the opinion of many chromatographers, the role of the carrier gas is limited only to transporting analyzed compounds along the column. However, even under conditions of the conventional capillary gas-liquid chromatography (i.e. at column pressures under 5 atm) carrier gas (its nature and pressure) significantly influences retention and separation of the analyzed compounds. First, carrier gas (N2 and CO2, for example) dramatically affects relative retention values. For this reason, one should use limit values of alpha(ij) (0) = lim alpha(ij)(P(av)) and I(i)(0) = lim Ii(Pav) I(0) = limI(i) (Pav) with Pav-->0 as chromatographic constants, rather than traditional relative retention values alpha(ij)(P(av)) and I(i)(P(av)). Second, the average pressure Pav of the carrier gas in a column and the nature of the carrier gas influence the selectivity of the gas-stationary liquid phase chromatographic system. Third, wishing to maximize the role of the carrier gas as a factor that improves separation of analyzed compounds, we should design a special gas chromatograph that would allow work with pressures in the column up to 30-50 atm.     

Enhanced flux and selectivity of metals through a dialysis membrane by addition of complexing agents to receiving phase

The transport fluxes of Cu²⁺ and Ni²⁺ from single and binary feed solutions through a dialysis membrane to a receiving solution containing complexing agent were measured at 298 K. Two complexing agents, polyethylenimine (PEI) and ethylenediaminetetraacetic acid (EDTA) were selected. Experiments were performed at different feed concentrations of metals (1.5∼34.5 mol/m³), receiving concentrations of the complexing agent (0∼25.6 mol/m³), and current densities (0∼185 A/m²). It was shown that the fluxes and selectivity factors of metal ions were enhanced with increasing concentrations of metals and the complexing agents. In contrast to the absence of applied voltage, the fluxes of metals were significantly increased but the selectivity factor of Cu²⁺ over Ni²⁺ reduced in the presence of electric field.     

Optimization of the selectivity of a cyanopropyl stationary phase for the gas chromatographic analysis of trans fatty acids

The quantification of monounsaturated and polyunsaturated trans fatty acids in partially hydrogenated fats by gas-liquid chromatography on a CP-Select CB-FAME capillary column was optimized using equivalent chain length values of fatty acids methyl esters that could coelute in the temperature range from 155 to 200 degrees C. The most appropriate temperature for the simultaneous determination of these trans isomers is around 197 degrees C. It is proposed a system to discriminate trans from cis octadecenoic fatty acid methyl esters based on the angular coefficient values of the equivalent chain length curves. The limits of detection and quantification were 0.28 and 0.93 mg g(-1). Quantification was performed in the range from 0.93 to 280 mg g(-1). Quantification accuracy was estimated by spike recovery of elaidic and trans-13-octadecenoic acids in hydrogenated fat samples. The obtained levels were from 97.60 to 103.28% for elaidic acid and from 98.12 to 99.27% for trans-13-octadecenoic acid. These results indicate that the accuracy of the methodology proposed for the quantification of monounsaturated and polyunsaturated trans fatty acids in hydrogenated fats is adequate.     

Preparation and chromatographic evaluation of new branch-type diamide-embedded octadecyl stationary phase with enhanced shape selectivity

A novel branch-type diamide-embedded octadecyl stationary phase was prepared by facile amidation. The preparation of this new phase involves the synthesis of new bifunctional silane ligand and surface modification of spherical silica via anchoring of silane coupling agent. The obtained diamide-embedded octadecyl stationary phase demonstrated excellent hydrophobic selectivity, as well as enhanced shape and planarity selectivity in comparison to commercial polymeric and monomeric C₁₈ phases, respectively, as revealed by the systematic investigation into its liquid chromatographic retention of isomeric polycyclic aromatic hydrocarbons. The applicability of this new stationary phase was further testified by the effective separation of isomeric compounds belong to different chemical classes, including chain isomers of alkylbenzenes, and positional isomers of substituted aromatics. An in-depth analysis of the separation mechanisms other than molecular shape recognition involved in the new stationary phase was performed using a linear solvation energy relationships model and compared with its monoamide and pure C₁₈ counterparts correspondingly. The performance of the new stationary phase in quantitative analysis of phenols from real-world samples was also evaluated.     

Ion-interaction chromatographic separation of metal cations in the presence of complexing agents

The mechanism of the separation of selected divalent metal cations (Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Mn²⁺, Fe²⁺ and Pb²⁺) by ion-interaction chromatography (IIC) in the presence of complexing agents has been investigated; the dependence of the retention of the analyte on the concentration of the complexing ligand has been studied. Separations have been obtained on an octadecyl-bonded silica column, mobile phases containing an ion-interaction agent (octane sulfonate), eluting cations (Na⁺ ions) and a complexing ligand (oxalate anions).     

Use of tetracycline as complexing agent in radiochemical separations

The use of the antibiotic agent tetracycline for analytical purposes in solvent extraction procedures is presented. Individual extraction curves for the lanthanides, zinc, scandium, uranium, thorium, neptunium and protactinium were obtained. Separation of those elements one from another, and of uranium from selenium, bromine, antimony, barium, tantalum and tungsten was carried out. In all cases benzyl alcohol was the diluent used to dissolve tetracycline hydrochloride. Sodium chloride was used as supporting electrolyte for the lanthanide separations and sodium perchlorate for the other elements mentioned. Stability or formation constants for the lanthanide complexes as well as for thorium complex with tetracycline were determined by using the methods of average number of ligands, the limiting value (for thorium), the two parameters and the weighted least squares. For the lanthanides, the stability constants of the complexes Ln(TC)₃ go from 9.35±0.22 for lanthanum up to 10.84±0.11 for lutetium. For the Th(TC)₄ complex the formation constant is equal to 24.6±0.3. Radioisotopes of the respective elements were used for the determinations. When more than one radioelement was present in an experiment, a multichannel analyser coupled to Ge(Li) or NaI(Tl) detectors was used for counting the activities. When only one radioisotope was used, counting of the radioisotopes was made with a single-channel analyser (integral mode counting) coupled to a NaI(Tl) detector. Uranium was determined by activation analysis (epithermal neutrons). Radioisotopes of the elements were obtained by irradiation in the IPEN swimming-pool reactor. The natural radioisotope^{2 3 4}Th was used as label in the thorium experiments. In some separation procedures such as in the case of the pair uranium-neptunium, and of the pair scandium-zinc, the separation was obtained by properly adjusting the pH value of the aqueous phases, before the extraction operation. In other cases, addition of masking agents to the extraction system was required in order to perform the separation between the elements under study. In this way ethylenediaminetetraacetic acid (EDTA) was used as masking agent for scandium and the lanthanides in order to allow separation of uranium from those elements. Diethylenetriaminepentaacetic acid (DTPA) was used as masking agent for thorium in order to extract uranium into the organic phase. Separations of protactinium from thorium, and of uranium from protactinium and thorium, were accomplished by using sodium fluoride as masking agent for protactinium and DPTA as masking agent for thorium and protactinium at the same time. In the case of the separation of the lanthanides one from another it is necessary to resort to a multi-stage extraction procedure since the stability constants for those elements are too close.     

Effect of phase composition of palladium-ruthenium membrane catalyst on selectivity of dehydrolinalool hydrogenation

Conclusions When the hydrogenation of dehydrolinalool to linalool is run on a Pd alloy containing 6 wt.% of Ru, which is lean in the -hydrogen phase, the selectivity is much greater than when the amount of the -hydrogen phase is greater. A high selectivity of the hydrogenation is achieved by reducing to a definite limit the amount of hydrogen in the membrane catalyst without using inhibitors of the side reactions, which can contaminate the hydrogenation products.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 926–928, April, 1984.     

Gas chromatographic study of complexing in the system hydrazoic acid-tributyl phosphate-nitric acid-uranyl nitrate

Elution gas chromatography has been used to study complexing of hydrazoic acid with tributyl phosphate (TBP) in hexadecane solution in the presence of nitric acid and/or uranyl nitrate. The study covered the temperature range 298-338 K, with concentrations of either additive up to 0.41 mol dm(-3). The results for hydrazoic acid elution at infinite dilution establish (a) that stoichiometry of the TBP-HNO3 complex is 1:1 and (b) that both 2:1 and 1:1 TBP-UO2(NO3)2 complexes co-exist in the system, the latter increasing in amount as the temperature is raised. Both HNO3 and UO2(NO3)2 act simply to reduce the amount of TBP free to form the 1:1 TBP-HN3 complex. Stability constants for the equilibrium UO2(NO3)2 TBP+TBP4<-->UO2(NO3)2 x 2TBP are presented.     

极谱法研究金属配合物时滴汞电极表面配位剂平衡浓度的一般表达式

在金属配合物的极谱研究中,往往需要知道配位剂 X~b-在汞滴表面的平衡浓度[X]_o.作者曾用扩散电流理论,在配位剂 X(b-)与 H~ 不配合时,导出了一个金属离子各级单核配合物在汞滴表面还原为汞齐时的[X]_0表达式.最近,作者又得到了一个普适性更好的[X]_0表达式.它不仅能把文献中更多的[X]_0表达式在同一理论基础上统一起来,而且还可在新的条件下得到一系列新的[X]_0表达式.表达式的推导设在所讨论的缓冲溶液中,加有高价金属离子 M~(n )(M),低价金属离子 M~((n-a) )(M′),配位剂 X~(b-)(X)和足量的支持电解质.在溶液本体中和汞滴表面上,X~(b-)分别与 M~(n )、M~((n-a) )、氢离     

Effects of the porous structure of particles on selectivity in liquid chromatographic systems

The effects produced in liquid-solid chromatography by the heterogeneity of adsorbent particles on the behaviour of a number of substances were studied. As adsorbent silica gels were used which varied

• a) In specific surface area and pore size,
• b) In the diameter of particles of the same microporous structure.

A second series of experiments was conducted at various temperatures. The dependences which were based on measurements of equivalent retention volumes were found to deviate somewhat from those theoretically predicted. However, they confirm and supplement some previous observations [l–5] according to which mass transport may be effected by only a portion of the packing particles if their porous structure is adequately heterogeneous. These observations are in contrast with views expressed by some authors [6, 7] who maintain that differences in mass transport resistance may only result in peak deformation. It has also been demonstrated that the effects of the heterogeneity of particle structure in liquid chromatographic systems can be reduced by increasing the temperature.     

Ion-exchange selectivity and chromatographic separation of trivalent metals on titanium antimonate

Summary The ion exchange selectivity of trivalent metal ions has been determined on titanium antimonate cation exchanger prepared by coprecipitation of antimony to titanium at different mole ratios. The selectivity sequence Al³⁺<Cr³⁺<Ga³⁺<In³⁺<Fe³⁺ was found for trivalent metal ions at an initial concentration of 10^–4 mol dm^–3 in nitric acid media. A high separation factor ^Ga/Al = Kd^Ga/Kd^Al, 4.8×10³, was observed for the Ga³⁺–Al³⁺ pair on titanium antimonate with an antimony to titanium ratio of 0.34. The effective separation of Ga³⁺ and In³⁺ from Al³⁺ was achieved using a 3 cm×0.5 cm i.d. column containing titanium antimonate with an antimony to titanium ratio of 0.34.     

Effect of pH and salt concentration on the phase inversion of particle-stabilized foams

The effect of pH and salt concentration on the phase inversion of silica particle-stabilized foams is presented. Inversion from a water-in-air powder to an air-in-water foam can be achieved by increasing the pH of the aqueous phase. By contrast, an increase in the salt concentration causes a nonfoaming aqueous dispersion to foam. The results are rationalized in terms of changes in the hydrophobicity of the solid surfaces, probed by measurement of the contact angles of water drops on hydrophobized glass slides in air.