Optimization of a multisolvent composition in RP-HPLC: Convenient criterion for preliminary search for the best eluent strength

Summary Interpretive methods are very commonly used to direct the search for the optimum solvent composition. For multisolvent systems, the composition search space is often reduced to one straight line (ternary systems with two organic modifiers), three straight lines (three ternary systems with each possible pair of the organic modifiers of the tetrahedron) — or a plane delimited by a triangle (quaternary systems inside the solvent tetrahedron). In each case, the space is restricted by binary compositions of equal solvent strength, in such a way that through it, the analysis time remains approximately constant. This restricted space is defined without taking into account any selectivity criterion between peaks, and consequently, if a given pair of peaks is badly resolved with the considered binary solvents, the probability of any mixture of them improving the peak selectivity will be very low. The ability to calculate the retention models in a binary solvent system from two linear gradient runs, allows the prediction of the selectivity for each pair of solutes into each binary solvent system (ACN/Water, MeOH/Water, THF/Water) from six preliminary linear gradient runs, and then, to determine and eliminate all the sets of isoeluotropic binary compositions that will offer little hope of giving useful separation conditions with multisolvent systems and, at the same time, to select the most promising set of binary compositions. The selectivity and the total time of the chromatogram are the two parameters that are considered for this search. When several possiblities are found, priority is given to the simplest solvent system (binary rather than ternary and ternary rather than quaternary). Reducing the number of preliminary experiments and improving the accuracy of the predicted optimum are the two objectives of this approach. Its practical interest is discussed by comparing the results obtained for an illustrative separation to those obtained with another existing method.     

Copper Incorporated [Me2(15)dieneN4] Macrocyclic Complex for Fabrication of PVC based Membrane Electrode for Copper

Copper (II) complex of 2,4-dimethyl-1,5,9,12-tetraazacyclopentadeca-1,4-diene, [Me₂(15)dieneN₄] was synthesized and used in the fabrication of Cu²⁺ – selective ISE membrane in PVC matrix. The membrane having Cu(II) macrocyclic complex as electroactive material along with sodium tetraphenyl borate (NaTPB) as anion discriminator. Dibutyl phthalate (DBP) as plasticizer in poly(vinyl chloride) (PVC) matrix was prepared for the determination of Cu²⁺. The best performance was observed by the membrane having Cu(II) complex–PVC–NaTPB–DBP with composition 1:5:1:3. The sensor worked well over a concentration range 1.12 × 10⁻⁶ M–1.0 × 10⁻¹ M between pH 2.1–6.2 and a fast response time 10±2 s and a lifetime of 6 months. Their performance in partially non-aqueous medium was found satisfactory. Electrodes exhibited excellent selectivity for Cu²⁺ ion over other mono-, di-, trivalent cations. It can also be used as indicator electrode in the potentiometric titration of Cu²⁺ against EDTA as well as in the determination of Cu²⁺ in real samples.     

Structure of copper and nickel amine complexes with polyoxometallates and their adsorption properties relative to lower alcohols

The rates of the adsorption and desorption of methanol and ethanol vapor to and from compounds formed by cationic copper(II) and nickel(II) amine complexes and polyoxometallate anions can be described in the linear driving force transfer model as one or two parallel processes. It was proposed that the differences observed should be attributed to the different crystal structures of the adsorbents. The compound consisting of a nickel tetramine complex and [HSiW₁₂O₄₀]³⁻ anion displays high selectivity toward ethanol relative to methanol. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 291–298, September–October, 2007.     

DMP与DEP在凝聚相中裂解反应理论研究: 隧道效应与溶剂效应

采用密度泛函理论(DFT)B3LYP方法, 以极化连续模型(PCM)和导体反应场模型(COSMORS)的溶剂模型为基础, 结合反应动力学研究了2,2-二甲氧基丙烷(DMP)与2,2-二乙氧基丙烷(DEP)在凝聚相(溶液相)中的裂解反应. 结果表明, 四元环过渡态裂解反应机理是DMP与DEP裂解反应的主反应通道, 溶剂效应和隧道效应对液相中的裂解反应速率有较大的影响, 而且溶剂效应的影响更显著. 在凝聚相反应理论研究中, 溶剂效应和量子隧道效应都是不能忽略的因素.     

Study of ion exchange selectivity of organic ions by using (31)P NMR spectroscopy

Ion exchange distribution of the phenylphosphoric acid has been studied on various types of chloride form strong base resins as a function of pH at 25 °C, at 0.1 M ionic strength. Equilibrium measurements were supplemented by the study of pH dependence of the ³¹P NMR spectra of the resin-phase phenylphosphate species. Equations were derived to describe the pH dependence of the overall distribution coefficient and the chemical shift of the resin-phase solute species. Experimental data were evaluated by using these model equations and the values of the individual distribution coefficients, ion exchange selectivity coefficients and the resin-phase ³¹P chemical shifts of the mono- and divalent ions have been calculated. Comparison of distribution data of the individual species corroborated the significance of the role of hydrophobic interaction in the selectivity of organic ion exchange processes. A well-defined correlation between the ion exchange selectivity and the resin-phase ³¹P NMR chemical shift data has been pointed out.     

Chronocoulometric flow-injection analysis with solvent polymeric membrane ion sensors

A method to carry out chronocoulometric measurements with solvent polymeric membrane ion sensors in flow-injection systems has been developed. For this, a double potential step was synchronised to the passage of the sample plug through the detector cell. A four-electrode potentiostat with ohmic drop compensation and a new flow-through cell to incorporate the four-electrode and the membrane were developed. A plasticized poly(vinyl chloride) (PVC) membrane containing TBATBP was used and the procedure was applied to the determination of tetraethyl-ammonium. The effect of the electrochemical and flow-injection variables was studied. In the selected conditions, a linear relationship between the quantity of electricity and tetraethyl-ammonium concentration was obtained in the range 5×10⁻⁷-5×10⁻⁵ M. The detection limit was 7×10⁻⁸ M. Good repeatability and between day reproducibility were obtained. The potential application to other quaternary ammonium ions including acetylcholine was also studied.     

4—甲基—7—羟基香豆素的发光特性研究

对比考察了多种溶剂介质中不同浓度４－甲基－７－羟基香豆素溶液的荧光光谱特性，发现其谱形状与峰位不仅随溶剂性质而异，且随浓度而变，在某些氢键溶剂中，激发光谱随浓度有很大变化，且发射光谱间存在某种内在联系。基于溶剂本身的性质及４－甲基－７－羟基香豆素在氢键溶剂中的二聚作用讨论了这种现象，本文还考察了这种香豆素衍生物在滤纸及聚酰胺膜基质上，以Ｐｂ（Ａｃ）２或Ｐｂ（ＮＯ３）２作重原子微扰剂时的室温磷光特性     

V2O5/高硅分子筛的酸性与甲苯气相选择氧化

用固体离子交换法制备了Ｖ２Ｏ５／ＺＳＭ－５和Ｖ２Ｏ５／丝光沸石两类催化剂。通过ＸＲＤ，ＬＲＳ，ＸＰＳ和Ｓｇ测定表征了Ｖ２Ｏ５在分子筛上的分散状态。用吡啶吸附红外光谱法和正丁胺非水溶液回滴法研究了催化剂的表面酸性。用ＥＳＲ研究了甲苯在催化剂上的吸附。结果表明，催化剂的酸性不同，它们吸附甲苯的能力也不同，对甲苯气相选择氧化的活性和选择性也有较大的差异。同时，甲苯选择氧化成苯甲醛的能力还与Ｖ２Ｏ５在分子     

Determination of carbamates and organophosphorus pesticides by SDME–GC in natural water

Water contamination due to the wide variety of pesticides used in agriculture practices is a global environmental pollution problem. Analytical methods with low quantification limits are necessary. The application of a new extraction technique, solvent drop microextraction (SDME), followed by gas chromatography with a nitrogen-phosphorus detector, was assessed for determining carbamates and organophosphorus pesticides in natural water. Experimental parameters which control the performance of SDME such as selection of microextraction solvent, optimization of organic drop volume, effects of sample stirring, salt addition, and, finally, sorption time profiles were studied. Once SDME was optimized, analytical parameters such as linearity (r ²>0.99), precision (<13%), and detection limits (0.2 to 5 μg/L), plus matrix effects were evaluated (no matrix effects were found). SDME is a dynamic technique able to extract pesticides from water in 14 min; the use of organic solvents and water samples for SDME is negligible compared to other extraction techniques.     

Equilibrium isotope effects in aqueous systems. IV. The vapor pressures of NaBr,Nal, KF,Na2SO4, and CaCl2 solutions in H2O and D2O (O to 90°C). Vapor pressures of Na2SO4·10H2O, ·10D2O and CaCl2·2H2O, ·2D2O

Solvent vapor pressure isotope effects have been measured in HOH/DOD between approximately 0 and 90°C on the following electrolyte solutions: NaBr (2, 5, 7, and 9m), NaI (4, 6, 8, and 10m), KF (3, 6, 9, and 12m), Na₂SO₄ (2m and saturated solutions, and hydrated cyrstal), and CaCl₂ (3, 5.5, 8, and 10m, and hydrated crystal). Values of the isotope effects on the various excess thermodynamic properties of solution, including the osmotic and activity coefficients and the excess free energies, enthalpies, and entropies, have been extracted from least-square expressions which fit the VPIE over the entire concentration and temperature range. The results are compared with those obtained for alkali metal chloride solutions (I, II) and literature data where possible. They are discussed briefly in terms of solution structure.