结构描述符正交化及典型相关分析在饱和醇、醚质谱分类中的应用

结构描述符正交化及典型相关分析在饱和醇、醚质谱分类中的应用;饱和醇醚;模式识别;质谱分类变量;块变量;典型相关分析     

Irreversible versus reversible aggregation: mean field theory and experiments

Colloidal aggregation processes arising at different electrolyte concentrations were studied by means of experiments and confronted with theoretical predictions of different kinetic aggregation models. For this purpose, aqueous dispersions of relatively large polystyrene microspheres were chosen as experimental systems. Aggregation was induced by adding KBr electrolyte to the initially stable particle dispersions. During the aggregation processes, the cluster-size distribution was monitored by means of single cluster light scattering. Analyzing the time evolution of the monomer concentration, we found that the processes arising even at moderate electrolyte concentrations cannot be described by pure time-independent irreversible aggregation models. Hence, alternative models such as time-dependent irreversible aggregation and several reversible aggregation models were also tested. The model that considers a time-dependent sticking probability was found to fit the data quite satisfactorily. Nevertheless, the fitted was so slow that it seems not very likely to find such a behavior in real systems. The aggregation-fragmentation models reported in the literature were unable to reproduce the experimental observations. Hence, a more realistic reversible aggregation model was developed. This model accounts also for reenforced or double bonds between the constituent particles. The corresponding fit improved significantly and reached the same quality as the time-dependent model. Moreover, the obtained fitting parameters were in qualitative agreement with the DLVO predictions and so, reversible aggregation seems to be a more reasonable explanation for the experimental data than time-dependent irreversible aggregation. However, no definite statement on the possible secondary bond fragmentation mechanism may be made since both the applied shear stress in the measuring cell and thermal fluctuations can cause weaker bonds to break.     

Comparison of the Use of Washburn's Equation in the Distance-Time and Weight-Time Imbibition Techniques

Two experimental methods are usually employed to study liquid penetration in porous media. One of them is based on the measure of the height of the advance liquid front vs time, and the other one is based on the measure of the weight gained by the porous system due to the liquid penetration vs time. Generally, the experimental data obtained from these techniques are analyzed through Washburn's equation. However, depending on which of them is selected, different conditions, coming from the experimental method, are needed to be taken into account in order to get the correct application of Washburn's equation to the experimental data. Although these conditions are different for each method, we prove in this paper that only if these conditions are considered both techniques are equivalent to analyze imbibition experiments using Washburn's equation. Copyright 2001 Academic Press.     

Oxalato-bridged dinuclear complexes of Cr(III) and Fe(III): synthesis, structure, and magnetism of [(C2H5)4N]4[MM'(ox)(NCS)8] with MM' = CrCr, FeFe, and CrFe

A new series of homo- and heterometallic oxalato-bridged dinuclear compounds of formulas [Et4N]4[MM'(ox)(NCS)8] ([Et4N]+ = [(C2H5)4N]+; ox = C2O4(2-)) with MM' = Cr(III)-Cr(III) (1), Fe(III)-Fe(III) (2), and Cr(III)-Fe(III) (3) is reported. They have been structurally characterized by infrared spectra and single-crystal X-ray diffraction. The three compounds are isostructural and crystallize in the orthorhombic space group Cmca with Z = 8, a = 16.561(8) A, b = 13.481(7) A, and c = 28.168(8) A for 1, a = 16.515(2) A, b = 13.531(1) A, and c = 28.289(4) A for 2, a = 16.664(7) A, b = 13.575(6) A, and c = 28.386(8) A for 3. The structure of 3 is made up of a discrete dinuclear anion [CrFe(ox)(NCS)8]4- and four disordered [Et4N]+ cations, each of them located on special positions. The anion, in a crystallographically imposed C2h symmetry, contains metal cations in distorted octahedral sites. The Cr(ox)Fe group, which is planar within 0.02 A, presents an intramolecular metal-metal distance of 5.43 A. Magnetic susceptibility measurements indicate antiferromagnetic pairwise interactions for 1 and 2 with J = -3.23 and -3.84 cm-1, respectively, and ferromagnetic Cr-Fe coupling with J = 1.10 cm-1 for 3 (J being the parameter of the exchange Hamiltonian H = -2JS1S2). The ESR spectra at different temperatures confirm the magnetic susceptibility data.     

Design of a field flow preconcentration system for cadmium determination in seawater by flow-injection-atomic absorption spectrometry

A field flow preconcentration system (FFPS) for cadmium determination in seawater is described. Seawater samples are collected and preconcentrated in situ by passing them with a peristaltic pump through a minicolumn packed with Amberlite XAD-4 impregnated with the complexing agent 1-(2-pyridylazo)-2-naphthol. Thus, cadmium is complexed, retained, and preconcentrated without the interference of the saline matrix. Minicolumns loaded with cadmium are then returned to the laboratory where they are incorporated into a flow injection system and eluted with a small volume of an ethanolic solution of hydrochloric acid into the nebuliser-burner system of a flame atomic absorption spectrometer. The optimization of FFPS design is presented, and the stability and characteristics of the Cd-loaded minicolumns are studied in detail. The detection limit for Cd in seawater based on an enrichment factor of 1059 was 3.8 ng l(-1). The precision (R.S.D.) obtained for different amounts of cadmium was in the range 4.1-6.5% at the 25-100 ng l(-1) level. Analysis of certified reference materials (SLEW-3 and NASS-5) showed good agreement with the certified value. This procedure was applied to the determination of cadmium in seawater samples from Galicia (Spain).     

Hydrothermal Synthesis and Crystal Structure of a New Supramolecular Channel Framework Based on Cu Complexes and Polyoxovanadate:[Cu(I)(phen)_2]_5[HV_(15)O_(36)(Cl)]_(0.65)[H_3V_(16)O_(38)(Cl)]_(0.35)·2H_2O

1 INTRODUCTION In the past years, polyoxovanadates have attracted extensive interest in solid-state material chemistry owing to the formation of mixed-valence com- pounds that exhibit rich electronic and magnetic properties relevant to catalysis, medicine and ma- terials science[1～4]. The following polyoxovanadates have been found and structurally characterized: [V5O14]3-, [V6O19]8-, [V10O28]6-, [V12O32]4-, [V13- O34]3-, [V15O36]5-, [V15O42]9-, [V17O42]4-, [V18- O42]12-, [V16O38]7…     

Dark and photoinduced interactions between Trolox, a polar-solvent-soluble model for vitamin E, and riboflavin

The aerobic riboflavin (Rf)-sensitized visible-light irradiation of Trolox (TX), a polar-solvent-soluble model for vitamin E, has been studied employing stationary photolysis, polarographic detection of oxygen uptake, stationary and time-resolved fluorescence spectroscopy, and laser flash photolysis. Results indicate that in methanolic solution, no dark complexation exists between Rf and TX. The latter quenches singlet and triplet states of Rf, with rate constants of 6.2 x 10(9) M(-1) s(-1) and 4.7 x 10(9) M(-1) s(-1), respectively. The photodecomposition of Rf, a known process taking place from triplet Rf, has been found to depend on the concentration of dissolved TX: at >/=30 mM very slight Rf photodecomposition occurs due to the massive quenching of excited singlet Rf, while at TX concentrations < or =1 mM triplet Rf is photogenerated and subsequently quenched either by oxygen, giving rise to O(2)((1)Delta(g)), or by TX, yielding semireduced Rf through an electron transfer process. Complementary experiments performed in pure water employing superoxide dismutase and sodium azide inhibition of the oxygen uptake, in coincidence with flash photolysis data, indicate that superoxide anion and singlet molecular oxygen are generated, likely by the reaction of the anion radical from Rf with dissolved oxygen, also yielding neutral, ground state Rf or by energy transfer from triplet Rf to ground-state oxygen, respectively. The final result is that both TX and Rf are photodegraded, likely through oxidation with activated oxygen species. In the absence of oxygen no degradation of TX can be detected, but Rf photodegradation is favoured because Rf regeneration is avoided.     

Automatic on line preconcentration and determination of lead in water by ICP-AES using a TS-microcolumn

A simple, sensitive, low-cost and rapid, flow injection system for the on-line preconcentration of lead by sorption on a microcolumn packed with silica gel funtionalized with methylthiosalicylate (TS-gel) was developped. The metal is directly retained on the sorbent column and subsequently then eluted from it by EDTA. Five variables (sample flow rate, eluent flow rate, eluent concentration, pH and buffer concentration) were considered as factors in the optimization process. Interactions between analytical factors and their optimal levels were investigated using two level factorial and Box-Behnken designs. The optimum conditions established were applied to the determination of lead by flow injection inductively coupled plasma atomic emission spectrometry (FI-ICP-AES). The proposed method has a linear calibration range from 10 to at least 500 ng ml⁻¹ of lead. At a sample frequency of 24 h⁻¹ and a 120 s preconcentration time, the enrichment factor was 41, the detection limit was 15.3 ng ml⁻¹ (S/N=3) and the precision, expressed as relative standard deviation, was 0.9% (at 100 ng ml⁻¹). Validation of the developed method was carried out against electrothermal atomic absorption spectrometry analysis without statistically significant differences between the proposed method and the atomic absorption method.     

Hydrothermal Synthesis and Structure Analysis of Indium Vanadate （InVO4）

1 INTRODUCTION Indium vanadate is a kind of vanadate compounds. There are two crystal phase structures, metastable monocline structure and stable orthogonal structure. Orel, B.[1] and his partners have discovered that V of tetrahedron VO4 has very sensitive energy gap band. Through XPS study of orthogonal InVO4, it is found that its band gap is shorter than those of InNbO4 and InTaO4, and its band-gap energy is 2.0 eV[4]. Ortho- gonal InVO4 can act during the range from short- wav…     

Optimization of the separation of a group of triazine herbicides by micellar capillary electrophoresis using experimental design and artificial neural networks

The micellar electrokinetic chromatography separation of a group of triazine compounds was optimized using a combination of experimental design (ED) and artificial neural network (ANN). Different variables affecting separation were selected and used as input in the ANN. A chromatographic exponential function (CEF) combining resolution and separation time was used as output to obtain optimal separation conditions. An optimized buffer (19.3 mM sodium borate, 15.4 mM disodium hydrogen phosphate, 28.4 mM SDS, pH 9.45, and 7.5% 1-propanol) provides the best separation with regard to resolution and separation time. Besides, an analysis of variance (ANOVA) approach of the MEKC separation, using the same variables, was developed, and the best capability of the combination of ED-ANN for the optimization of the analytical methodology was demonstrated by comparing the results obtained from both approaches. In order to validate the proposed method, the different analytical parameters as repeatability and day-to-day precision were calculated. Finally, the optimized method was applied to the determination of these compounds in spiked and nonspiked ground water samples.