Electrochemistry of capillary systems with narrow pores. I. Overview

In capillary systems with narrow pores the Helmholtz electrochemical double layer located at the pore wall extends over the entire cross section of the pores. It loses its character as the “charge on the wall”. It will be shown that not only the electrokinetic phenomena but also the electrical conductivity and the dialysis potential of membranes with narrow pores can be understood from the same point of view, namely: the electrolyte solution in the pores of a membrane with narrow pores is considered to be an approximately homogeneous solution in contact with immobilised charges located at the pore wall. In this case the electrochemical equations contain the fixed ion concentration as a parameter instead of the ζ potential. This makes it possible to describe quantitatively to a good approximation data on the electroosmosis, the electrical conductivity, the streaming potential and the dialysis potential taken from the literature, as well as results of our own measurements, by using a single membrane constant.     

Photoelectron spectra of vinyl- and 1-alkynylgermanes and stannanes

Primary vinylic and acetylenic germanes and stannanes, synthesized by a chemoselective reduction of the corresponding trichloro derivatives, were investigated by ab initio quantum chemical methods and photoelectron spectroscopy. In particular, the PE spectra display very well-resolved bands which show the increasing destabilizing effect of 14 group heteroatom α-substitution of double or triple carbon–carbon bonds.     

Multicomponent analysis in luminescence spectroscopy

Multicomponent analysis of absorption spectra (infrared or electronic spectra) by factor analysis is a suitable method to use. The algorithm of factor analysis is now available for luminescence spectroscopy. The first possibility, as in absorption spectroscopy, is to determine pure components emission spectra for a unique set of spectra of mixtures in overdetermined conditions. On the other hand, it is also possible to extract pure components emission and excitation spectra of the only data corresponding to the 3D fluorescent spectrum of a single mixture. The results are evaluated in respect to noise level and concentrations ratio on both simulated and real spectra.     

Determination and fractionation of sulphur in a contaminated dredged sediment

Conversion of sulphur compounds in reduced, contaminated sediments that are brought in upland conditions may largely affect the potential mobility of heavy metal contaminants. We applied selected methods for the determination of total sulphur and sulphur fractions in a contaminated sediment in the reduced state and after gradual drying and oxidation during 1 month. Dry ashing, followed by ion chromatographic detection, was reliable for the determination of total sulphur. Good recoveries were obtained in both reference samples and spiked samples. Total sulphur was 14.5±0.6 g kg⁻¹ relative to dry sediment. Wet chemical methods that involve the determination of acid-volatile, Zn–HCl-reducible, chromium-reducible, acetone-soluble and HI-reducible sulphur were used to estimate specific sulphur forms. Results for acetone-soluble sulphur were to high and not consistent with results for other fractions. Major part of sulphur in the sediment (90%) was inorganic. Sulphides were converted partially to sulphate and to intermediary oxidised sulphur compounds upon oxidation of the sediment. The results suggested that the intermediary oxidised sulphur pool in the reduced sediment (2.5 g kg⁻¹) mainly consisted of pyrite, that was not converted during drying and oxidation. No significant changes in organic sulphur were detected.     

New methods for spectrometric peak purity analysis in chromatography

Simple methods for peak purity analysis in chromatography are proposed for accurately assaying the chromatographic or electrophoretic process by spectroscopy. With these methods, the purity at each point of a chromatographic peak containing an unknown type and number of components can be detected and visualized. The ‘absorbance (A) diagram' is constructed by plotting the absorbance values of different wavelengths against each other. When only straight lines are obtained for different wavelength combinations, only one component was detected in the corresponding peak. Bent curves in the A diagrams mean that at least two components were registered. Straight lines in the absorbance difference quotient (ADQ) diagrams indicate that two components occur in the corresponding peak. Bent curves signify that at least three components were registered. The new methods are demonstrated using the HPLC technique for the separation of chlorogenic acid and epicatechin. Integral A and ADQ diagrams and the corresponding mean diagrams complete the new concept.     

Electrochemistry of capillary systems with narrow pores III. Electrical conductivity

The extension of the Teorell–Meyer–Sievers theory of the dialysis potential to a general theory of capillary systems with narrow pores outlined in Part I of this series of publications has been applied to electroosmotic phenomena in Part II. In this Part, the electrical conductivity, including the electrical convection conductivity, will be treated in terms of the new theory. The corresponding equations already referred to in Part I are derived. In addition, results of measurements of the electrical conductivity of collodion membranes with graded porosity and graded electrochemical activity in aqueous KCl solutions of different concentrations are reported. They are used to test the new theory. It will be shown that it is possible to determine the fixed ion concentration A of the membranes by using electrical conductivity data. The theory predicts that the value of A should be identical with the `selectivity constant' of the Meyer–Sievers theory of the dialysis potential. This prediction will be checked in Part IV of this series of contributions.     

Electrochemistry of capillary systems with narrow pores. IV. Dialysis potentials

The dialysis potentials of different collodion membranes with graded pore sizes and electrochemical activities have been measured in dilute aqueous KCl solutions as functions of concentration. It is possible to predict the value of the diffusion potential within a few millivolts on the basis of electrical conductivity data obtained with the same membranes. In general, the measured values are lower than those calculated. It is assumed that this difference is caused by the membranes having a distribution of pore sizes.     

Separation of serum proteins with uncoupled microsphere particles in a stirred cell

Submicron microspheres were used directly without ligand coupling for the batch and continuous separations of proteins. In the batch experiments for separating BSA (bovine serum albumin) from BHb (bovine hemoglobin), introducing both hydrophobic effects for BSA and electrostatic repulsion for BHb (and vice versa) was required for high selectivity, and microspheres with low number density of surface groups were advantageous. For the continuous experiments, the utilization of a stirred cell was successful, where the microspheres were in the form of latex with good dispersion of particles. The flow rate without a pump was 0.5–1.3 ml min⁻¹, and the ratio of BSA and BHb was varied. In the experiments for eliminating BHb from BSA, elution curves of BHb corresponded to the single component breakthrough curves, while those for BSA did not. The latter is believed to be due to the interference by BHb in the adsorption of BSA.     

Heteroatom derivatives of indene: V. Vibrational spectra of benzimidazole

Infrared and Raman measurements for benzimidazole are presented and discussed, including its argon-matrix infrared spectrum. To assist in the assignment, benzimidazole's harmonic force fields for the 321G* and 631G* levels were scaled by scaled factors derived by fitting the respective computed force fields of other indene derivatives to previously reported experimental vibrational frequencies. Comparison to the best set of experimental wavenumbers, usually taken from the matrix, shows mean 321G* and 631G* deviations of 7.0 and 5.8 cm⁻¹ for the planar modes, and 14.0 and 6.8 cm⁻¹ for the nonplanar modes, respectively, with much of the error residing in imino-hydrogen group modes. Standard entropies are derived with the matrix wavenumbers and the methods of statistical mechanics. An attempt to determine standard entropies by calorimetric methods was unsuccessful. The triple-point temperature T_tp and enthalpy of fusion Δ¹_crH_m only are reported.     

Electrochemistry of capillary systems with narrow pores. II. Electroosmosis

Manegold and Solf have reported systematic deviations of the electroosmotic properties of collodion membranes with narrow pores from predictions based on the Helmholtz–Smoluchowski model. To interpret the electroosmotic data quantitatively it is necessary to replace the assumption of the Helmholtz–Smoluchowski model that the thickness of the electric double layer is small compared with the pore radius by a new assumption. We have assumed that the counter ions are distributed homogeneously in the pore fluid. In Part I of this series of contributions, equations have been given describing the electroosmotic properties of a membrane with narrow pores based on the new assumption. These equations are derived here in detail and are applied to an analysis of the experimental data given by Manegold and Solf.     

Multielemental speciation of As, Se, Sb and Te by HPLC-ICP-MS

An anion exchange HPLC-ICP-MS procedure allowing the simultaneous multielemental speciation analysis of arsenic, selenium, antimony and tellurium has been developed. Four arsenic species (As^III, As^V, monomethylarsonic acid and dimethylarsinic acid), two selenium species (Se^IV and Se^VI) may be determined in a single run as well as one antimony (Sb^V) and one tellurium species (Te^VI). Alternatively Sb and/or Te may be used as internal standards for As and Se speciation studies. Optimisation of ICP-MS conditions led to satisfactory relative (0.01 (Sb^V) to 1.8 (Se^VI) ng ml⁻¹) and absolute detection limits (1–180 pg). Reproducibility ranged from 3.1 to 5.6% and the linearity was verified in the 0–200 ng ml⁻¹ range.     

Improvement of poly(amphiphilic pyrrole) enzyme electrodes via the incorporation of synthetic laponite-clay-nanoparticles

The electropolymerization of an enzyme-amphiphilic pyrrole ammonium-laponite nanoparticles mixture preadsorbed on the electrode surface provides the simultaneous immobilization of the enzyme and the hydrophilic laponite-clay-nanoparticles in a functionalized polypyrrole film. The presence of incorporated laponite particles within the electrogenerated polymer induces a strong improvement of the analytical performances (I_max and sensitivity) of amperometric biosensors based on polyphenol oxidase. These beneficial effects have been attributed to a marked enhancement of the apparent specific activity of the immobilized enzyme (from 0.21 to 0.85% of the specific activity of the free enzyme), the permeability of the host polymer being unchanged. This strategy of biosensor performance improvement was tested with cholesterol oxidase as an enzyme model. The presence of laponite additive in the poly(amphiphilic pyrrole) host matrix induces a similar enhancement of sensitivity and I_max for cholesterol biosensing as well as a large improvement of the storage stability of the polypyrrole-cholesterol oxidase electrode.     

Analysis of volatiles emitted by potato plants by means of a Colorado beetle electroantennographic detector

An electroantennographic detector based on the antenna of the Colorado potato beetle (Leptinotarsa decemlineata Say, 1824) was used to investigate volatile organic compounds emitted by injured potato plants (Solanum tuberosum L., 1753). Samples were collected on charcoal traps using the CLSA method. Analyses were performed with a GC-EAD-FID setup as well as a GC-MS system. The experiments revealed that several groups of compounds are perceptible to the Colorado potato beetle. The ability of the Colorado potato beetle to detect green leaf odours (e.g. (Z)-3-hexen-1-ol and (E)-2-hexenal), linalool and some terpenes has been noticed before [Visser et al., J. Chem. Ecol. 5 (1979) 13]. In this work the presence of (Z)-3-hexen-1-ol, (E)-2-hexenal and linalool in the potato odour could be confirmed. Moreover, β-myrcene, benzeneethanol, and several sesquiterpenes (e.g. caryophyllene and germacrene-D) were identified. The GC-EAD experiments reveal that apart from the green leaf odours and linalool prominent reactions of the Colorado bettle antenna are induced by benzeneethanol and the sesquiterpene fraction.     

Newly designed flow field-flow fractionation channel for macromolecules and particles in the submicrometer and micrometer range

The flow field-flow fractionation (FIFFF) technique is a promising method for separating and analysing particles and large size macromolecules from a few nanometers to approximately 50 μm. A new fractionation channel is described featuring well defined flow conditions even for low channel heights with convenient assembling and operations features. The application of the new flow field-flow fractionation channel is proved by the analysis of pigments and other small particles of technical interest in the submicrometer range. The experimental results including multimodal size distributions are presented and discussed.     

Operationally defined extraction procedures for soil and sediment analysis: II. Certified reference materials

Single or sequential extraction procedures are often used for soil and sediment studies to determine forms or phases of elements (e.g. `bioavailable' forms of elements). The significance of the analytical results is highly dependent on the extraction procedures used, owing to the `operationally defined' character of these schemes which requires the adoption of standardized protocols. The first part of the present review discusses the aspects of standardization of leaching and extraction schemes as applied to environmental analysis. This second part focuses on the validation aspects of such procedures and describes the preparation and certification of soil and sediment reference materials certified for their extractable trace element contents, following standardized single and sequential extraction procedures.     

Competitive hydrogenation in alkene–alkyne–diene systems with palladium and platinum catalysts

Competitive hydrogenation of alkene, alkyne and diene substrates (C₆–C₈) over palladium and platinum catalysts were studied at 20°C and atmospheric pressure. Selectivities of these reactions were determined and the substrates relative adsorption coefficients calculated. It was found that hydrogenations of alkynic and dienic substrates were preferred in alkyne–alkene and diene–alkene systems, respectively. In these systems palladium catalyst selectivity was higher than selectivity of the platinum catalyst, due to higher relative adsorption coefficients of corresponding substrate couples on the palladium catalyst.     

Seventeen new 14- and 15-crown-formazans: their synthesis and evaluation in spectrophotometric determination of lithium

A number of new crown-formazans with 14 and 15 membered rings have been synthesized, characterized and investigated as selective spectrophotometric chelating agents for lithium. The effect of sodium ion concentration on the background lithium signal was studied. A comparative study for the sensitivity of these new crown-formazans in spectrophotometric determinations was studied and compared with those reported previously. The three new 14- and 15-crown-formazans 4a–c containing the pyridyl N-oxide at the formazyl carbon showed the highest selectivity to lithium determination in the presence of sodium ion.     

Application of an artificial neural network (ANN) and piezoelectric chemical sensor array for identification of volatile organic compounds

A piezoelectric chemical sensor array was developed using four quartz crystals. Gas chromatographic stationary phases were used as sensing materials and the array was connected to an artificial neural network (ANN). The application of the ANN method proved to be particularly advantageous if the measured property (mass, concentration, etc.) should not be connected exactly to the signal of the transducers of the piezoelectric sensor. The optimum structure of neural network was determined by a trial and error method. Different structures were tried with several neurons in the hidden layer and the total error was calculated. The optimum values of primary weight factors, learning rate (η=0.15), momentum term (μ=0.9), and the sigmoid parameter (β=1) were determined. Finally, three hidden neurons and 900 training cycles were applied. After the teaching process the network was used for identification of taught analytes (acetone, benzene, chloroform, pentane). Mixtures of organic compounds were also analysed and the ANN method proved to be a reliable way of differentiating the sensing materials and identifying the volatile compounds.     

Chiral calixarene derived from resorcinol. Part 4: Diastereoselective closure of the oxazine ring

A method for the preparation of a single diastereomer of the oxazine derivative of calixresorc[4]arene 3 has been developed. Lewis acids were employed for opening of the oxazine ring.     

A review of the main factors influencing the FT-IR-PLS abilities exemplified with petrochemical qualimetric applications

Quality control usually involves monitoring several variables directly related with industrial necessities using univariate tests. One powerful alternative is to link multivariate analytical techniques and multivariate chemometrics. In this way, Fourier Transform Infrared spectroscopy and Partial Least Squares regression are used to discuss and review several advantages and drawbacks encountered in using such combination in industrial facilities. Typical drawbacks are selection of data pretreatment, errors in reference methods, selection of calibration and validation sets and model-aging. This review is exemplified with petrochemical applications although other fields are also considered (mainly when dealing with data pretreatment).