Eduard Burtscher

High-performance liquid chromatographic elution behaviour of alcohols, aldehydes, ketones, organic acids and carbohydrates on a strong cation-exchange stationary phase

Abstract The high-performance liquid chromatographic separation of alcohols, aldehydes, ketones, carboxylic acids and carbohydrates on a polystyrene-based strong cation-exchange resin is described. The column temperature was found to be a very important parameter for optimizing separations of these substances. The effect of different functional groups on the elution behaviour is discussed.

Anthraquinones as mediators for the indirect cathodic reduction of dispersed organic dyestuffs

Abstract 9,10-Anthraquinone-2-sulfonic acid Na-salt (AQS2), 9,10-anthraquinone-1,5-disulfonic Na-salt (AQDS1,5) and 1,4-dihydroxy-9,10-anthraquinone (DHAQ1,4) were investigated as to their ability to act as mediators for indirect electrochemical reduction of dispersed organic dyestuffs. A characterisation of the reducing efficiency was obtained from CV-experiments when comparing the cathodic current maxima of the AQ solution containing the dyestuff with the cathodic peak current without reducible vat dye. Voltammograms in a flow cell show that the limiting current density is dependent mainly on the diffusion transport of the AQ, while the addition of reducible dispersed dyestuff is of minor influence. Spectroelectrochemical experiments performed with 9,10-anthraquinone-1,5-disulfonic Na-salt in presence of Vat Yellow 1 permit a photometric observation of the coupled redox reactions.

Separation of phenols, phenolic aldehydes, ketones and acids by high-performance liquid chromatography

Abstract The high-performance liquid chromatographic separation of phenols, benzaldehydes, acetophenones, benzoic and cinnamic acids as well as some related compounds is described. An octadecyl silica column was used with a 0.01 M phosphate buffer-acetonitrile gradient as mobile phase. The retention times of the substances investigated depend on their polarity. An elution order depending on the basic functional groups and the substituents has been established.

Chromatographic analysis of biomass reaction products produced by hydrothermolysis of poplar wood

Abstract Poplar wood was treated under hydrothermal conditions at various temperatures the wide spectrum of reaction products was analysed by different liquid chromatographic methods. Low-molecular-weight compounds were investigated by means of high-performance liquid chromatography. Sugars and sugar decomposition products were analysed using a cation-exchange column; the separation of lignin degradation products was carried out by reversed-phase chromatography with gradient elution. The high-molecular-weight components were characterized by gel permeation chromatography (GPC). Oligomeric sugars were eluted from a gel column with water as the eluent. The molecular weight distribution of degraded lignin was obtained by GPC with a mixture of dioxane—water as the eluent. The application of the methods described does not require a time-consuming sample preparation. Therefore a rapid analysis and quantification of the reaction products is possible. This allows the investigation of the course of reaction and the calculation of the mass balance. In addition, the optimum process parameters can be evaluated from kinetic studies of the hydrothermolysis reaction.

Indirect Electrochemical Reduction of Dispersed Indigo Dyestuff

Iron-triethanolamine complexes are well suited for the indirect reduction of dispersed dyestuffs, e.g., finely dispersed indigo in a dyebath. Experiments to develop basic data for the scale-up of an electrochemical cell usable for the indirect reduction of indigo, vat dyes, and sulfur dyes are described. Planar electrodes show that the current density at the cathode is limited by diffusion controlled transport phenomena in the mediator system. The characterization of the iron triethanolamine mediator system is performed by reduction experiments in a divided flow cell with parallel geometry. An optimization of this cell type was achieved with three-dimensional flow through electrodes, leading to high specific electrode areas and a good space/time yield with the investigated electrochemical system. The characterization of the different cell types was performed with electrolysis experiments using the mediator alone and in the presence of dispersed indigo dyestuff

The redox-catalysed reduction of dispersed organic compounds: Investigations on the electrochemical reduction of insoluble organic compounds in aqueous systems

Abstract The indirect reduction of insoluble dispersed organic compounds (e.g. dye systems) is described. Using cyclic voltammetry (CV), it is shown that aqueous alkaline iron-amine complexes reach cathodic current peak potentials of over −1000mV. Therefore such complexes are very well suited to act as mediators for the reduction of the compounds investigated, such as dye pigments, with anthrachinoid, indigoid and disulphidic molecular structures, which have markedly less negative reduction potentials. The analysis of the CV experiments gives valuable information concerning the reaction rates (described by enhancement factors), the concentration behaviour and the type of mediator system. The experiments demonstrate a practical method of evaluating suitable mediator systems for the indirect electrochemical reduction of dyestuff molecules. In the technical dyeing processes using vat dyes, indigo and sulphur dyes, the reduction step is a main reaction in the application on cellulosic fibres, e.g. cotton.

Alkali-stable iron complexes as mediators for the electrochemical reduction of dispersed organic dyestuffs

Several complexones and amino compounds have been investigated as to their ability to form alkali-stable coordination compounds with iron, which can be used as mediators for the indirect electrochemical reduction of dispersed organic dyestuffs with different structures. A characterisation of the reducing efficiency can be obtained when the cathodic current maxima of the mediator solution containing the dyestuff is compared with the cathodic peak current without the reducible vat dye.

Chromatographic behaviour of aromatic compounds on Sephadex LH gels : Calibration of gel columns for determination of molecular weight distributions

Abstract The chromatographic behaviour of phenols, phenolic acids, aromatic carbonylic compounds and cinnamic compounds on Sephadex LH gels is determined, and the dependence of the elution characteristics on the composition of the solvent, dioxane-water are reported. The results show that a dioxane-water composition of 7:3 causes the distribution coefficients to lie in a narrow range, in spite of the chemically different character of the investigated compounds. In pure dioxane strong adsorption effects are observed. In water-dioxane mixtures, however, partition effects occur when the water content is considerably higher than 30%. The results are used to design a gel chromatographic system for molecular weight determination using Sephadex LH gels and dioxane-water as eluent.

Dyeing Behavior of Indigo Reduced by Indirect Electrolysis

Dispersed indigo dyestuff can be reduced by indirect electrolysis using an iron (II)-triethanolamine complex. The iron (III) form of the complex can be transformed to the iron (II) form by cathodic reduction, thus leading to a regenerable reducing agent. Electrochemically reduced indigo is tested in laboratory scale dyeing experiments, and the results of different reduction conditions in the dyebath are discussed. The influence of the concentration of the complex-system on the build-up of color depth and shade with increasing number of dips is discussed and compared with samples of the standard dyeing procedure using sodium dithionite as reducing agent. The results of the latter conventional process show that the dyestuff in the dyebath behaves in a manner similar to that when a regenerable Fe(II)-complex is used as the reducing agent.

Multi-cathode cell with flow-through electrodes for the production of iron(II)-triethanolamine complexes

Nonregenerable reducing agents used in dye houses for the application of indigo, vat dyes and sulfur dyes can be substituted by indirect cathodic reduction techniques. An electrochemical cell for the indirect cathodic reduction of dispersed indigo dyestuff using an alkaline solution of the Fe(iii/ii)-triethanolamine complex as redox mediator was constructed and tested. The cell is built up as divided cell (cathode area 5–10m2, catholyte volume 12L, anolyte volume 1.5L) with several three dimensional cathode units (up to 10) in the same cathode compartment. The cathodes were connected to a common anode and to separately adjustable power supplies. The catholyte was circulated through the porous cathode units parallel to the current direction. Two different electrode materials (copper and stainless steel) and cathode constructions were tested, resulting in an optimized cell construction. The electrochemical cell was characterized by a series of batch electrolysis experiments. Results are given dealing with the cell voltage drop in the cathode, the product yield and the current efficiency at different current densities and cell current. After an optimization step the current efficiency reaches 70–80% at 2 A m–2 current density and 7.8×10–3moldm−3 Fe(ii)-complex. The cell current is 10A.