Biamperometric neutralisation titrations in non-aqueous solvents applying tin electrode pair for the end-point detection

Summary Tertiary amines and salts of organic acids in acetic anhydride with 5% of acetic acid were titrated applying a biamperometric indicating system consisting of a polarised or unpolarised pair of tin electrodes by means of 0.1 N perchloric acid in glacial acetic acid. Amounts of 15.4–29.8 mg were analysed with average deviations of <0.6%, the results obtained being in a good agreement with those of potentiometry. The biamperometric end-point detection using an indicating system of polarised pair of tin electrodes can be applied for coulometric determinations of these bases with satisfying accuracy. By means of anodic generation of hydrogen ions in the presence of hydroquinone amounts of 0.5–1.0 mg were titrated with average deviations of < 1.3%. The results obtained were compared with those obtained of catalytic thermometric and photometric titrations.

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Biamperometrische Neutralisationstitrationen in nichtwärigen Lösungsmitteln unter Anwendung eines Zinn-Elektrodenpaares als Indicatorsystem

Zusammenfassung Tertiäre Amine und Salze organischer Säuren werden in Acetanhydrid mit 5% Essigsäure durch Titration mit einer 0,1 N Lösung von Perchlorsäure in Essigsäure bestimmt. Das verwendete biamperometrische Indicatorsystem besteht aus einem Paar polarisierter oder nichtpolarisierter Zinnelektroden. Mengen von 15,4–29,8 mg wurden mit einer mittleren Abweichung von <0,6% analysiert. Die Ergebnisse stimmen gut mit denen von potentiometrischen Titrationen überein. Die biamperometrische Endpunkttechnik mit polarisierten Zinnelektroden kann für coulometrische Bestimmungen dieser Basen mit zufriedenstellender Genauigkeit benutzt werden. Durch anodische Erzeugung von Wasserstoffionen in Gegenwart von Hydrochinon wurden Mengen von 0,5–1,0 mg mit einer mittleren Abweichung von < 1,3% titriert. Die Ergebnisse wurden mit denen von katalytisch-thermometrischen und photometrischen Titrationen verglichen.

     

The enhancement of acidity in non-aqueous solvents

Summary The acid strength of short-chain carboxylic acids in acetonitrile and acrylonitrile can, by addition of anhydrous alkaline earth perchlorates, be enhanced sufficiently to permit titration of the acid with a tertiary amine in the presence of acid anhydride. This salt effect has been studied by means of potentiometric and automatic thermometric titrations and two distinct mechanisms are thought to be involved: a metathetical reaction at low salt concentrations and a proton desolvation effect at high salt concentrations. High-resolution infra-red spectroscopy has been used to assess the extent of sol vent-cation interaction in acetonitrile. Several equations are used to describe the probable interactions taking place in such salt enhancement phenomena.

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Steigerung der Acidität in nichtwärigen Lösungsmitteln

Zusammenfassung Der Säuregrad von kurzkettigen Carbonsäuren in Acetonitril und Acrylnitril kann durch Hinzufügen von wasserfreien Perchloraten der Erdalkalien genügend gesteigert werden, um bei Vorhandensein von Säureanhydrid eine Titration der. Säure mit einem tertiären Amin zu ermöglichen. Dieser Salzeffekt wurde mit Hilfe von potentiometrischen und automatischen thermometrischen Titrationen untersucht, und es wird angenommen, daß dabei zwei verschiedene Vorgänge eine Rolle spielen: eine Austauschreaktion bei schwachen und ein Desolvatationseffekt bei hohen Salzkonzentrationen. Zur Beurteilung des Ausmaßes der Wechselwirkung zwischen Lösung und Kation in Acetonitril wurde die Infrarot-Spektroskopie mit hoher Auflösung benutzt. Die wahrscheinlich stattfindenden Reaktionsvorgänge werden anhand verschiedener Gleichungen beschrieben.

Lecture presented at Euroanalysis I Conference, 28.8.–1. 9. 1972 in Heidelberg, Germany.     

The non-aqueous titration of benzotrifuroxan (BTF)

Summary BTF can be titrated potentiometrically as an acid with tetrabutylammonium hydroxide in DMF, DMSO, acetone, pyridine, or TMG. The solvent of choice is DMF which yields the steepest titration curve and the lowest standard deviation. The equivalent weight of BTF is dependent on the solvent used, indicating a strong interaction with the solvent. In DMF the equivalent weight of BTF is 151.3, corresponding to 1.67 equivalents per mole.

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Titration von Benzotrifuroxan (BTF) in nichtwäßriger Lösung

Zusammenfassung F kann potentiometrisch als Säure mit Tetrabutylammoniumhydroxid in Dimethylformamid, Dimethylsulfoxid, Aceton, Pyridin oder Tetramethylguanidin titriert werden. Dimethylformamid ist am vorteilhaftesten, da es die steilste Titrationskurve und die niedrigste Standardabweichung (0,43%) bietet. Das Äquivalentgewicht von BTF hängt von dem gewählten Lösungsmittel ab. Dies deutet auf eine beträchtliche Wechselwirkung mit dem Lösungsmittel hin. In Dimethylformamid beträgt das Äquivalentgewicht 151,3, entsprechend 1,67 Äquivalenten pro Mol.

     

Dichlorohydantoin and dibromohydantoin as new oxidimetric titrants in non-aqueous media

Two new oxidimetric titrants, dichlorohydantoin and dibromohydantoin are introduced for use in acetic acid medium, and have been applied to direct potentiometric titration of AS(III), Sb(III), Sn(II), Fe(II), Tl(I), Fe(CN)(6)(4-), I(-), SCN(-), hydrazine, phenylhydrazine, semicarbazide, hydroquinone, oxine and Reinecke's salt, in aqueous acetic acid medium.     

Indicators in non-aqueous cerimetric titrations of thioureas and xanthates

The use of some chemical indicators in the non-aqueous cerimetric determination of thioureas and xanthates in acetonitrile medium is described.     

Anomalies in Faradaic rectification polarography of aromatic compounds in non-aqueous solvents

The electrode reaction of p-dicyanobenzene^O/? in N,N-dimethylformamide is studied with the aid of the galvanostatic double pulse (GDP) method and faradaic rectification (FR) polarography. The results of the GDP measurements obey the theoretical requirements in all aspects. Conversely, the FR polarogram can be fitted with the theoretical polarograms only in the potential range ?-50 mV vs. the reversible half-wave potential of this electrode. Furthermore, the most suitable k⁰ values used in this curve-fit analysis depends on the frequency of ac input and differ greatly from the value determined by the GDP method. Attention is called to the fact that the p-dicyanobenzene^0/? system is just one of the 16 redox systems of aromatic compounds which show this type of behaviour in FR and GDP experiments. Their kinetic parameters are also tabulated, with some comments on the anomalies in FR polarography.     

Cerimetry in non-aqueous media

Summary It was found that ceric oxalate is an intermediate product in the oxidation of oxalic acid by ammonium hexanitrato cerate in solvents such as acetonitrile, and a mixture of acetonitrile and glacial acetic acid. Conditions for the formation of ceric oxalate and its decomposition into carbon dioxide and cerous oxalate have been studied. An analytical method for the estimation of oxalic acid in non-aqueous media has been evolved based on this reaction.

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Zusammenfassung Es wurde festgestellt, daß bei der Oxydation von Oxalsäure mit Ammoniumhexanitratocerat(IV) in Acetonitril oder einem Gemisch von Acetonitril und Essigsäure Cer(IV)-oxalat als Zwischenprodukt auftritt. Die Bedingungen für die Bildung von Cer(IV)-oxalat und seine Zersetzung zu CO₂ und Cer(III)-oxalat wurden untersucht. Ein Verfahren zur Oxalsäurebestimmung in nichtwäßrigem Medium wurde ausgearbeitet.

     

Foams from non-aqueous systems

The multi-phase approach to clarify the fundamentals of the stability of foams from non-aqueous liquids has been further developed. The two-phase liquid/liquid crystal line of attack for the liquid oil variety has been extended to foams stabilized by solid particles, in turn leading to progress in the fundamental science of solid metal foams and plastic foams.     

Stability of non-aqueous dispersions

Ohne Zusammenfassung     

Stability of non-aqueous dispersions

Summary Theoretical values of the magnitude and location of potential energy maxima, of stability ratio and of half-life for colloidal dispersions in hydrocarbon media have been computed from the DLVO theory of colloid stability for spherical particles of radii 200–10,000 Å, and for a range of surface potential (5–80 mV) andHamaker constant (5×10^–13–1×10^–11 erg). The stability relationships show a marked dependence on particle size but are relatively insensitive to the value of theHamaker constant. The results may with some confidence be used to predict the stability of a dispersion in a hydrocarbon medium.

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Zusammenfassung Die Maxima der potentiellen Energie, die Stabilitätsverhältnisse und die Halbwertszeiten von kolloiden Dispersionen in Kohlenwasserstoffen wurden nach der Theorie vonDerjaguin, Landau, Verwey undOverbeek für kugelige Teilchen mit Radien von 200 bis 10000 Å und für Oberflächenpotentiale von 5 bis 80 mV berechnet. Für dieHamaker-Konstante wurden Werte von 5×10^–13 bis 1×10^–11 eingesetzt. Die Stabilität zeigt eine deutliche Abhängigkeit von der Partikelgröße, wird aber von der Größe derHamaker-Konstanten nur wenig beeinflußt.Die Resultate können zu Voraussagen über die Stabilität von Dispersionen in Kohlenwasserstoffen herangezogen werden.

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With 5 figures     

Novel combination of non-aqueous capillary electrophoresis and multivariate curve resolution-alternating least squares to determine phenolic acids in virgin olive oil

This paper presents the development of a non-aqueous capillary electrophoresis method coupled to UV detection combined with multivariate curve resolution-alternating least-squares (MCR-ALS) to carry out the resolution and quantitation of a mixture of six phenolic acids in virgin olive oil samples. p-Coumaric, caffeic, ferulic, 3,4-dihydroxyphenylacetic, vanillic and 4-hydroxyphenilacetic acids have been the analytes under study. All of them present different absorption spectra and overlapped time profiles with the olive oil matrix interferences and between them. The modeling strategy involves the building of a single MCR-ALS model composed of matrices augmented in the temporal mode, namely spectra remain invariant while time profiles may change from sample to sample. So MCR-ALS was used to cope with the coeluting interferences, on accounting the second order advantage inherent to this algorithm which, in addition, is able to handle data sets deviating from trilinearity, like the data herein analyzed. The method was firstly applied to resolve standard mixtures of the analytes randomly prepared in 1-propanol and, secondly, in real virgin olive oil samples, getting recovery values near to 100% in all cases. The importance and novelty of this methodology relies on the combination of non-aqueous capillary electrophoresis second-order data and MCR-ALS algorithm which allows performing the resolution of these compounds simplifying the previous sample pretreatment stages.     

Electrostatic stabilization in non-aqueous media

This paper discusses electrostatic stabilization of dispersions in non-aqueous media. It begins with the theory of repulsion, with particular attention to the roles of the dielectric constant and ionic strength of the liquid medium. Results for flat plates and spheres are compared. Methods are reviewed to measure the dielectric and electric parameters in non-aqueous media, in conjunction with procedures to determine the mechanical properties of electrostatically stabilized, concentrated suspensions.From theoretical considerations it appears that the extent of the electrostatic stabilization in non-aqueous media is extremely sensitive to the dielectric constant ϵ of the liquid, affecting stability in particular through the degree of dissociation of the stabilizing electrolyte. It is essential that, besides the presence of charge on the particles, there also are certain levels of ions in the solution to ensure a sufficient force of repulsion. It is expedient to distinguish three regimes of ϵ: (a) ϵ ⩾ 11, the (semi-)polar range, where systems can be charge-stabilized more or less as in aqueous systems, (b) the low-polar regime (5 ⩽ ϵ ⩽ 11), where electrostatic stabilization is possible provided some dissociated electrolyte is present and (c) the apolar range (ϵ⩽ 5), where screening is exclusively determined by the polarization of the solvent, and where electrostatic stabilization may be more problematic.Concentrated dispersions of solids in liquid nonionic carriers with dodecyl-benzene sulphonic acid (HDBS) as the stabilizer arc good models for the ‘low polar’ category, as detailed experimental data illustrate. In such media HDBS creates a ζ-potential, and enhances the dielectric constant and the ionic strength of the continuous phase. Especially when attraction between suspended salt particles in liquid nonionics is weak, electrostatic stabilization is easily achieved. This is particularly noticed in the rheology of the concentrated suspensions of some salts.     

非水毛细管电泳研究进展

毛细管电泳经过30多年的迅速发展,已经形成多模式操作、可用于多个领域的重要分离分析技术.多年来,大部分科研工作者的注意力都集中在水系毛细管电泳的研究上,而对非水体系的毛细管电泳研究重视不够.Jorgenson等[1]在1984年就已经报道了以乙腈为介质的非水毛细管电泳(NACE),近年来,更多的科学家才把他们的研究重心移向非水毛细管研究.下面就一些进展作简要综述.     

Specific-ion effects in non-aqueous systems

It is widely acknowledged that specific-ion effects are ubiquitous in aqueous systems and undoubtedly are essential to the fundamental processes of life, although a deep fundamental understanding of specific-ion effects remains an important challenge. Specific-ion effects in non-aqueous solvents are known but have attracted far less attention, yet knowledge of specific-ion effects in non-aqueous systems is likely to provide important information for guiding, evaluating and testing our theories of specific-ion effects. Here, the literature on specific-ion effects in non-aqueous solvents is surveyed with a view to determining if the Hofmeister series or lyotropic series so universally observed in aqueous systems is widely evident in non-aqueous systems. Particular attention has been applied to experiments on non-aqueous systems that are known to exhibit Hofmeister series in aqueous systems with the aim of determining if a consistent ion ordering in the strength of specific-ion effects is observed in other solvents. We find that specific-ion effects are ubiquitous in non-aqueous solvents, that both Hofmeister and lyotropic series are widely observed, although not necessarily for the same class of experiment. Moreover, we find that Hofmeister and lyotropic series are observed in non-aqueous solvents even for experiments in which these series are not observed for water. Additionally, series reversal is seen for a given experiment when the solvent is changed. All this poses significant challenges for our understanding of specific-ion effects in aqueous and non-aqueous systems and also provides guideposts for future investigations.     

Cadmium colloids from non-aqueous solvents

Cadmium colloids have been prepared by Chemical Liquid Deposition (CLD). The metal is evaporated to yield atoms which are solvated at liquid nitrogen temperature, and upon warming, stable liquid colloids are formed with particle size ranging between 25–100 Å. Zeta potentials were calculated according to the conversion of Hunter and the Hückel equation, for ethanol and dimethyl sulphoxide. UV/VIS measurement of most of the black colloids showed absorption band around 280 nm. For comparison, we prepared CdS colloid with size 400–625 Å. The colloids are stable to oxidation in air and/or oxygen bubbling. The synthesis of colloids and films from Cd with acetone, 2-butanone, ethanol, 2-propanol, 2-methoxyethanol, DMF and DMSO is reported. Transmission Electron Microscopy (TEM) allows us to determine particle size.     

Voltammetric studies of silane-modified SnO2 surfaces in selected aqueous and non-aqueous media

Voltammetric studies in selected aqueous and non-aqueous media were conducted for a series of silane-modified SnO₂ electrodes which had been further modified with a variety of metal phthalocyanines and metal cations. It is shown that tetrasulfonated, transitionmetal phthalocyanines can be both adsorbed and covalently attached to silane-modified surfaces where the silane has a coordinating ligand functionality such as a primary or secondary amine. It is further shown that the presence of the silane on the SnO₂ surface causes the appearance of a reversible voltammetric process following exposure of the surface to solution cation species. This reversible voltammetric wave is hypothesized to be due to the reduction of a surface bound Sn(IV) species to Sn(II) in a strongly hydroxylated environment.     

A computational approach to the spectrophotometric determination of stability constants-II Application to metalloporphyrin-axial ligand interactions in non-aqueous solvents

The ability of the computer program SQUAD to deduce a plausible equilibrium model, associated stability constants and spectra of individual species is described. The original version of SQUAD has been extensively modified and these changes are detailed. In particular a "user-friendly" method of data input has been implemented that simplifies familiarization with the program. Brevity of program code has been sacrificed in favour of the new data input and error-checking features of SQUAD, with beneficial results. The application of SQUAD to five non-aqueous metalloporphyrin-axial ligand interactions exemplifies the program's ability to handle widely different types of equilibrium systems.     

Foaming and antifoaming in non-aqueous liquids

Investigation into the physics of foaming has traditionally been focused on aqueous systems. Non-aqueous foams, by contrast, are not well understood, but have been the subject of a recent surge in interest motivated by the need to manage foaming across industrial applications. In this review, we provide a comprehensive discussion of the current state-of-the-art methods for characterizing non-aqueous foams, with a critical evaluation of the advantages and limitations of each. Subsequently, we present a concise overview of the current understanding of the mechanisms and methods used for stabilizing and destabilizing non-aqueous foams. We conclude the review by discussing open questions to guide future investigations.