High- and low-molecular-weight lignosulfonates and Kraft lignins as oil/water-emulsion stabilizers studied by means of electrical conductivity

Electrical conductivity measurements were used to study the creaming rates in oil/water emulsions stabilized with five lignosulfonates and one Kraft lignin. The creaming process resulted in a narrow dispersion band separating the water-rich and the oil-rich phases. An electrode was designed to follow this zone in the emulsion as a function of time. This makes it possible to calculate the amount of water separated from the emulsion directly from the creaming profiles. The stability concerning creaming was also evaluated with data obtained from visual inspection. Equivalent creaming profiles indicate that the electrode design used is suitable for stability measurements in the systems examined. Droplet interaction in diluted emulsions was studied with video-enhanced microscopy. Received: 10 September 1998 Accepted in revised form: 18 December 1998     

Emulsification properties of chitosan

 The chitosans use as an emulsifier in food emulsions was explored. The properties of chitosan (air/solution surface activity, electrical conductivity, HLB) were studied. The obtained emulsions were stable multiple w/o/w emulsions, whose characteristics were explained on the basis of the emulsifier structure and solution properties. The reaction with an anionic surfactant, sodium dodecylsulfate, was also studied, giving a water-insoluble complex at a given surfactant/chitosan ratio. Received: 24 March 1998 Accepted: 13 July 1998     

Highly hydrophobically modified polyelectrolytes stabilizing macroemulsions: relationship between copolymer structure and emulsion type

The types of emulsions, oil (n-dodecane) in water (O/W) or water in oil (W/O), stabilized with highly hydrophobically grafted linear poly(sodium acrylate)s, were investigated as a function of polymer chemical architecture. Consequently, a large number of macroemulsifiers, covering a wide range of hydrophobicity, were synthesized by changing the degree of grafting (τ), length (n) and type (single- versus twin-tailed) of the hydrophobic moiety. Monovalent salt (NaNO₃) concentration was used as a probe to adjust and hence to estimate the hydrophile-lipophile balance (HLB) of each copolymer. τ, n, type of graft and electrolyte concentration were identified as field parameters to control emulsion type. In general, decreasing either τ or n was found to favor the formation of direct emulsions. Inverse dispersions were preferentially formed with twin-tailed rather than single-tailed copolymers. Moreover, the types of emulsions stabilized with well-balanced polyelectrolytes can be flipped from O/W to W/O with increasing salt concentration. Finally, following the Davies concept, a HLB scale for polymers was created from a comparison with surfactants of nearly identical chemical structure. Received: 15 June 1998 Accepted: 12 August 1998     

Analytical control of organic additives in electrolytic baths by UV spectroscopy in combination with multivariate analysis

A method for the simultaneous determination of organic additives in Zn(II) and Ni(II) electrolytic baths is proposed. Absorbance and first-derivative spectra were subjected to direct and inverse multiple linear regression (CLS and ILS, respectively) in order to choose the optimum alternative. The use of a factor design to prepare the samples enables the identification of interactions between analytes and their correction by ILS. The results provided by first-derivative spectra were slightly better than those obtained with absorbance spectra (prediction errors were always less than 2% with the former). The ILS procedure was applied to three industrial baths used to a different extent, with highly satisfactory results. Received: 15 June 1998 / Revised: 7 September 1998 / Accepted: 15 September 1998     

Improved formulation of W/O/W multiple emulsion for insulin encapsulation. Influence of the chemical structure of insulin

W/O/W multiple emulsions are systems of potential interest in the oral administration of insulin. Although it has been shown that a single oral administration of insulin-loaded W/O/W multiple emulsion to diabetic rats led to the significant decrease of blood glucose levels (Silva Cunha et al., 1998, Int J Pharm 169:33), repeated administrations displayed unpleasant side effects such as diarrhoea and steatosis. These unwanted effects were attributed to the high oil concentration used for their preparation. In the present study, attention was focused on the reduction of oil concentration in the formulation of these systems and on the encapsulation of two different insulins. The physical properties and stability of the multiple emulsions over long periods of time were assessed by conductivity measurements, and granulometric and microscopic analyses. The encapsulation in the inner aqueous phase of two insulins, Umulin and Humalog, differing only by the transposition of one amino acid, had non-negligible effects on the formation and stability of W/O/W multiple emulsions. Both insulins were shown to improve the formation of the multiple emulsions. Circular dichroism studies and surface tension measurements evidenced the contribution of insulin conformation and surface properties in multiple emulsion formation and stability.     

Stabilization of emulsions by heterocoagulation of clay minerals and layered double hydroxides

 Paraffin/water emulsions were stabilized by colloidal particles without surface active agents. Mixtures of two types of particles with opposite signs of charge were used: a layered double hydroxide (the hydroxide layers carry positive charges) and the clay mineral montmorillonite (the silicate layers carry negative charges). The emulsions were very stable and did not separate a coherent oil phase. The stability of the emulsion (no oil coalescence after centrifugation) was independent of the mixing ratio of both the compounds when the total solid content was >0.5%. Solid contents up to 2.0% were optimal. In contrast to stability, flow behavior of the emulsion was dependent on the mass fraction χ of the hydroxide. The maxima of viscosity and yield value were observed at χ≈0.2–0.3; the emulsion showed pronounced antithixotropic behavior. Weak thixotropic properties, smaller viscosities and yield values were observed at χ≤0.2 and ≥0.5. In the absence of the clay mineral, the double hydroxide particles stabilize by forming envelopes around the oil droplets. Addition of bentonites creates a three-dimensional network of particles with high elasticity which impedes coalescence of the oil droplets. Received: 9 March 1998 Accepted: 6 April 1998     

Influence of the non-ionic surfactant PEG-660-12-hydroxy stearate on the surface properties of phospholipid monolayers and their effect on lipid emulsion stability

The effect of the interaction between phospholipid monolayers and PEG-660-12-hydroxy stearate as a non-ionic surfactant on lipid emulsion stability in dynamic and static conditions was studied. The presence of PEG-660-12-hydroxy stearate molecules with phospholipid monolayers (static state) leads to a remarkable increase in the surface pressure (from 5 to 30 mN/m in the initial molecular area), whereas in the dynamic state, when the two emulsifiers are separated and each dissolved in one phase of the two emulsion phases, a sudden decrease in the surface pressures is observed. This indicates that PEG-660-12-hydroxy stearate molecules are intercalated between the phospholipid monolayers forming a molecular mixed film. At the same time, a part of the phospholipid monolayers interacts with the surfactant monomers to form a soluble or partially soluble association complex. This interpretation was also supported by interfacial tension measurements, where the interfacial tension in the dynamic state was lower than that in the static one. This indicates that in static conditions the phospholipids partially interact with PEG-660-12-hydroxy stearate resulting in a non-active association complex. Subsequently there is insufficient utilization of the available surfactants during the emulsification process. In contrast, in dynamic conditions both emulsifiers are available at the free surface from the beginning. This behaviour was substantiated by investigating the stability of emulsions which were prepared either by the static condition or the dynamic one during the autoclaving process. Received: 25 May 1998 Accepted in revised form: 18 September 1998     

Soft X-ray spectromicroscopy on solid-stabilized emulsions

Oil–water emulsions stabilized by solids have been imaged with sub-100 nm spatial resolution and analyzed spectroscopically using a scanning transmission X-ray microscope. The emulsions are stabilized by particle heterocoagulate cages surrounding the oil droplets. These cages form due to the interaction of negatively charged clay mineral particles (sodium montmorillonite, Wyoming) and positively charged particles of calcium/aluminum layered double hydroxide (LDH). The emulsions were studied at atmospheric pressure, without any pretreatment using carbon K and calcium L X-ray absorption edges. Oil- and calcium-rich LDH were separately mapped, and the clay mineral dispersions were also imaged. Applying X-ray absorption-edge contrast, oil could be distinguished from water in the emulsion near the carbon K absorption edge (284 eV, 4.4 nm). Spectromicroscopy near the calcium L absorption edge (346 eV, 3.6 nm) allowed the structural details of heterocoagulate formation to be revealed. Received: 11 December 1998 Accepted in revised form: 10 January 1999     

A robotics-potentiometric method for the determination of mercaptan sulfur in fuels

A fully automated robotics method for the determination of mercaptan sulfur in several types of fuels is proposed. It is based on the standard method involving removal of sulfide with cadmium sulfate and subsequent determination. The robotics station develops both the preliminary operations and the determination. The method affords a precision, expressed as relative standard deviation, of 1.63%. The good agreement between the results obtained by the proposed and by conventional methods for the target analyte confirms its excellent performance and usefulness. Received: 1 July 1998 / Revised: 9 September 1998 / Accepted: 13 September 1998     

Study of the electrochemical behaviour of amphetamine and its derivatives in aqueous solution

The polarographic behaviour of amphetamine-type drugs in acid and alkaline solutions was investigated. Differential pulse polarography (DPP) with a dropping mercury electrode (DME) was used to monitor these drugs in aqueous solution. DPP and cyclic voltammetry (CV) were also utilised to study the electrode process of some 2-phenylethylamines derivatised with 4-N,N-dimethylaminobenzaldehyde (Ehrlich’s reagent) and 2,4-dinitrofluorobenzene, known as Sanger’s reagent, respectively. Received: 19 March 1998 / Revised: 17 September 1998 / Accepted: 21 September 1998     

Simultaneous determination of propanol and butanol by a fluorometric enzymatic method based on the intrinsic fluorescence of the enzyme

The application of the intrinsic fluorescence of alcohol dehydrogenase (ADH) for the simultaneous determination of propanol and butanol was investigated by using only one kinetic run. An absolute calibration method (based on a mathematical model derived from the enzymatic reaction) and a multivariate calibration method (partial least squares regression, PLSR) were tested for this purpose. Both methods were applied to synthetic samples of both alcohols with good results. Received: 17 September 1998 / Revised: 21 December 1998 / Accepted: 28 December 1998     

Yield stress and viscoelastic properties of high internal phase ratio emulsions

 The rheology of high internal phase ratio oil-in-water emulsions was investigated using a controlled-stress rheometer. The dispersed-phase (oil) concentration was varied from 71.24 to 89.61% by volume. Three different types of rheological experiments were conducted for each emulsion, namely: steady shear, oscillatory shear, and creep/recovery experiments. All the emulsions investigated in this study possess a yield stress. The yield-stress values obtained from different rheological experiments for the same emulsion show good agreement with each other. The yield-stress value increases exponentially with an increase in the dispersed-phase concentration. The yield-stress data of this study can be described quite well with the Princen and Kiss equation for high internal phase ratio emulsions provided that the thickness of the interdroplet films is taken into account. For any given emulsion, the storage modulus, measured in the linear viscoelastic region, is found to be constant, independent of the frequency, indicating a solid-like behaviour. The value of the storage modulus increases with an increase in the dispersed-phase concentration. The storage modulus data are interpreted in terms of the Princen and Kiss equation. Received: 23 October 1998 Accepted in revised form: 18 February 1999     

The Russian system for accreditation of analytical laboratories (centers)

 The history and the present state of the national system for accreditation of analytical laboratories in Russia are described. Received: 1 September 1998 / Accepted: 1 September 1998     

Emulsion liquid membrane separation of As(III) and As(V)

Emulsion liquid membranes (ELM) consisting of L113A (surfactant), liquid paraffin (stabilizer) and kerosene (solvent), with HCl solution acting as the external phase and KOH solution acting as the internal phase, were applied to the prior separation of arsenic(III) and arsenic(V) with subsequent spectrophotometric determination by AgDDTC. The effect of various parameters on the recovery of arsenic(III) were investigated. 8 mol/L HCl was required for 95% As(III) recovery. After reduction of As(V) to As(III) with sufficient KI, total arsenic could be determined. The RSD of As(III) and As(total) were both less than 3%. The procedure was applied to aqueous samples with a recovery of 93.5%–101%. Received: 22 March 1998 / Revised: 12 September 1998 / Accepted: 17 September 1998     

Emulsion liquid membrane separation of As(III) and As(V)

Emulsion liquid membranes (ELM) consisting of L113A (surfactant), liquid paraffin (stabilizer) and kerosene (solvent), with HCl solution acting as the external phase and KOH solution acting as the internal phase, were applied to the prior separation of arsenic(III) and arsenic(V) with subsequent spectrophotometric determination by AgDDTC. The effect of various parameters on the recovery of arsenic(III) were investigated. 8 mol/L HCl was required for 95% As(III) recovery. After reduction of As(V) to As(III) with sufficient KI, total arsenic could be determined. The RSD of As(III) and As(total) were both less than 3%. The procedure was applied to aqueous samples with a recovery of 93.5%–101%. Received: 22 March 1998 / Revised: 12 September 1998 / Accepted: 17 September 1998     

Optimised method of coal digestion for trace metal determination by atomic absorption spectroscopy

Understanding the transport of trace elements through a coal-fired power plant requires reliable analytical methods for these elements in all the ingoing and outgoing mass streams. Coal and different kinds of ashes comprise the most abundant mass streams in such a plant. As a continuation of our previous work, we have optimised a digestion method for the AAS determination of heavy metals in coal samples. It has become evident that complete dissolution of metals in coal samples and accurate results in subsequent analysis can be obtained by means of applying pressurised digestion under microwave heating. The combination of HNO₃ (conc.) and HF (conc.) in the volume ratio of 50 : 1 attacked the sample well enough, and good recoveries for all the metals studied were obtained. Surprisingly good results were obtained also when HNO₃ alone was used as the digestion acid. Received: 18 June 1998 / Revised: 23 September 1998 / Accepted: 24 September 1998     

Determination of Cu, Zn and Cd in water by FAAS after preconcentration by baker’s yeast (Saccharomyces cerevisiae) immobilized on sepiolite

By using the adsorbent Saccharomyces cerevisiae immobilized on sepiolite an adsorption-elution method was developed for the preconcentration of Cu, Zn, and Cd followed by flame atomic absorption spectrometry (FAAS). Recoveries were 98.3 ± 0.4% for Cu, 94.2 ± 0.3% for Zn, and 99.04 ± 0.04% for Cd at 95% confidence level obtained by the column method. The influence of sea water matrix elements on the separation of the trace elements was also assessed by using the column procedure. The breakthrough capacities were found to be 74 μmol/g for copper, 128 μmol/g for zinc and 97 μmol/g for cadmium. After optimization the proposed method was applied to the trace metal determination in sea and river water. Received: 8 June 1998 / Revised: 8 September 1998 / Accepted: 16 September 1998     

Direct subduction of Q-conjugacy representations to give characteristic monomials for combinatorial enumeration

Characteristic monomials for a finite group are obtained by direct subductions of Q-conjugate representations. They are shown to give a generating function that is capable of solving enumeration problems. Received: 1 May 1998 / Accepted: 16 July 1998 / Published online: 18 September 1998     

Bioavailability of silicon from food and food supplements

The bioavailability of silicon from three different silicon sources was studied. A diet rich in silicon, a tablet containing a dry extract of horsetail and a solution of silicon in a choline-glycerol matrix were compared. Blood and urine of one healthy test person were sampled to monitor the silicon uptake. The silicon content of blood and serum samples was determined by graphite furnace atomic absorption spectrometry. Strongly diverging results were obtained for the three different silicon sources. Neither an increase in urinary silicon excretion nor in serum silicon content was observed when feeding the silicon rich diet. Urinary silicon excretion did significantly (P < 0.05) rise during supplementation with tablets containing dry extract of horsetail. Intake of a solution of silicon in a choline-glycerol matrix resulted in a significantly (P < 0.05) increased urinary silicon excretion and serum silicon content. From these results it can be concluded that speciation (chemical form, matrix) strongly influences the bioavailability of silicon. Received: 3 August 1998 / Revised: 25 September 1998 / Accepted: 30 September 1998     

Effect of alkaline materials on interfacial rheological properties of oil-water systems

Interfacial rheological properties of a model crude oil-water system were studied in the presence of sodium hydroxide. The interfacial viscosity, the non-Newtonian flow behavior and the activation energy of viscous flow were determined as a function of shear rate, alkali concentration and aging time. The fundamental conclusion of the experimental results is that the interfacial viscosity drastically decreases in the presence of alkaline materials and the change under favorable conditions may exceed 3 or 4 orders of magnitude. Simultaneously, the sodium hydroxide effectively suppresses the non-Newtonian flow behavior of the interfacial layer. The experimental observations are explained by simultaneous chemical processes taking place in the boundary layer. The present data may help to elucidate the formation, stability and breaking of alkali-containing oil-water emulsions and they provide additional information for better understanding of the displacement mechanism and for the formulation of alkaline flooding as a potential chemically enhanced oil-recovery method. Received: 6 April 1998 Accepted: 18 August 1998