Low Conductivity Solutions Research Articles

Biological degradation of 1,2-dichloroethane under groundwater conditions

To gain a better understanding of the applicability of bacteria with special metabolic properties to purify polluted groundwaters, we have investigated the mineralization of low concentrations of 1,2-dichloroethane (DCA) in two different bioreactors which were inoculated with a mixture of two pure cultures capable of mineralizing DCA. Degradation experiments were continuously run at neutral pH at temperatures of between 10 and 30°C and in solutions of low conductivity (c. 1000 μS cm −1) thus simulating groundwater pumped from a polluted site. DCA concentrations in the feed ranged from 1 to 25 mg l −1. Oxygen was monitored in the reaction effluent and was added to the feed if required as a solution of H 2O 2. The fixed bed bioreactor with sintered glass beads as carrier was run in a flow-through mode with a hydraulic retention time of 2–3 h. DCA mineralization, determined by the disappearance of DCA, the consumption of oxygen, the decrease in pH and the formation of chloride ions, started 3 weeks after inoculation. After this time, at least 80% of DCA was mineralized with DCA feed concentrations of 20–25 mg l −1. DCA elimination efficiency increased up to 90% with increasing running time. With a feed concentration of 10 mg l −1 DCA. DCA effluent concentration decreased further to below 300 μg l −1. This degradation efficiency was independent of the different temperatures applied. Using granular activated carbon as carrier-material for the micro-organisms and running the reactor with a recycle at the same hydraulic residence time, mineralization started 5 weeks after inoculation. DCA effluent concentration was between 1 and 2 mg l −1 with feed concentrations of up to 20 mg l −1 DCA. The ability to mineralize DCA was kept without feeding the micro-organisms for 3 weeks.

Ti/IrO2 as anode and Zr as cathode in multicompartment electrolyzers with Immobiline membranes.

Multicompartment electrolyzers with isoelectric Immobiline membranes are used for large-scale preparative protein purification. A series of isoelectric membranes, of defined pI values, is utilized for keeping any desired species isoelectric within each compartment of the electrolyzer. It is preferable to have electrode disks of the same surface area as the membranes for a proper performance of the instrument because electrolyte solutions of low conductivity are used. The use of Pt disks would be quite expensive; we therefore propose using Zr as a cathode and Ti/IrO2 as an anode in the electrodic compartments. This pairing of electrodes seems to give the same performance as Pt wires. Also, conventional isoelectric focusing, as well as isoelectric focusing in immobilized pH gradients, both requiring a good contact area between gel and electrodes, would benefit by using flat laminae of these metals as electrodes.

Field amplified sample injection in high-performance capillary electrophoresis

A simple on-column concentration technique in high-performance capillary electrophoresis (HPCE) is reported. In conventional electro-injection in HPCE, samples are prepared in a buffer solution which has the same concentration as that inside the capillary column. The amount of ions injected into the column under this condition is limited. By preparing samples in a low-conductivity solution, e.g., water, and injecting the sample solution electroosmotically into the column, one can achieve a field enhancement at the injection point. The amount of ions injected will then be proportional to this enhancement factor. However, if one samples by switching the column directly from the high-conductivity buffer reservoir to the low-conductivity sample solution, the buffer boundary at the end of the column is disturbed and the electric field at the injection point might not be amplified properly. By injecting a short plug of water before sample introduction, one can provide a high electric field strength from the beginning of the injection. Several hundred-fold enhancements in the amount of injection were confirmed experimentally.

Amperometric monitoring of sulphur dioxide in liquid and air samples of low conductivity by electrodes supported on ion-exchange membranes

An amperometric sensor is described for the determination of sulphur dioxide in both gaseous atmospheres and solutions of low conductivity. It consists of a porous Pt electrode (facing the sample) supported on one face of an ion-exchange membrane (Nafion 417) which serves as a solid polymer electrolyte. The other side of the membrane faces an internal electrolyte solution (1 mol dm–3 aqueous perchloric acid) containing the counter and reference electrodes. This sensor is inserted into a flow cell in which gaseous or electrolyte-free aqueous samples are fed by a peristaltic pump placed in a closed-loop path and SO2 is oxidized at an applied potential of 0.65 V versus Ag–AgCl. The device is found to be characterized by a high current sensitivity and a short response time, 24 A cm–2 mol–1 dm3 and 1 s respectively for gaseous samples; (0.4 A cm–2 mol–1 dm–3 and 4 s, respectively, for water solutions), and by good stability and low background noise. The dynamic range extends up to 2 × 10–4 mol dm–3(gaseous samples) and 1 × 10–3 mol dm–3(water samples) with good linearity, and detection limits of 8 × 10–9 mol dm–3(gaseous samples) and 4 × 10–7 mol dm–3(water samples) are predicted for a signal-to-noise ratio of 3. The advantages offered by this type of sensor over conventional gas-permeation membrane electrodes are discussed.

Explanation of high-frequency phase shift in ac impedance measurements for copper in low-conductivity media

The high-frequency phase shift is caused by the salt bridge, not by the sce itself. The resistance and the capacitance is believed to occur in the contact region between the low-conductivity solution and the tip of Luggin capillary.

The Error in Polarization Resistance and Capacitance Measurements Resulting from Nonuniform Ohmic Potential Drop to Flush-Mounted Probes

Abstract The possibility of encountering a systematic error in polarization resistance measurements resulting from the nonuniform ohmic potential drop to flush-mounted electrodes is investigated. The error is introduced even though the ohmic potential drop is considered by use of the interrupter technique or by measurement of AC impedance at high frequencies. The error is significant when the ohmic potential drop is large, for example, in the presence of high corrosion rates and low-conductivity solutions. Correction factors are calculated for a disk electrode immersed in a bulk electrolyte or covered by a thin film of conducting solution.

Voltammetric measurements with microelectrodes in low-conductivity systems

It is shown that voltammetric measurements can be made in solutions of low conductivity and low dielectric permitivity by using appropriate microelectrodes, the oxidation of ferrocene in toluene+ acetonitrile being used to explore the behaviour. At high concentrations of acetonitrile, measurements can be made at low or zero concentrations of supporting electrolyte; with decreasing concentration of acetonitrile, increasing concentrations of supporting electrolyte are required to determine the voltammetric curves. Simple corrections for ohmic potential drops in the solution can be applied but the procedures fail for solutions of very low dielectric permittivity, probably because of ion-pair formation near the electrode surface.

Corrosion in solar heating systems. II. Corrosion behaviour of AA 6351 in water/glycol solutions

AbstractA research was carried out in order to investigate the corrosion behaviour of the metals most commonly used as construction materials for solar absorber plates.With this view, an attempt was made to test the corrosion resistance of the aluminium alloy AA 6351 (nominal composition: 1% Si, 0.6% Mg, 0.3% Mn, the balance Al) towards common uninhibited heat transfer fluids, such as ethylene and propylene glycol/water mixtures.Long time gravimetric tests consisted in up to 60 day exposures of the aluminium specimens to pure, chloride‐polluted, or degraded glycol/water solutions, at the temperature of 80°C. The degradation into acidic products, experienced by heat transfer liquids in service, was simulated by keeping the ethylene and propylene glycol/water solutions at their boiling temperature for 30 days, in contact with copper.In glycol/water solutions the presence of chlorides at low concentration (200 ppm) caused the aluminium corrosion rates to increase by more than one order of magnitude, while in degraded solutions, containing 143 or 86 ppm cupric ions, corrosion rates higher than two order of magnitude with respect to pure solutions were obtained.During the gravimetric tests, pitting corrosion was observed in some cases and its extent was rated by evaluating the deepest and the average metal penetration, the pit density and the average pit size.The influence of heat transfer on the alloy AA 6351 corrosion and on the couple copper/AA 6351 efficiency was evaluated by gravimetric and electrochemical tests. Heat transfer through aluminium was found to significantly increase the aluminium alloy pitting potential. On the contrary, it stimulated the aluminium galvanic corrosion, when applied on either aluminium or copper.Under galvanic coupling conditions, the aluminium corrosion rates calculated from the average galvanic currents were a very little contribution to the gravimetric corrosion rates. This demonstrates that in low conductive solutions the risk of matching such dissimilar metals as copper and aluminium does not reside in the galvanic contact itself, but mainly in the mere presence of the noblest metal in the same solution where aluminium is immersed.

Fretting in aqueous media, particularly of roping steels in seawater

A model is described to account for the wear rates, coefficients of friction and surface features observed when fretting a 0.64% C high tensile roping steel in seawater. The work includes a comparison of the fretting behaviour, both in air and in selected aqueous environments, with that of an austenitic stainless steel. When fretting in air, mechanical and oxidational components are suggested, although in aqueous solutions an additional electrochemical corrosion component becomes important. Although a liquid can help to reduce friction by acting as a lubricant, the effects of which are most noticeable in the early stages of fretting, under most circumstances the liquid will give rise to a corrosion process which accounts for high wear rates and ultimately to increasing coefficients of friction through the accumulation of trapped corrosion debris. Only in solutions of low ionic conductivity and/or very low dissolved oxygen concentration can the corrosion rate be reduced, but only by the application of a suitable level of cathodic protection can it be eliminated altogether to achieve desirable friction and wear behaviour. A number of experiments were carried out in artificial seawater to give some indication of the fretting corrosion behaviour of roping steels used in offshore environments.

The generation of electric currents by the laminar flow of dielectric liquids

The electric current generated by the laminar flow of an insulating liquid through a cylindrical pipe has been calculated using a model that incorporates nonequilibrium boundary conditions at the wall. Analytical solutions to the model equations are derived in the limits of high and low electrical conductivity and numerical solutions are given at intermediate conductivities. The solutions depend on four parameters that are dimensionless representations of the electrical conductivity, the rate of adsorption of positive ions, the rate of adsorption of negative ions and the ratio of the diffusivities of positive and negative ions. The results are presented as graphs of current versus the electrical conductivity parameter for various values of the other three parameters. Physical reasons for the shapes of the current/conductivity curves are discussed. According to the model, the currents are generated by differences in the ionic diffusivities and/or by differences in the ionic adsorption rates at the wall.

Nutrition and growth of birch and grey alder seedlings in low conductivity solutions and at varied relative rates of nutrient addition

Birch (Betula verrucosa Ehrh.) and grey alder (Alnus incana Moench) seedlings were grown with varied relative addition rates of all nutrients, up to optimum for vegetative growth. The root medium was basically distilled water to which the nutrients, contained in stock solutions in fixed proportions, were added every second hour and in exponentially increased amounts for consumption during the subsequent period. The nutrient weight proportions previously found to be required in birch (100 N:65 K:13 P) were used in all treatments. However, the nutrient proportions required in grey alder were found to be somewhat different (100 N:50 K:18 P). The use of the required proportions in the additions was important for maintenance of maximum growth, efficient nutrient utilization, and low concentrations in the root medium. Luxury consumption and inefficiency occurred at high concentrations. The results show that the nutrient requirements are sufficiently defined, for different relative growth rates, by the nutrient proportions and the relative addition rate.No clear relationships were found between conductivity or concentration in the root medium and the addition rate, net uptake rate, nutrient status, or relative growth rate. The results are in good agreement with data from low concentration and depletion experiments reported in the literature, showing that non‐limited uptake rates occur down to very low concentrations. Thus, there is strong evidence that concentration has been incorrectly used when applied as the treatment variable for plant nutrition in plant science and cultivation practice. The dominant factors in sub‐optimum and optimum nutrition are the amounts of nutrients available per unit of time, the growth rate, and the nutrient proportions. At low concentration levels, physical factors such as stirring and flow rate of nutrient solution and boundary layer effects are decisive for the rates with which the nutrients become available to the roots. Therefore, at low levels, concentration alone cannot be used as the factor determining nutrient uptake rate. At high levels, concentration is effective as a supra‐optimum factor and increased internal percentage contents cause decreased uptake efficiency, thus counter‐acting the concentration effect.Nitrogen effects dominated the stress indications when the internal nitrogen percentage content decreased from optimum to the level of the treatments in the beginning of the experiments. Leaf deficiency symptoms disappeared and the root/shoot ratio change ceased when nitrogen status stabilized. Strong linear regressions were found between any two of the variables: relative addition rate of nutrients, relative growth rate, and nutrient status.

Growth and nutrition of three Salix clones in low conductivity solutions

The ability of Salix aquatica Smith, S. fragilis L. and S. vlminalis L. to grow in low conductivity solutions was investigated. The effects of four different relative nutrient addition rates on the N, K, P, Ca, and Mg contents of the plants, on concentrations in the media, and on dry matter distribution between roots, stems, and leaves, were measured. No significant and persistent increase of concentration of any element resulting from the daily nutrient additions was measured in the media. Practically all nutrients were consumed by the plants at the same rate and in about the same proportions at which they were supplied. Linear regressions were found between any two of the three factors: relative rate of nutrient supply, nitrogen status, and relative growth rate. High nutrient addition rates favoured leaf development while low nutrient addition rates stimulated root growth. It is concluded that the decisive factor governing the mineral uptake rate in Salix is the rate of nutrient supply and that these clones are well suited for short rotation energy forestry in so far as their ability to absorb the mineral elements efficiently is concerned.

Muscle fiber capacity in low conductivity solution.

A method is described for computing the effective capacity of muscle fibers, C = Q/V where Q is the charge stored, and V is the membrane potential, using a standard two-microelectrode, constant current injection technique. The method is used to compare physical (or effective) capacity of frog muscle fibers bathed in a low conductivity, 2.5 mMK+ solution, with circuittheory derived quantities in the same cells and in control fibers. No differences can be discerned and it is concluded that low conductivity of physiological solutions, per se, does not significantly reduce the length constant of frog muscle transverse tubules.

An analysis of light-induced admittance changes in rod outer segments.

1. Measurements were made of the time course and amplitude of the change in real part of admittance, DeltaG, of a suspension of frog rod outer segments, following a flash of light bleaching about 1% of the rhodopsin content of the rods. The measurements, based on the use of a specially designed marginal oscillator, covered the frequency range between 500 Hz and 17 MHz.2. The components of response, previously described for rods prepared by a method involving exposure to strongly hypertonic sucrose solutions, are present in similar form when rods are isolated and maintained in isotonic solutions made up with equi-osmotic concentrations of NaCl and sucrose or with Na(2)SO(4).3. Component I, identified as a slowly developing positive DeltaG apparent at very low frequencies, is frequency-independent up to the characteristic frequency of admittance for the suspension, f(Y) (about 2 MHz for rods suspended in a solution having the conductivity of Ringer solution), but decreases at still higher frequencies.4. Component II, identified as a rapidly developing positive DeltaG which appears only above a critical frequency about 2.5 decades below f(Y), increases approximately logarithmically with frequency to reach a limiting amplitude in the region of f(Y).5. The amplitude of component II, DeltaG(II), measured in the region of f(Y), varies linearly with the conductivity of the suspending medium, G(o), under conditions in which the conductivity of the rod interior is also a linear function of the external conductivity. The relation for a flash bleaching 1% of the rhodopsin content of the dark-adapted rod is [Formula: see text]6. Measurements made on rods suspended in a low-conductivity solution, which has the effect of reducing the conductivity of the rod interior to about one ninth its value for rods suspended in Ringer solution, reveal a decline in component II for frequencies above 8 MHz.7. To explain the frequency dependence of component II and its dependence on conductivity, it is proposed that component II arises from a light-induced increase in conductance of the disk membranes which obstruct the longitudinal flow of current through the rod interior except at very high frequencies.8. The disk-membrane conductance increase for rods suspended in a solution having the conductivity of Ringer solution is calculated to be 4.3 x 10(-11) mho/rhodpsin molecule bleached, a value which is similar to what has been found for ionic channels operated by membrane potential change in the nerve membrane and by synaptic transmitter in the postjunctional membrane.9. No component of response has been observed which could be reliably attributed to a surface membrane conductance decrease of the type observed in receptor cells in the retina.

Measurement of differential capacitance in solutions of low conductivity

An experimental set-up for measuring the differential capacitance at the dme for cell resistances up to several M is described. The system performance is analysed and experimental differential capacitance vs potential curves at the interface between the dme and 10−3, 10−4, 10−5 M NaF are presented. The method involves the measurement of the charging current when a linear sweep is supplied to the cell, utilizing positive feedback for the compensation of the cell resistance. Positive feedback for compensation is found to be especially useful for equilibrium capacitance measurements since it accelerates the attainment of equilibrium. Instrumental errors and the relation between the accuracy of the capacitance measurement and the error in compensation are discussed. The experimental results for 10−3, 10−4, 10−5 M NaF are compared with values expected on the basis of Grahame's data for higher concentrations. Agreement is found between experimental and calculated capacitances in the region of zero charge. In the negative polarization region experimental capacitances are lower than calculated capacitances and decrease progressively with decreasing concentrations.

A theoretical analysis of the capacitance of muscle fibers using a distributed model of the tubular system.

A model is developed to predict the changes in total capacitance (i.e. total charge stored divided by surface membrane potential) of the tubular system of muscle fibers. The tubular system is represented as a punctated disc and the area of membrane across which current flows is represented as a punctated annulus, the capacitance of the muscle fiber being proportional to this area. The area can be determined from a distributed model of the tubular system, in which the only resistance to radial current flow is presumed to be in the lumen of the tubules. Calculations are made of the variation of capacitance expected as the conductivity of the bathing solution is varied. These calculations include the effects of fixed charge in the tubular lumen and the effects of changes in the shape and volume of the tubular system in solutions of low conductivity. The calculated results fail to fit comparable experimental data, although they do qualitatively account for the known variation of the radial spread of contraction with conductivity of the bathing medium. It is pointed out that the existence of a significant "access resistance" at the mouth of the tubules might explain the discrepancy between theory and experiment.

Current distribution on a rotating disc electrode

In solutions of low conductivity, the current at a rotating disc electrode may not be uniform. A simplified but more approximate version of Newman's theory 1 is presented, together with a diagnostic diagram for whether the effect will be important or not in any particular experiment.

The dipolar origin of protein relaxation.

1. A set of parameters is proposed to check the interpretation of the dielectric behaviour of protein solutions as a rigid-dipole relaxation of prolate ellipsoids of revolution in the frequency range between 20 kHz and 10 MHz. Besides the delta(b)-function of Scheraga, another analogous function (delta(a)) is presented to establish size and shape of globular proteins. A study of the influence of solvent viscosity on the dielectric dispersion also gives strong evidence in favour of rigid-dipole relaxation. 2. Measurements of the dielectric dispersion of monomer solutions of bovine serum albumin and transferrin are reported. Monomers of bovine serum albumin were obtained by fractionation on Sephadex G-150. Low-conductivity solutions of both proteins are obtained by passage through an ion-exchange resin. 3. Computer analysis of the experimental dispersion curves by use of a two-term Debye dispersion gives valuable information about transferrin and leads to an axial ratio 4.5 for a prolate ellipsoid of revolution. The dielectric increment of bovine serum albumin is very low and no conclusive results have yet been obtained.

Differential capacitance measurements with the dropping mercury electrode in solutions of low conductivity

Differential capacitance measurements with the dropping mercury electrode in solutions of low conductivity

Differential capacitance measurements with the dropping mercury electrode in solutions of low conductivity

Differential capacitance measurements with the dropping mercury electrode in solutions of low conductivity