Concentrations Of Other Solutes Research Articles

Phase Equilibria for the Glycine–Methanol–NH4Cl–H2O System

An investigation of the phase equilibria of the glycine–methanol–NH4Cl–H2O system was carried out with the objective of optimizing the monochloroacetic acid (MCA) process for the production of glycine. Phase equilibrium of the glycine–NH4Cl–H2O system at temperatures over the range of 283.2–353.2 K was determined for concentrations ranging up to the multiple saturation points. The solubilities of both glycine and NH4Cl were found to increase with increasing temperature, as well as with increasing concentration of other solutes. The Bromley–Zemaitis model for ions and the Pitzer formulation for glycine neutral species implemented in the OLI platform were used in the regression of the experimental solubilities. The average absolute deviations between the regressed solubility values and the experimental data were found to be 1.4% for glycine and 0.93% for NH4Cl. Three binary interaction parameters of the Pitzer formulation were newly obtained and coupled with the Bromley–Zemaitis parameters documented in OLI’s databank to predict the multiple saturation points of the system. Additionally, the solubility of glycine in methanol–H2O mixtures was also measured from 283.2 to 323.2 K, and a sharp decline was observed as a function of the content of methanol. Such thermodynamic information is definitely useful for improving the existing industrial process, as well as providing fundamentals for the development of new glycine production processes.

Changes in the chemistry of shallow groundwater related to the 2008 injection of CO2 at the ZERT field site, Bozeman, Montana

Approximately 300 kg/day of food-grade CO2 was injected through a perforated pipe placed horizontally 2–2.3 m deep during July 9–August 7, 2008 at the MSU-ZERT field test to evaluate atmospheric and near-surface monitoring and detection techniques applicable to the subsurface storage and potential leakage of CO2. As part of this multidisciplinary research project, 80 samples of water were collected from 10 shallow monitoring wells (1.5 or 3.0 m deep) installed 1–6 m from the injection pipe, at the southwestern end of the slotted section (zone VI), and from two distant monitoring wells. The samples were collected before, during, and following CO2 injection. The main objective of study was to investigate changes in the concentrations of major, minor, and trace inorganic and organic compounds during and following CO2 injection. The ultimate goals were (1) to better understand the potential of groundwater quality impacts related to CO2 leakage from deep storage operations, (2) to develop geochemical tools that could provide early detection of CO2 intrusion into underground sources of drinking water (USDW), and (3) to test the predictive capabilities of geochemical codes against field data. Field determinations showed rapid and systematic changes in pH (7.0–5.6), alkalinity (400–1,330 mg/l as HCO3), and electrical conductance (600–1,800 μS/cm) following CO2 injection in samples collected from the 1.5 m-deep wells. Laboratory results show major increases in the concentrations of Ca (90–240 mg/l), Mg (25–70 mg/l), Fe (5–1,200 ppb), and Mn (5–1,400 ppb) following CO2 injection. These chemical changes could provide early detection of CO2 leakage into shallow groundwater from deep storage operations. Dissolution of observed carbonate minerals and desorption-ion exchange resulting from lowered pH values following CO2 injection are the likely geochemical processes responsible for the observed increases in the concentrations of solutes; concentrations generally decreased temporarily following four significant precipitation events. The DOC values obtained are 5 ± 2 mg/l, and the variations do not correlate with CO2 injection. CO2 injection, however, is responsible for detection of BTEX (e.g. benzene, 0–0.8 ppb), mobilization of metals, the lowered pH values, and increases in the concentrations of other solutes in groundwater. The trace metal and BTEX concentrations are all significantly below the maximum contaminant levels (MCLs). Sequential leaching of core samples is being carried out to investigate the source of metals and other solutes.

Trends in pollutant concentrations in relation to time of recharge and reactive transport at the groundwater body scale

Summary To quantify the threat of pollutants to present and future groundwater quality requires detecting trends in groundwater quality. We related the measured concentrations of pollutants from selected monitoring locations in the Sand Meuse groundwater body to the time of recharge determined by 3 H/ 3 He as a means to aggregate the measurements and detect trends that are significant for the entire groundwater body. The aim of this study was to (1) define under what conditions the concentrations of reactive solutes may be related to travel times; (2) identify solute specific trends; (3) assess which geochemical processes are responsible for these trends using a geochemical model (PHREEQC); and (4) distinguish between different types of trends. The observed trends in the concentrations of Cl are solely the result of historical changes in chloride concentrations in recharging groundwater. Cation exchange influences the trends in the concentrations of K and Ca, and heavy metals, and to a lesser extent also Na and Mg. Trends in the concentrations of NO 3 and SO 4 are the combined result of changing recharge concentrations and the process of pyrite oxidation. Fe, As, Ni and Zn are released during pyrite oxidation and these trends are indirectly the result of changing land use practices. We distinguish three types of trends in the concentrations of solutes related to time of recharge. These are the result of: (1) the anthropogenic trends in historical concentrations in recharging groundwater unaltered during conservative transport through the groundwater body, (2) anthropogenic trends in recharge concentrations altered by reactions during transport and (3) geochemical reactions in the subsurface that are triggered by anthropogenic changes in the recharge concentrations of other solutes.

Arsenic attenuation by oxidized aquifer sediments in Bangladesh

Recognition of arsenic (As) contamination of shallow fluvio-deltaic aquifers in the Bengal Basin has resulted in increasing exploitation of groundwater from deeper aquifers that generally contain low concentrations of dissolved As. Pumping-induced infiltration of high-As groundwater could eventually cause As concentrations in these aquifers to increase. This study investigates the adsorption capacity for As of sediment from a low-As aquifer near Dhaka, Bangladesh. A shallow, chemically-reducing aquifer at this site extends to a depth of 50 m and has maximum As concentrations in groundwater of 900 microg/L. At depths greater than 50 m, geochemical conditions are more oxidizing and groundwater has <5 microg/L As. There is no thick layer of clay at this site to inhibit vertical transport of groundwater. Arsenite [As(III)] is the dominant oxidation state in contaminated groundwater; however, data from laboratory batch experiments show that As(III) is oxidized to arsenate [As(V)] by manganese (Mn) minerals that are present in the oxidized sediment. Thus, the long-term viability of the deeper aquifers as a source of water supply is likely to depend on As(V) adsorption. The adsorption capacity of these sediments is a function of the oxidation state of As and the concentration of other solutes that compete for adsorption sites. Arsenite that was not oxidized did adsorb, but to a much lesser extent than As(V). Phosphate (P) caused a substantial decrease in As(V) adsorption. Increasing pH and concentrations of silica (Si) had lesser effects on As(V) adsorption. The effect of bicarbonate (HCO(3)) on As(V) adsorption was negligible. Equilibrium constants for adsorption of As(V), As(III), P, Si, HCO(3), and H were determined from the experimental data and a quantitative model developed. Oxidation of As(III) was modeled with a first-order rate constant. This model was used to successfully simulate As(V) adsorption in the presence of multiple competing solutes. Results from these experiments show that oxidized sediments have a substantial but limited capacity for removal of As from groundwater.

Effect of clear-cutting and site preparation on the level and quality of groundwater in some headwater catchments in eastern Finland

The impact of forest management (clear-cutting and site preparation) on stream hydrology has been studied in five small catchments in eastern Finland from 1991 and on groundwater levels and quality from 1994. The period 1992–1996 was a calibration period and in the autumn of 1996, 10% and 30% of the area of two of these catchments were clear-cut according to the forest management plan. Regeneration was carried out by disc-plowing in the autumn of 1998 and planting with Scots pine ( Pinus sylvestris) and Norway spruce ( Picea abies) seedlings in the spring of 1999. The depth and quality of groundwater was monitored with four to nine groundwater wells installed in each catchment. There were 32 wells in all, 16 on upland mineral soils and 16 on peatlands (the perforated part of the pipe was totally put into the underlying mineral soil at eight sites). Sampling was made monthly during spring (March–May) and autumn (November–December) and bimonthly during summer (June–October). The samples were chemically analyzed for pH, electrical conductivity, and concentrations of total P and Fe (before filtration), and total N, NO 3 −-N, NH 4 +-N, total P, PO 4 3−-P, SO 4 2−-S, Ca 2+, Mg 2+, K +, Na +, Mn, Zn, Fe, Al 3+, Cl − (after filtration through 0.45 μm membrane filter). Data collected until the end of 2001 are reported. Groundwater was found in the down-slope wells in lower-lying areas, but not in those installed on the slopes with a thin (1–2 m) soil layer. Clear-cutting did not significantly affect groundwater levels in the wells. Nitrate N concentrations increased from 0.03 mg L −1 level after clear-cutting and again after site preparation in the wells on upland soils and peatlands receiving water from the managed parts of the catchment. In one well at the lower edge of the managed area NO 3 −-N concentrations reached 1–1.4 mg L −1 in 2001 (fifth year after clear-cutting, third after disc-plowing), but mean concentrations remained <0.3 mg L −1. Chloride concentrations also increased (50–100%) after treatments but the concentrations of other solutes showed no significant effect of treatment. It was concluded that changes in groundwater quality and quantity related to the clear-cutting were small and did not represent a danger to water quality or quantity.

A Thermodynamic Interpretation of the “Excluded-Volume Effect” in Coupled Diffusion

Strongly coupled diffusion has been reported for fluxes of solutes that differ significantly in molecular size. According to the excluded-volume model, a solute increases the effective concentrations of other solutes by reducing the volume of solution they can occupy. The flux of solute 2 produced by the gradient ∇c1 in the concentration of solute 1 is interpreted as the ordinary diffusion of solute 2 down its effective concentration gradient. Cross-diffusion coefficient D21 = D22c2V1,eff/(1 − c1V1,eff)2 is predicted, where V1,effis the effective molar volume of solute 1. This model does not account for countercurrent coupled diffusion (D21 < 0) and is found to be inconsistent with the Onsager reciprocal relation (ORR). A thermodynamic model of coupled transport is developed by approximating the flux of solute i as the product of its concentration, mobility, and chemical potential gradient driving force (−∇μi), which gives D21 = D22c2(V1 − V0)/[1 − c1(V1 − V0)], where Vi is the partial molar volume of component i and the solvent is component 0. For dilute solutions with V1 ≫ V0, the thermodynamic prediction D21 ≈ c2V1D22 and the excluded-volume prediction D21 ≈ c2V1,effD22 are qualitatively similar, but the thermodynamic model does not require the assumption of effective concentrations or effective volumes, provides a physical explanation for coupled diffusion, and is consistent with the ORR. Moreover, because ∂μ2/∂c1 is proportional to V1 − V0, the thermodynamic model suggests that a concentration gradient in solute 1 can drive co-current or counter-current flows of solute 2, depending on the relative volumes of solute 1 and solvent 0. These features are illustrated by comparing measured and predicted Dik coefficients for solutions of n-octane(1) + n-hexadecane(2) in n-dodecane(0) at nine different compositions at 25 °C.

Massive reduction of urea transporters in remnant kidney and brain of uremic rats

The facilitated urea transporters (UT), UT-A1, UT-A2, and UT-B1, are involved in intrarenal recycling of urea, an essential feature of the urinary concentrating mechanism, which is impaired in chronic renal failure (CRF). In this study, the expression of these UTs was examined in experimentally induced CRF. The abundance of mRNA was measured by Northern analysis and that of corresponding proteins by Western blotting in rats one and five weeks after 5/6 nephrectomy (Nx). At five weeks, urine output was enhanced threefold with a concomitant decrease in urine osmolality. The marked rise in plasma urea concentration and fall in urinary urea concentration resulted in a 30-fold decrease in the urine/plasma (U/P) urea concentration ratio, while the U/P osmoles ratio fell only fourfold. A dramatic decrease in mRNA abundance for the three UTs was observed, bringing their level at five weeks to 1/10th or less of control values. Immunoblotting showed complete disappearance of the 97 and 117 kD bands of UT-A1, and considerable reduction of UT-A2 and UT-B1 in the renal medulla. Similar, but less intense, changes were observed at one-week post-Nx. In addition to the kidney, UT-B1 is also normally expressed in brain and testis. In the brain, its mRNA expression remained normal one-week post-Nx, but decreased to about 30% of normal at five-weeks post-Nx, whereas no change was seen in testis. (1) The decline in urinary concentrating ability seen in CRF is largely due to a major reduction of UTs involved in the process of urea concentration in the urine, while factors enabling the concentration of other solutes are less intensely affected. (2) The marked reduction of brain UT expression in CRF may be responsible for brain edema of dialysis disequilibrium syndrome observed in some patients after fast dialysis.

A mini drivepoint sampler for measuring pore water solute concentrations in the hyporheic zone of sand‐bottom streams

A new method for collecting pore‐water samples in gravel streambeds is presented. We developed a mini drivepoint solution sampling (MINIPOINT) technique to collect pore‐water samples at 2.5‐cm vertical resolution. The sampler consisted of six small‐diameter stainless steel drivepoints arranged in a 10‐cm‐diameter circular array. In a simple procedure, the sampler was installed in the streambed to preset drivepoint depths of 2.5, 5.0, 7.5, 10.0, 12.5, and 15.0 cm. Sampler performance was evaluated in the Shingobee River, Minnesota, and Pinal Creek, Arizona, by measuring the vertical gradient of chloride concentration in pore water beneath the streambed that was established by the uninterrupted injection to the stream for 3 d. Pore‐water samples were withdrawn from all drivepoints simultaneously. In the first evaluation, the vertical chloride gradient was unchanged at withdrawal rates between 0.3 and 4.0 ml min− but was disturbed at higher rates. In the second evaluation, up to 70 ml of pore water was withdrawn from each drivepoint at a withdrawal rate of 2.5 ml min−1 without disturbing the vertical chloride gradient. Background concentrations of other solutes were also determined with MINIPOINT sampling. Steep vertical gradients were present for biologically reactive solutes such as DO, NH4+, NO3−, and dissolved organic C in the top 20 cm of the streambed. These detailed solute profiles in the hyporheic zone could not have been determined without a method for close interval vertical sampling that does not disturb natural logic mixing between stream water and groundwater.

High-performance ion chromatography applied to free-radical mechanisms in drug design the problem of ion analysis at high ionic strengths

Putative free-radical intermediates in drug action can be studied by radiolysis of model systems containing low concentrations of drug and much higher concentrations of other solutes to scavenge the primary water radicals and convert them into appropriate oxidants or reductants. The need to employ high ionic solute concentrations (typically >10 mmol dm −3) represents a challenge for the high-performance ion chromatographic detection of drug-derived ions (typically, <50 μmol dm −3). Constraints on the chromatographic method chosen are illustrated with examples of the application of high-performance ion chromatography (HPIC) to radiation chemistry studies in the oxidative decar☐ylation of the anti-tumour drugs flavone-8- and xanthenone-4-acetic acids and structurally related aromatic car☐ylic acids (CO 2 in the form of CO 3 2−), the oxidative denitrification of nitric oxide precursor molecules (NO in the form NO 2 −/NO 3 −) and the generation of SO 4 2− from novel thiol-based (perthiol) drugs.

Nucleation and Crystal Growth in a Vitrification Solution Tested for Organ Cryopreservation by Vitrification

Nucleation and crystal growth are investigated for vitrification solution VS41A (dimethyl sulfoxide, formamide, and 1,2-propanediol) in an aqueous carrier solution giving, when added to these three cryoprotectants, a concentration of other solutes in the whole solution the same as that in Euro-Collins, with a 55% (w/v) cryoprotectant concentration. This concentration is assumed to achieve physical properties under 1 atmosphere similar to those of solution VS4 used under 1000 atmospheres. The thermal range and the kinetics of nucleation and crystal growth are investigated by DSC through different thermal treatments. It is found that the nucleation thermal range is below -90°C and that of crystal growth is above -85°C for a relatively long experimental time. The nucleation density is also studied through direct observations by cryomicroscopy and is related to the amount of crystallization calorimetrically recorded. The effect of storage below the glass transition shows the possibility of a slow increase in nucleation below the glass transition, as already observed by other authors for different aqueous solutions. Isothermal crystallization is analyzed within the Johnson-Mehl-Avrami model for temperatures above -75°C. The corresponding samples have been cooled and warmed at the same rate of 40°C/min and calculations give, at constant nuclei numbers, an activation energy of 9.3 ± 0.3 kcal/mol and the Avrami exponent n = 2.2 ± 0.05. This shows a two-dimensional crystal growth as observed by cryomicroscopy. The estimated critical warming rate relevant to the preservation of rabbit kidneys by vitrification is 270°C/min with or without an increase in the nucleus density during storage. The present results support the possibility of using VS4 solution for vitrification of rabbit kidneys if pressure is not a limiting factor.

Identification of a high-affinity glycine betaine transport system in Staphylococcus aureus.

Staphylococcus aureus accumulates proline and glycine betaine when cells are grown at low water activity. In the present study, we have identified a high-affinity glycine betaine transport system in this bacterium. Optimal activity for this transport system was measured in the presence of high NaCl concentrations, but transport activity was not stimulated by high concentrations of other solutes.

A comparison of oxidation-reduction potentials calculated from the As(V)/As(III) and Fe(III)/Fe(II) couples with measured platinum-electrode potentials in groundwater

Oxidation-reduction (redox) potentials calculated from arsenic speciation showed fair correlation with measured Pt-electrode potentials (Eh) in shallow groundwaters in east-central Illinois. The observed bias in calculated potentials relative to measured Eh values could not be explained by analytical imprecision. Redox potentials calculated from Fe concentrations showed better correlation with measured potentials than the As potentials. Arsenic speciation may be a useful supplement to Eh measurements and concentrations of other solutes, but is probably not a good indicator of redox conditions when used alone.

Interpretation of the urine electrolytes and osmolality in the regulation of body fluid tonicity.

To evaluate urinary solutes in terms of their effect on body fluid tonicity, it is necessary to consider: whether that solute serves as an effective osmole in terms of ECF-ICF fluid shifts, its ability to accumulate in the body even if it is an osmotically effective particle, and the original number of body particles from which it derived. Thus, urea can be excluded since it is an ineffective osmole and only urine cations and anions need be considered. With respect to the former, one must separate the proportion of dietary versus endogenous potassium in this analysis as their effects differ. With respect to urine anions, urine chloride need not contribute to the loss of 'particles that count' when its excretion is accompanied by ammonium (i.e. equivalent to a bicarbonate gain). Thus, in the example cited at the beginning of this article, the excretion of hyperosmolar urine may not change body fluid tonicity if all the urinary potassium was of dietary origin and all the bicarbonate generated was retained as such. Finally, it is necessary to integrate defence of ECF volume (sodium balance), potassium balance, acid-base balance and intercompartmental fluid shifts to understand the overall renal response to defend tonicity. While there is utility in measuring urinary osmolality (assessment of medullary physiology, ADH action, water abstraction, concentrating power), in situations where body fluid tonicity is deranged, it is necessary to evaluate the urine sodium concentration along with the concentration of other solutes which may serve as effective osmoles in the urine.

Salt Tolerance in the Triticeae: Solute Accumulation and Distribution in an Amphidiploid derived fromTriticum aestivumcv. Chinese Spring andThinopyrum bessarabicum

An amphidiploid derived by colchicine treatment of a hybrid between Triticum aestivum cv Chinese Spring and Thinopyrum bessarabicum was found to be more salt tolerant than the wheat cultivars Chinese Spring, Kharchia and Ciano 79 in terms of survival and grain yield at 250 mol m−3 NaCl. Tolerance was related to the ability of the amphidiploid to exclude Na and Cl from the shoots, and particularly from the young leaves, developing inflorescence and grain. There was no relationship between the salt tolerance of the different species and varieties tested and changes in the concentrations of other solutes. The amphidiploid did not inherit the high glycinebetaine concentrations characteristic of the wheatgrass parent. Amphidiploids produced from crosses between Thinopyrum species and wheat may be useful as stress-resistant new crops.

Osmotic regulation of L-proline transport in Salmonella typhimurium.

The transport of proline is important for the adaptation of Salmonella typhimurium to osmotic stress because exogenous proline permits the growth of the organism in media of elevated osmotic strength that would otherwise be toxic. Measurements of the rate of [3H]proline transport in S. typhimurium indicated that the organism has two distinct proline permeases, the ProU and the ProP systems, whose activities increase more than fivefold as a consequence of growth in media containing 0.3 M NaCl or 0.47 M sucrose. Transport via a third proline permease, the PutP system, is not affected by the osmotic strength of the medium. We constructed strains that carry fusions of lacZ to proU or proP, genes that are required for the two osmotically stimulated proline transport systems. Assays of beta-galactosidase revealed that the transcription of the proU gene is increased more than 10-fold as a result of exposure of the cells to 0.3 M NaCl, 0.47 M sucrose, or equivalent concentrations of other solutes that are not freely diffusible across the cytoplasmic membrane. Increased transcription cannot be triggered by methanol, ethanol, and glycerol, substances that are freely diffusible across the membrane, suggesting that the signal for increased transcription might be an osmotic gradient across the cytoplasmic membrane. The proP gene does not show transcriptional regulation of sufficient magnitude to account for the stimulation of [3H]proline transport. Thus, the osmotic stimulation of the ProP system might be mediated by some posttranscriptional event.

The Role of Nitrate in the Osmoregulation of Lettuce (Lactuca sativaL.) Grown at Different Light Intensities

Blom-Zandstra, M. and Lampe, J. E. M., 1985. The role of nitrate in the osmoregulation of lettuce (Lactuca sativa L.) grown at different light intensities.—J. exp. Bot. 36: 1043-1052. The effect of different light intensities on the nitrate accumulation vis-a-vis the concentration of other solutes in plant sap expressed from lettuce leaves was studied. After growing lettuce plants under constant environmental conditions for 52 d, they were transferred to different light intensities and harvested periodically. A quantitative analysis of components in solution in the expressed plant sap showed a decrease in nitrate concentration and an increase in the organic acids (mainly malate) and sugars (mainly glucose) with increasing light intensity. The light intensity only slightly increased the osmolarity of the expressed plant sap. The measured osmolarity corresponded very well with the value estimated from the quantitative analyses implying that all osmotically active compounds had been accounted for. The decrease in nitrate concentration in the expressed plant sap was fully compensated for by an increase in the dissociated organic acids that partly dissociate twofold to sustain electroneutrality and by an increase in both organic acids and sugars to maintain the osmolarity. The suggestion is supported that nitrate may serve as osmoticum at low light conditions to compensate for the shortage of carbohydrates resulting from suboptimal photosynthesis.

On the mechanism of isosmotic transport across the small intestine. The composition of the absorbate transported from a mucosal solution made hypertonic by the addition of mannitol.

Experiments were performed to investigate the mechanism by which the fluid transported across the small intestine becomes isosmotic with the mucosal solution when the latter is made hypertonic by the addition of a poorly absorbed substance. The mid small intestine of the hamster was isolated and everted. The mucosal surface of the control preparation was bathed with an isotonic Krebs–Ringer bicarbonate solution containing 10 mM glucose (KRBSG) (292 mOsmol/kg). The mucosal surface of the experimental preparations was bathed with one of the hypertonic solutions. These hypertonic solutions were prepared by the addition of 1, 50, 100, or 150 mM mannitol to KRBSG. No bathing solution was placed on the serosal side of these preparations, so that the fluid transported across the intestine, undiluted by a bathing solution (absorbate), could be collected on the serosal side. Results show that the absorbate was always isosmotic with the mucosal solution. In the experimental preparations, as compared to the absorption of other solutes, mannitol was poorly absorbed, even though its concentration in the absorbate sometimes reached 35% of its concentration in the mucosal solution. The small amount of mannitol found in the absorbate was never sufficient to render the absorbates isosmotic with hypertonic mucosal solutions. The absorbate became isosmotic with the mucosal solution due to an increased concentration of other solutes transported from the mucosal side. Increasing the osmolality of the mucosal solution progressively from 292 to 442 mOsmol/kg caused a linear increase in the concentration of Na, K, glucose, and mannitol in the absorbate, but, except for mannitol, the net amount of these substances transported (per gram dry tissue) to the serosal side decreased linearly. The transport of fluid also decreased. Our data further indicate that the ratio of fluid and solute transport progressively decreased with the increase in osmolality of the mucosal solution. Therefore, it appears that when the mucosal solution is made hypertonic by the addition of a poorly absorbed substance, the absorbate becomes isosmotic with the hypertonic mucosal solution by means of a greater diminution of fluid transport than of solute transport.