Steady-state pH Research Articles

Kinetics of Estonian Phosphate Rock Dissolution in Hydrochloric Acid

The kinetics of the dissolution of Estonian phosphate rock and the governing reaction mechanisms in hydrochloric acid in technological processes were investigated. The influences of particle size and acid concentrations of 0.5–1.5 M on the reaction rate and the pH variation during the process were studied at a dosage of 2.1 moles of HCl per mole of calcium for 60 min. The results indicated that the solubility of phosphorus reached 94%–100% for the fine samples and 82%–99% for the coarse samples. The time required to achieve an apparent steady-state pH reduced with the increasing acid concentrations and decreasing particle sizes. It was determined that the CaF2 precipitation in solutions starting at 1 M was faster at higher concentrations. The SEM surface analysis of the insoluble particles proved the existence of etch pit formation. The XPS and EDX analyses affirmed that the dissolution was incongruent. The surface composition of the unreacted particles gave a stoichiometry of CaF1.8, showing the formation of CaF2 on the surface. The dissolution kinetics were analyzed using the shrinking core model and showed a combination of chemical reaction, diffusion or interfacial transfer, and diffusion, sequentially for coarse particles or simultaneously for fine fractions.

Catalytic Proton-Hydroxide Recombination for Forward-Bias Bipolar Membranes

Bipolar membranes (BPMs) uniquely generate steady state pH gradients in electrochemical cells, enabling half reactions to occur efficiently in different pH environments, and are thus of broad interest. Forward-bias BPMs further enable new fuel-cell, redox-flow batteries, and CO2-electrolyzer concepts. In forward bias, the gradient in electrochemical potential drives ionic charge carriers toward the bipolar junction where they can recombine. We use a H2-pump electrochemical cell to study H+ / OH− recombination at the bipolar junction. We discover that metal oxide nanoparticles substantially catalyze the recombination reaction in the bipolar junction under forward bias and find evidence that H+ / OH− recombination occurs via a surface mechanism on the oxide catalyst. We propose a rate equation to describe the catalytic H+ / OH− recombination mechanism, supported by numerical simulations. Membrane sensing experiments further reveal the nature of the oxide catalyst layers and provide insight into the potential and temperature dependence of H+ / OH− recombination at the bipolar junction. This work thus elucidates materials-design strategies for recombination catalysts to advance forward-bias BPM technologies.

Evolution of the theoretical description of the isoelectric focusing experiment: II. An open system isoelectric focusing experiment is a transient, bidirectional isotachophoretic experiment.

The carrier ampholytes-based (CA-based) isoelectric focusing (IEF) experiment evolved from Svensson's closed system IEF (constant spatial current density, absence of convective mixing, counter-balancing electrophoretic and diffusive fluxes yielding a steady state pH gradient) to the contemporary open system IEF (absence of convective mixing, large cross-sectional area electrode vessels, lack of counter-balancing electrophoretic- and diffusive fluxes leading to transient pH gradients). Open system IEF currently is described by a two-stage model: In the first stage, a rapid IEF process forms the pH gradient which, in the second stage, is slowly degraded by isotachophoretic processes that move the most acidic and most basic CAs into the electrode vessels. An analysis of the effective mobilities and the effective mobility to conductivity ratios of the anolyte, catholyte, and the CAs indicates that in open system IEF experiments a single process, transient bidirectional isotachophoresis (tbdITP) operates from the moment current is turned on until it is turned off. In tbdITP, the anolyte and catholyte provide the leading ions and the pI 7 CA or the reactive boundary of the counter-migrating H3 O+ and OH- ions serves as the shared terminator. The outcome of the tbdITP process is determined by the ionic mobilities, pKa values, and loaded amounts of all ionic and ionizable components: It is constrained by both the transmitted amount of charge and the migration space available for the leading ions. tbdITP and the resulting pH gradient can never reach steady state with respect to the spatial coordinate of the separation channel.

Evolution of the theoretical description of the isoelectric focusing experiment: III. Carrier ampholyte behavior in transient, bidirectional isotachophoresis.

In modern isoelectric focusing (IEF) systems, where (i) convective mixing is prevented by gels or small cross-sectional area separation channels, (ii) current densities vary spatially due to the presence of electrode vessels with much larger cross-sectional areas than those of the gels or separation channels, and (iii) electrophoretic and diffusive fluxes do not balance each other, stationary, steady-state pH gradients cannot form (open-system IEF). Open-system IEF is currently described as a two-stage process: A rapid IEF process forms the pH gradient from the carrier ampholytes (CAs) in the first stage, then isotachophoretic processes degrade the pH gradient in the second stage as the extreme pI CAs are moved into the electrode vessels where they become diluted. Based on the ratios of the local effective mobilities and the local conductivities ( / values) of the anolyte, catholyte, and the CAs, we pointed out in the preceding paper (Vigh G, Gas B, Electrophoresis 2023, 44, 675-88) that in open-system IEF, a single process, transient, bidirectional isotachophoresis (tbdITP) operates from the moment current is turned on. In this paper, we demonstrate some of the operational features of the tbdITP model using the new ITP/IEF version of Simul 6.

A microfluidic double emulsion platform for spatiotemporal control of pH and particle synthesis.

The temporal control of pH in microreactors such as emulsion droplets plays a vital role in applications including biomineralisation and microparticle synthesis. Typically, pH changes are achieved either by passive diffusion of species into a droplet or by acid/base producing reactions. Here, we exploit an enzyme reaction combined with the properties of a water-oil-water (W/O/W) double emulsion to control the pH-time profile in the droplets. A microfluidic platform was used for production of ∼100-200 μm urease-encapsulated double emulsions with a tuneable mineral oil shell thickness of 10-40 μm. The reaction was initiated on-demand by addition of urea and a pulse in base (ammonia) up to pH 8 was observed in the droplets after a time lag of the order of minutes. The pH-time profile can be manipulated by the diffusion timescale of urea and ammonia through the oil layer, resulting in a steady state pH not observed in bulk reactive solutions. This approach may be used to regulate the formation of pH sensitive materials under mild conditions and, as a proof of concept, the reaction was coupled to calcium phosphate precipitation in the droplets. The oil shell thickness was varied to select for either brushite microplatelets or hydroxyapatite particles, compared to the mixture of different precipitates obtained in bulk.

Catalytic Proton–Hydroxide Recombination for Forward-Bias Bipolar Membranes

Bipolar membranes (BPMs) can generate steady-state pH gradients in electrochemical cells, enabling half-reactions to occur in different pH environments, and are thus of broad interest. Forward-bias BPMs further enable new approaches to fuel cells, redox-flow batteries, and CO2 electrolyzers. In forward bias, the gradient in electrochemical potential drives ionic charge carriers toward the bipolar junction where they can recombine. We use a H2-pump electrochemical cell to study H+/OH– recombination at the bipolar junction. We discover that metal-oxide nanoparticles catalyze the recombination reaction in the bipolar junction under forward bias and find evidence that H+/OH– recombination occurs via a surface mechanism on the oxide catalyst. We propose a rate equation to describe the catalytic H+/OH– recombination mechanism, supported by numerical simulations. This work thus elucidates materials-design strategies for recombination catalysts to advance forward-bias BPM technologies.

Insights from electrochemical crack tip modeling of atmospheric stress corrosion cracking

Crack tip electrochemical conditions are explored utilizing a reactive transport Finite Element Method model for stainless steel 304 exposed to 3 M NaCl. Under simulated full immersion conditions, a steady state pH of 3 and metal chloride concentration of 1.4 M were calculated. It was determined that an increase in cathode length and a decrease in water layer thickness increases total cathodic current per unit thickness, metal chloride concentrations, and decreases crack tip pH. The presented results and discussion call into question whether electrochemical similitude is achieved between different specimens, crack lengths, and between laboratory specimen and field relevant samples.

Effect of the steady-state pH of kaolinite pore fluid on its microstructure and geotechnical properties

Effect of the steady-state pH of kaolinite pore fluid on its microstructure and geotechnical properties

High-performance bipolar membrane for electrochemical water electrolysis

A bipolar membrane (BPM) enables the dissociation of water into protons and hydroxide ions, which in-situ maintains a steady-state pH difference in electrochemical water electrolyzers for optimum electro-kinetics of the anode and cathode electrocatalysts. However, instability and high overpotential requirement of the commercial Fumasep BPMs to drive water dissociation (ηWD > 100 mV at 20 mA cm−2) are major challenges to successfully applying them in electrochemical devices. To circumvent these membrane issues, we present the electrostatic self-assembly strategy to construct Fe(OH)3 colloids-based catalytic layer (FCL), which enhances the internal electric field, necessary to boost the polarization process of water molecules. Kelvin Probe Force Microscopy (KPFM) also confirms the improved work function (WF) of the FCL to establish a stronger built-in electric field for a fast polarization process during water dissociation. Consequently, the fabricated Fe(OH)3 colloids-based BPMs (FCBMs) require very little ηWD (29 mV) than commercial Fumasep BPM (ηWD: 44 mV) at 20 mA cm−2, which indicates the energy-efficient operability of the FCBMs in electrochemical water electrolyzers. This work demonstrates an effective route to fabricate stable and energy-efficient BPMs, ready to install in advanced acid-alkaline water electrolysis systems for significantly enhanced hydrogen generation efficiency.

Quantitative Analysis of Presynaptic Vesicle Luminal pH in Cultured Neurons.

Newly generated synaptic vesicles (SVs) are re-acidified by the activity of the vacuolar-type H+-ATPases. Since H+ gradient across SV membrane drives neurotransmitter uptake into SVs, precise measurements of steady-state vesicular pH and dynamics of re-acidification process will provide important information concerning the H+-driven neurotransmitter uptake. Indeed, we recently demonstrated distinct features of steady state and dynamics of vesicular pH between glutamatergic vesicles and GABAergic vesicles in cultured hippocampal neurons. In this article, we focus on an experimental protocol and setup required to determine steady-state luminal pH of SVs in living neurons. This protocol is composed of efficient expression of a pH-sensitive fluorescent protein in the lumen of SVs in cultured neurons, and recordings of its fluorescence changes under a conventional fluorescent microscope during local applications of acidic buffer and ionophores-containing solution at a given pH. The method described here can be easily applied for measuring luminal pH of different types of secretory organelles and other acidic organelles such as lysosomes and endosomes in cultured cell preparations.

(Invited) Ambient Storage and Washing of NCMs: Formation/Removal of Surface Contaminants and NCM Structural Changes upon Heating of Washed/Stored NCMs

Cathode active materials (CAMs) based on Ni-rich layered transition metal oxides, like NCMs or NCAs, are commonly subjected to a final washing step in water to remove residual lithium hydroxide and carbonate, which otherwise lead to gelling of the electrode slurry and gassing during cell operation [1,2]. Washing, however, is accompanied by an increase in the pH of the washing solution (the steady-state pH increasing with Ni content), suggesting a Li+/H+ exchange in the near-surface region of the CAM particles, concomitant with the formation LiOH [3,4]. Due to the latter, small amounts of OH-based surface contaminants remain on the surface after washing, while carbonate-based surface contaminants can be removed completely, as shown by XPS [5]. TGA-MS analysis reveals that the incorporation of protons in washed NCMs results in a mass loss at much lower temperatures than in the case of pristine lithiated NCMs; it is accompanied by the release of H2O at ~160 °C and of O2 at ~270 °C, which are ascribed to the formation of spinel- and rocksalt-like surface phases, respectively [3]. These surface processes may be compared to the bulk conversion of layered nickel oxyhydroxide (NiOOH) to the NiO rocksalt phase that initiates at also »160 °C upon the simultaneous release of H2O and O2 [6]. The formation of these oxygen-depleted surface phases can also be confirmed by XPS and soft-XAS [5, 7] and they result in a significant increase of the CAM impedance [3].The Li+/H+ exchange in the near-surface region of layered transition metal oxide CAMs upon washing was also shown to occur upon their storage at humid ambient air [5]. In this case, however, surface contaminants are accumulated on the CAM surface, consisting of LiOH, Li2CO3, and basic nickel carbonates (NiCO3·2Ni(OH)2·xH2O) [8,9,10]. The total amount of these surface contaminants increases with storage time and particularly with Ni content [5], leading to a deterioration of their cycling performance [8,9,10], which we have ascribed to their high reactivity with the electrolyte [10]. Upon heating of NCMs stored at humid air, surface contaminants other than Li2CO3 can be removed up to 450 °C, while the Li+/H+ exchange leads to the formation of oxygen-depleted surface layers within the same temperature range, identical to what was observed for washed NCMs.This presentation will review and summarize the above described phenomena, outlining the differences and the similarities between the NCM surface changes affected by either washing or storage at ambient humid air.

Bipolar Membrane and Interface Materials for Electrochemical Energy Systems

Bipolar membranes (BPMs) are recently emerging as a promising material for application in advanced electrochemical energy systems such as (photo)electrochemical CO2 reduction and water splitting. BPMs exhibit a unique property to accelerate water dissociation and ionic separation that allows for maintaining a steady-state pH gradient in electrochemical devices without a significant loss in process efficiency, thereby allowing a broader catalyst material selection for the respective oxidation and reduction reactions. However, the formation of high-performance BPMs with significantly reduced overpotentials for driving water dissociation and ionic separation at conditions and rates that are relevant to energy technologies is a key challenge. Herein, we perform a detailed assessment of the requirements in base materials and optimal design routes for the BPM layer and interface formation. In particular, the interface in the BPM presents a critical component with its structure and morphology influencing the kinetics of water dissociation reaction governed by both electric field and catalyst driven mechanisms. For this purpose, we present, among others, the advantages and drawbacks in the utilization of a bulk heterojunction formed in 3D structures that recently have been reported to demonstrate a possibility of designing stable and high-performance BPMs. Also, the outer layers of a BPM play a crucial role in kinetics and mass transport, particularly related to water and ion transport at electrolyte-membrane and membrane-catalyst interfaces. This work aims at identifying the gaps in the structure-property of the current monopolar materials to provide prospective facile design routes for BPMs with excellent water dissociation and ionic separation efficiency. It extends to a discussion about material selection and design strategies of advanced BPMs for application in emerging electrochemical energy systems.

Dissolution Rates of Allophane With Variable Fe Contents: Implications for Aqueous Alteration and the Preservation of X-Ray Amorphous Materials on Mars

AbstractRecent measurements from Mars document X-ray amorphous/nano-crystalline materials in multiple locations across the planet. Despite their prevalence, however, little is known about these materials or what their presence implies for the history of Mars. The X-ray amorphous component of the martian soil in Gale crater has an X-ray diffraction pattern that can be fit partially with allophane (approximately Al2O3⋅(SiO2)1.3–2⋅(H2O)2.5–3), and the low-temperature water-release data are consistent with allophane. The chemical data from Gale crater suggest that other silicate materials similar to allophane, such as Fe-substituted allophane (approximately (Fe2O3)0.01–0.5(Al2O3)0.5–0.99⋅(SiO2)2⋅3H2O), may also be present. In order to investigate the properties of these potential poorly crystalline components of the martian soil, Fe-free allophane (Fe:Al = 0), Fe-poor allophane (Fe:Al = 1:99), and Fe-rich allophane (Fe:Al = 1:1) were synthesized and then characterized using electron microscopy and Mars-relevant techniques, including infrared spectroscopy, X-ray diffraction, and evolved gas analysis. Dissolution experiments were performed under acidic (initial pH values pH0 = 3.01, pH0 = 5.04), near-neutral (pH0 = 6.99), and alkaline (pH0 = 10.4) conditions in order to determine dissolution kinetics and alteration phases for these poorly crystalline materials. Dissolution rates (rdiss), based on the rate of Si release into solution, show that these poorly crystalline materials dissolve approximately an order of magnitude faster than crystalline phases with similar compositions at all pH conditions. For Fe-free allophane, logrdiss = –10.65–0.15 × pH; for Fe-poor allophane, logrdiss = –10.35–0.22 × pH; and for Fe-rich allophane, logrdiss = –11.46–0.042 × pH at 25°C, where rdiss has the units of mol m–2 s–1. The formation of incipient phyllosilicate-like phases was detected in Fe-free and Fe-rich allophane reacted in aqueous solutions with pH0 = 10.4 (steady-state pH ≈ 8). Mars-analog instrument analyses demonstrate that Fe-free allophane, Fe-poor allophane, and Fe-rich allophane are appropriate analogs for silicate phases in the martian amorphous soil component. Therefore, similar materials on Mars must have had limited interaction with liquid water since their formation. Combined with chemical changes expected from weathering, such as phyllosilicate formation, the rapid alteration of these poorly crystalline materials may be a useful tool for evaluating the extent of aqueous alteration in returned samples of martian soils.

Calcineurin homologous protein isoform 2 supports tumor survival via the sodium hydrogen exchanger isoform 1 in non-small cell lung cancer.

Maintaining intracellular pH is crucial for preserving healthy cellular behavior and, when dysregulated, results in increased proliferation, migration, and invasion. The Na+/H+ exchanger isoform 1 is a highly regulated transmembrane antiporter that maintains pH homeostasis by exporting protons in response to intra- and extracellular signals. Activation of Na+/H+ exchanger isoform 1 is exquisitely regulated by the extracellular environment and protein cofactors, including calcineurin B homologous proteins 1 and 2. While Na+/H+ exchanger isoform 1 and calcineurin B homologous protein 1 are ubiquitously expressed, calcineurin B homologous protein 2 shows tissue-specific expression and upregulation in a variety of cancer cells. In addition, calcineurin B homologous protein 2 expression is modulated by tumorigenic extracellular conditions like low nutrients. To understand the role of calcineurin B homologous protein 2 in tumorigenesis and survival in lung cancer, we surveyed existing databases and formed a comprehensive report of Na+/H+ exchanger isoform 1, calcineurin B homologous protein 1, and calcineurin B homologous protein 2 expression in diseased and non-diseased tissues. We show that calcineurin B homologous protein 2 is upregulated during oncogenesis in many adeno and squamous carcinomas. To understand the functional role of calcineurin B homologous protein 2 upregulation, we evaluated the effect of Na+/H+ exchanger isoform 1 and calcineurin B homologous protein 2 depletion on cellular function during cancer progression in situ. Here, we show that calcineurin B homologous protein 2 functions through Na+/H+ exchanger isoform 1 to effect cell proliferation, cell migration, steady-state pHi, and anchorage-independent tumor growth. Finally, we present evidence that calcineurin B homologous protein 2 depletion in vivo has potential to reduce tumor burden in a xenograft model. Together, these data support the tumor-promoting potential of aberrant calcineurin B homologous protein 2 expression and position calcineurin B homologous protein 2 as a potential therapeutic target for the treatment of non-small cell lung cancer.

Studying Proton Gradients Across the Nuclear Envelope.

The existence of nuclear pore complexes in the nuclear envelope has led to the assumption that ions move freely from the cytosol into the nucleus, and that the molecular mechanisms at the plasma membrane that regulate cytosolic pH also regulate nuclear pH. Furthermore, studies to measure pH in the nucleus have produced contradictory results, since it has been found that the nuclear pH is either similar to the cytosol or more alkaline than the cytosol. However, most studies of nuclear pH have lacked the rigor needed to understand pH regulation in the nucleus. A major problem has been the lack of in situ titrations in the nucleus and cytosol, since the intracellular environment is different in the cytosol and nucleus and the behavior of fluorescent pH probes is different in these environments. Here we present a method that uses the fluorescence of SNARF-1 that labels both cytosol and nucleus. Using ratio imaging microscopy, regions of interest corresponding to the nucleus and cytosol to perform steady-state pH measurements followed by in situ titrations, tocorrectly assign pH in those cellular domains.

Modifying the dewatering behaviour of iron solids from ferric sulphate solutions during lime treatment

In the continuous lime neutralization treatment of iron-laden wastewaters, such as acid mine drainage (AMD), the solid-liquid separation of iron solids formed is difficult to effect. The particle formation mechanisms, the ensuing particle size and size distribution – which in turn shape the dewatering process – are strongly influenced by the OH/Fe molar feed ratios since they dictate the supersaturation level. This work describes tests using a stoichiometric and sub- stoichiometric OH/Fe molar ratio (R = 3 and 2.5 respectively) to establish settleability and filterability variations of a slurry precipitated at steady state in a mixed-suspension-mixed-product-removal (MSMPR) reactor at 15 min residence time. Three initial ferric concentrations ([Fe(III)]) of 100, 300 and 800 mg/L were used. The results revealed that particle-particle repulsion and product dewatering characteristics were dependent on the relationship between supersaturation, pH and ionic strength. The best product performance, as seen in fastest settling rate of 3.3 ± 0.2 mm/min, an increase in the filtration rate from 3.7 ± 0.4 to 5.1 ± 0.5 cm3/cm2 min and a decrease in the specific resistance to filtration (SRF) from 1.42 × 1012 to 6.71 × 1011 m/ kg, was observed for particles formed at R = 2.5 and a [Fe(III)] of 300 mg/L. The product performance was attributed to reduced supersaturation and minimal particle-particle repulsion due to the proximity of the steady state pH and point of zero charge. This favoured a neutral surface charge resulting in the dominance of large (D4,3 of 48.3 ± 0.05 μm and D3,2 of 30.8 ± 0.05 μm), regular shaped agglomerates which had a narrow, unimodal distribution and a notable decrease in the peak number of fine particles from 3.5 × 1013 to 1.7 × 1012 / m3. Sub- stoichiometric molar ratios produced insignificant filterability changes at [Fe(III)] of 100 and 800 mg/L but the latter showed significant settling rate changes (the largest change of threefold - from 0.8 to 2.4 ± 0.2 mm/min). These results suggest that AMD treatment plants that employ lime neutralization should be operated at lower OH concentrations than is the current practice, as this ensures improved iron removal as well as settling and filtration properties of the sludge. This may have the added benefit of decreased neutralization costs as less lime will be required.

Differential pH Dynamics in Synaptic Vesicles From Intact Glutamatergic and GABAergic Synapses.

Synaptic transmission requires the presynaptic release of neurotransmitter from synaptic vesicles (SVs) onto the postsynaptic neuron. Vesicular neurotransmitter transporter proteins, which use a V-ATPase-generated proton gradient, play a crucial role in packaging neurotransmitter into SVs. Recent work has revealed different proton dynamics in SVs expressing the vesicular glutamate transporter (VGLUT) or the vesicular GABA transporter (VGAT) proteins. At the whole synapse level, this results in different steady-state pH and different reacidification dynamics during SV recycling (Egashira et al., 2016). In isolated SVs, the presence of VGAT causes a higher steady state pH, which is correlated with a faster proton efflux rate (Farsi et al., 2016). To address whether proton efflux from GABAergic and glutamatergic SVs in intact synapses differs, we applied a glutamatergic- or GABAergic neuron-specific expression strategy (Chang et al., 2014) to express a genetically encoded pH sensor (synaptophysin pHluorin; SypHy) and/or light-activated proton pump (pHoenix; (Rost et al., 2015). We confirm, with SypHy post-stimulation fluorescence dynamics, that the pH profile of recycling GABAergic SVs differs from that of recycling glutamatergic SVs (Egashira et al., 2016). Using light-activation of pHoenix in pH-neutral vesicles, we investigated the pH dynamics of actively filling vesicles, and could show that proton efflux from GABAergic SVs is indeed initially faster than glutamatergic SVs in intact synapses. Finally, we compared the filling rate of empty glutamatergic and GABAergic vesicles using pHoenix as a proton source, and find a slightly faster filling of glutamatergic vs. GABAergic SVs.

The effect of Fe(III) concentration on the dewatering behaviour of Fe(III) oxyhydroxide precipitates from low-tenor solutions

The settling and dewatering of sludge are critical steps in the lime precipitation treatment of iron rich wastewaters, such as acid mine drainage (AMD). This fundamental study describes the effect of different ferric feed concentrations ([Fe(III)]: 50 to 800 mg/L) on the dewatering behaviour of the sludge precipitated under steady state conditions and high pH (9 to 11), as measured through filterability and settleability. Experiments were conducted in an agitated mixed-suspension-mixed-product-removal (MSMPR) reactor in which Fe2(SO4)3 and Ca(OH)2 were added as the Fe(III) and OH– sources, respectively, and the product was collected for analysis from the overflow. Reaction conditions were such that no gypsum was precipitated. The results indicate that the Fe(III) in the feed influenced the dewatering behaviour of the precipitation product, via particle size, particle size distribution (PSD), surface charge, morphology and structure. Particles formed at 300 mg/L exhibited increased size with a maximum D4,3 of 27 μm, a narrow PSD characterized by a span of 1.65, a specific resistance to filtration (SRF) of 1.42 × 1012 m/kg and a zeta potential of approximately 0 mV. These conditions resulted in enhanced agglomeration and better settling behaviour, although the filtering behaviour was not improved. This dewatering behaviour was attributed to a dense network of interlocked and interconnected bridges in the bulk morphology of the particles as evidenced by image analysis results. The steady state pH and Fe(III) conversion in the reactor were also influenced by the feed [Fe(III)] changes. The results show scope for potentially better solid-liquid separation in iron precipitation processes through controlling feed [Fe(III)].

Secondary Response to Chronic Respiratory Acidosis in Humans: A Prospective Study

IntroductionThe magnitude of the secondary response to chronic respiratory acidosis, that is, change in plasma bicarbonate concentration ([HCO3−]) per mm Hg change in arterial carbon dioxide tension (PaCO2), remains uncertain. Retrospective observations yielded Δ[HCO3−]/ΔPaCO2 slopes of 0.35 to 0.51 mEq/l per mm Hg, but all studies have methodologic flaws.MethodsWe studied prospectively 28 stable outpatients with steady-state chronic hypercapnia. Patients did not have other disorders and were not taking medications that could affect acid−base status. We obtained 2 measurements of arterial blood gases and plasma chemistries within a 10-day period.ResultsSteady-state PaCO2 ranged from 44.2 to 68.8 mm Hg. For the entire cohort, mean (± SD) steady-state plasma acid−base values were as follows: PaCO2, 52.8 ± 6.0 mm Hg; [HCO3−], 29.9 ± 3.0 mEq/l, and pH, 7.37 ± 0.02. Least-squares regression for steady-state [HCO3−] versus PaCO2 had a slope of 0.476 mEq/l per mm Hg (95% CI = 0.414–0.538, P < 0.01; r = 0.95) and that for steady-state pH versus PaCO2 had a slope of −0.0012 units per mm Hg (95% CI = −0.0021 to −0.0003, P = 0.01; r = −0.47). These data allowed estimation of the 95% prediction intervals for plasma [HCO3−] and pH at different levels of PaCO2 applicable to patients with steady-state chronic hypercapnia.ConclusionIn steady-state chronic hypercapnia up to 70 mm Hg, the Δ[HCO3−]/ΔPaCO2 slope equaled 0.48 mEq/l per mm Hg, sufficient to maintain systemic acidity between the mid-normal range and mild acidemia. The estimated 95% prediction intervals enable differentiation between simple chronic respiratory acidosis and hypercapnia coexisting with additional acid−base disorders.

KCC2-dependent Steady-state Intracellular Chloride Concentration and pH in Cortical Layer 2/3 Neurons of Anesthetized and Awake Mice.

Neuronal intracellular Cl− concentration ([Cl−]i) influences a wide range of processes such as neuronal inhibition, membrane potential dynamics, intracellular pH (pHi) or cell volume. Up to date, neuronal [Cl−]i has predominantly been studied in model systems of reduced complexity. Here, we implemented the genetically encoded ratiometric Cl− indicator Superclomeleon (SCLM) to estimate the steady-state [Cl−]i in cortical neurons from anesthetized and awake mice using 2-photon microscopy. Additionally, we implemented superecliptic pHluorin (SE-pHluorin) as a ratiometric sensor to estimate the intracellular steady-state pH (pHi) of mouse cortical neurons in vivo. We estimated an average resting [Cl−]i of 6 ± 2 mM with no evidence of subcellular gradients in the proximal somato-dendritic domain and an average somatic pHi of 7.1 ± 0.2. Neither [Cl−]i nor pHi were affected by isoflurane anesthesia. We deleted the cation-Cl− co-transporter KCC2 in single identified neurons of adult mice and found an increase of [Cl−]i to approximately 26 ± 8 mM, demonstrating that under in vivo conditions KCC2 produces low [Cl−]i in adult mouse neurons. In summary, neurons of the brain of awake adult mice exhibit a low and evenly distributed [Cl−]i in the proximal somato-dendritic compartment that is independent of anesthesia and requires KCC2 expression for its maintenance.