Rate Of pH Change Research Articles

The effect of conditioning pH behaviour on spodumene flotation with fatty acids

ABSTRACT Spodumene - the primary lithium mineral - is often concentrated by flotation with fatty acid collectors. However, producing high-grade concentrates at high recoveries is challenging and a risk for future operations. Poor spodumene selectivity is largely driven by the sensitive properties and poor solubility of fatty acids and requires high-density conditioning for desired flotation performance. This study related pH behaviour and operating parameters during fatty acid conditioning to flotation performance. The best pH characteristics for >85% lithium recovery at >5.25% Li2O were a minimum pH 6.5–6.8, final pH 6.7–7.1, and a pH change rate of 0.07 ΔpH/min. Regression analysis predicted optimizated conditions of initial pH 8.2, 30 W/L power density, 8 min conditioning and 550 g/t collector. Follow-up testing confirmed a higher W/L improved grade, and recovery was maintained when combined with decreased residence time and pH. Better defining these relationships can improve process control n developing industrial spodumene flotation circuits.

Re-evaluating fetal scalp pH thresholds: An examination of fetal pH variations during labor.

Since the 1970s, fetal scalp blood sampling (FSBS) has been used as a second-line test of the acid-base status of the fetus to evaluate fetal well-being during labor. The commonly employed thresholds that delineate normal pH (>7.25), subnormal (7.20-7.25), and pathological pH (<7.20) guide clinical decisions. However, these experienced-based thresholds, based on observations and common sense, have yet to be confirmed. The aim of the study was to investigate if pH drop rate accelerates at the common thresholds (7.25 and 7.20) and to explore the possibility of identifying more accurate thresholds. A retrospective study was conducted at a tertiary maternity hospital between June 2017 and July 2021. Patients with at least one FSBS during labor for category II fetal heart rate and delivery of a singleton cephalic infant were included. The rate of change in pH value between consecutive samples for each patient was calculated and plotted as a function of pH value. Linear regression models were used to model the evolution of the pH drop rate estimating slope and standard errors across predefined pH intervals. Exploration of alternative pH action thresholds was conducted. To explore the independence of the association between pH value and pH drop rate, multiple linear regression adjusted on age, body mass index, parity, oxytocin stimulation and suspected small for gestational age was performed. We included 2047 patients with at least one FSBS (total FSBS 3467); with 2047 umbilical cord blood pH, and a total of 5514 pH samples. Median pH values were 7.29 1 h before delivery, 7.26 30 min before delivery. The pH drop was slow between 7.40 and 7.30, then became more pronounced, with median rates of 0.0005 units/min at 7.25 and 0.0013 units/min at 7.20. Out of the alternative pH thresholds, 7.26 and 7.20 demonstrated the best alignment with our dataset. Multiple linear regression revealed that only pH value was significantly associated to the rate of pH change. Our study confirms the validity and reliability of current guideline thresholds for fetal scalp pH in category II fetal heart rate.

Controlled Annealing in Adaptive Multicomponent Gels

AbstractWe use a pH‐driven annealing process to convert between co‐assembled and self‐sorted networks in multicomponent gels. The initially formed gels at low pH are co‐assembled, with the two components coexisting within the same self‐assembled structures. We use an enzymatic approach to increase the pH, resulting in a gel‐to‐sol transition, followed by a hydrolysis to lower the pH once again. As the pH decreases, a self‐sorted network is formed by a two‐stage gelation process determined by the pKaof each component. This approach can be expanded to layered systems to generate many varied systems by changing composition and rates of pH change, adapting their microstructure and so allowing access to a far greater range of morphologies and complexity than can be achieved in single component systems.

Controlled Annealing in Adaptive Multicomponent Gels.

We use a pH-driven annealing process to convert between co-assembled and self-sorted networks in multicomponent gels. The initially formed gels at low pH are co-assembled, with the two components coexisting within the same self-assembled structures. We use an enzymatic approach to increase the pH, resulting in a gel-to-sol transition, followed by a hydrolysis to lower the pH once again. As the pH decreases, a self-sorted network is formed by a two-stage gelation process determined by the pKa of each component. This approach can be expanded to layered systems to generate many varied systems by changing composition and rates of pH change, adapting their microstructure and so allowing access to a far greater range of morphologies and complexity than can be achieved in single component systems.

Toward Rapid and Automated Immunoassays: Using a Localized Electrochemical pH Modulation Platform to Perform a Single-Step Immunoassay.

An electrochemical platform for generating and controlling a localized pH microenvironment on demand is proposed by employing a closed-loop control algorithm based on an iridium oxide pH sensor input. We use a combination of solution-borne quinones and galvanostatic excitation on a prepatterned indium tin oxide (ITO) working electrode to modulate pH within a very well confined, small volume of solution close to the electrode surface. We demonstrate that the rate of pH change can be controlled at up to 2 pH s-1 with an excellent repeatability (±0.004). The desired pH microenvironment can be stably maintained for longer than 2 h within ±0.0012 pH. As a high-impact application of the platform technology, we propose a single-step immunoassay and demonstrate its utility in measuring C-reactive protein (CRP), a critical inflammatory marker in various conditions such as myocardial infarction and even SARS-Cov-2. Utilizing pH modulation technology along with pH-sensitive fluorescence dye simplifies the immunoassay process into a single-step, where a mixture of all of the reagents is incubated only for 1 h without any washing steps or the need to change solution. This simplified immunoassay process minimizes the hands-on time of the end-user and thus decreases technician-driven errors. Moreover, the absence of complicated liquid-handling hardware makes it more suitable and attractive for an ultracompact platform to ultimately be used in a point-of-care diagnostic assay.

Technical note: Stability of tris pH buffer in artificial seawater stored in bags

Abstract. Equimolal tris (2-amino-2-hydroxymethyl-propane-1,3-diol) buffer in artificial seawater is a well characterized and commonly used standard for oceanographic pH measurements. We evaluated the stability of tris pH when stored in purportedly gas-impermeable bags across a variety of experimental conditions, including bag type and storage in air vs. seawater over 300 d. Bench-top spectrophotometric pH analysis revealed that the pH of tris stored in bags decreased at a rate of 0.0058±0.0011 yr−1 (mean slope ±95 % confidence interval of slope). The upper and lower bounds of expected pH change at t=365 d, calculated using the averages and confidence intervals of slope and intercept of measured pH change vs. time data, were −0.0042 and −0.0076 from initial pH. Analyses of total dissolved inorganic carbon confirmed that a combination of CO2 infiltration and/or microbial respiration led to the observed decrease in pH. Eliminating the change in pH of bagged tris remains a goal, yet the rate of pH change is lower than many processes of interest and demonstrates the potential of bagged tris for sensor calibration and validation of autonomous in situ pH measurements.

Preliminary Study of Ozonated Water to Preserve the Quality of Tofu: The Effect of Exposure Time and Replacement of Ozonated Water

Tofu is a very popular source of vegetable protein in Indonesia. However, tofu is a very perishable food type because its water content is also very high and high in protein. Ozonated water is one of many solutions to preserve the quality of tofu. Ozone is an anti-microbial agent and is already recognized as safe to be contacted with food. This research aims to see the effect of exposure time and replacement of ozonated water in preserving tofu’s quality. The quality parameters that are observed in this research are total mesophilic aerobic bacteria (TMAB), pH, and protein level. The tofu is exposed to ozonated water (0.32 mg O3/L) for 40, 80, and 120 minutes. For water replacement, tofu is exposed to ozonated water (0.32 mg O3/L) for 120 minutes, and the water replacement occurred every 40 and 60 minutes (unreplaced water is observed as well). One hundred twenty minutes exposure can disinfect 51% TMAB and suppress the rate of change in pH and protein level in tofu. Moreover, water replacement every 40 minutes can disinfect 96% TMAB and suppress the rate of change of pH and protein level. This research shows that replacing ozonated water every 40 minutes is the most effective treatment among others in preserving the quality of tofu.

Directed Evolution of a Glutathione Transferase for the Development of a Biosensor for Alachlor Determination

In the present work, DNA recombination of three homologous tau class glutathione transferases (GSTUs) allowed the creation of a library of tau class GmGSTUs. The library was activity screened for the identification of glutathione transferase (GST) variants with enhanced catalytic activity towards the herbicide alachlor (2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide). One enzyme variant (GmGSTsf) with improved catalytic activity and binding affinity for alachlor was identified and explored for the development of an optical biosensor for alachlor determination. Kinetics analysis and molecular modeling studies revealed a key mutation (Ile69Val) at the subunit interface (helix α3) that appeared to be responsible for the altered catalytic properties. The enzyme was immobilized directly on polyvinylidenefluoride membrane by crosslinking with glutaraldehyde and was placed on the inner surface of a plastic cuvette. The rate of pH changes observed as a result of the enzyme reaction was followed optometrically using a pH indicator. A calibration curve indicated that the linear concentration range for alachlor was 30–300 μM. The approach used in the present study can provide tools for the generation of novel enzymes for eco-efficient and environment-friendly analytical technologies. In addition, the outcome of this study gives an example for harnessing protein symmetry for enzyme design.

Global trends of ocean CO2 sink and ocean acidification: an observation-based reconstruction of surface ocean inorganic carbon variables

Ocean acidification is likely to impact marine ecosystems and human societies adversely and is a carbon cycle issue of great concern. Projecting the degree of ocean acidification and the carbon-climate feedback will require understanding the current status, variability, and trends of ocean inorganic carbon system variables and the ocean carbon sink. With this goal in mind, we reconstructed total alkalinity (TA), dissolved inorganic carbon (DIC), CO2 partial pressure (pCO2sea), sea–air CO2 flux, pH, and aragonite saturation state (Ωarg) for the global ocean based on measurements of pCO2sea and TA. We used a multiple linear regression approach to derive relationships to explain TA and DIC and obtained monthly 1° × 1° gridded values of TA and DIC for the period 1993–2018. These data were converted to pCO2sea, pH, and Ωarg, and monthly sea-air CO2 fluxes were obtained in combination with atmospheric CO2. Mean annual sea–air CO2 flux and its rate of change were estimated to be − 2.0 ± 0.5 PgC year−1 and − 0.3 (PgC year−1) decade−1, respectively. Our analysis revealed that oceanic CO2 uptake decreased during the 1990s and has been increasing since 2000. Our estimate of the globally averaged rate of pH change, − 0.0181 ± 0.0001 decade−1, was consistent with that expected from the trend of atmospheric CO2 growth. However, rates of decline of pH were relatively slow in the Southern Ocean (− 0.0165 ± 0.0001·decade−1) and in the western equatorial Pacific (− 0.0148 ± 0.0002·decade−1). Our estimate of the globally averaged rate of pH change can be used to verify Indicator 14.3.1 of Sustainable Development Goals.

Application of mild pulsed electric fields on starter culture accelerates yogurt fermentation

The goal of this work was to investigate the influence of pulsed electric fields (PEF) operational parameters on a mixture of Streptococcus thermophilus DIL 5218 and Lactobacillus delbrueckii subsp. bulgaricus DSMZ 20081T with regards to the culture’s acidification capability in reconstituted skim milk medium. We investigated the effects of field strength, pulse frequency and total number of pulses by use of design of experiments and a two-level full factorial design. The responses were the cell counts of the two microorganisms after PEF application, the pH lag phase λpH, the maximum pH change rate µmax, the maximum pH change and the oxidation/reduction potential (ORP). The application of PEF on the mixed culture accelerated the acidification of milk by an average of 12 min in an approx. 160 min lasting control λpH. In contrast the maximum pH change rate µmax and the maximum pH change decreased slightly in fermentations with PEF-treated cultures. Furthermore, a significantly faster decrease of the oxidation/reduction potential (ORP) already within the first 30 min and a lower final ORP was observed in milk fermented with PEF-treated culture. The total number of pulses applied was the most influencing factor in most of the responses measured. We hypothesized that the reason for the enhanced performance of the PEF-treated culture was a combination of an oxidative stress response of S. thermophilus DIL 5218 and an enhanced proteolytic phenotype in L. delbrueckii subsp. bulgaricus DSMZ 20081T.

Application of guar gum-based edible coatings supplemented with spice extracts to extend post-harvest shelf life of lemon (Citrus limon)

Guar gum based edible coatings supplemented with condiments’ extracts (methanolic and ethanolic extract of fennel, bay leaf, coriander and nigella seeds) were assayed for lemon for the maintenance of parameters that determine the quality during postharvest life. Rate of change in pH, titratable acidity and total soluble solids were studied during the shelf life of lemons. Results obtained from all the assays were communicated as mean ± standard deviation. One-way analysis of variance and t-test was employed on the studied factors at P≤0.05 to study the effect of guar gum containing extracts. The shelf life of ethanolic and methanolic extract of fennel coated lemons was significantly increased up to 24 weeks at 10 °C (85% relative humidity) while all other treatments had 15 weeks of storage stability. Treated lemons showed less changes in physicochemical attributes than both controls (untreated control; UN and treated control; GG). In addition to biochemical parameters, the storage parameters of lemon, such as antioxidant content, ascorbic acid, total phenolic content, carotenoid and chlorophyll pigments and total flavonoid content were significantly delayed in treated lemons as compared to controls. Bacterial load was also reduced in treated lemons. Coatings based on guar gum fortified with extracts could be an effective tool to delay ripening process and maintain quality of lemons during cold storage. As the constituents of these coatings are derived from food grade products, these coatings are therefore safe for human consumption and eco-friendly. These coatings not only protect the lemon from the contaminating microbes but also have bactericidal effects on the bacteria that were already present inside the lemon. Moreover, the active component of these coatings, i.e. extracts are derived from culinary spices that are easily available throughout the year.

Redistribution characteristics of atmospheric precipitation in different spatial levels of Guangzhou urban typical forests in southern China

The aims of the present study were to determine the pH variation and chemical feature of atmospheric precipitation during the research period. We also investigated the redistribution characteristics of rainfall while passing through the canopy layer, leaf-litter layer and soil layer, successively to quantify the acid rain buffering capacity of these spatial levels in the evergreen broadleaved forest (EBF), deciduous broadleaved forest (DBF) and coniferous forest (CF) in Guangzhou urban area, China. Results showed that the rainfall was typically acidic, and the acid rain type in Guangzhou urban area is converted from sulfuric acid type to mixed type of sulfuric acid and nitric acid. The major ions from the canopy to the forest floor differed within the three forest types. However, the enrichment phenomenon of base cations in soil leachate in EBF and DBF implied that nutrient loss was more serious in the broadleaved forest than in the coniferous forest. Variability of ionic concentration and pH in the vertical sequence of different tree species showed that the net ion concentration variation index has a significant conic relationship with ne pH change rate. We also built an acid rain buffering index, which combines the neutralization and interception effects of vegetation to acid rainfall. The present results indicated that the three forest types in urban Guangzhou all have certain buffering capacity to acid rain, and following the order: DBF > EBF > CF. In the meanwhile, the forest canopy is the biggest acid rain buffer in urban Guangzhou, following by the soil.

Early pH change predicts intensive care unit mortality

Aim of the Study:Metabolic acidosis is associated with increased mortality in critically ill patients. We hypothesized that early correction of acidosis of presumed metabolic origin results in improved outcomes.Patients and Methods:We conducted a prospective, observational study from February 2015 to June 2016 in a 12 bed mixed intensive care unit (ICU) of a 1000 bed tertiary care hospital in the north of India. ICU patients aged above 18 years with an admission pH ≥7.0 to <7.35 of presumed metabolic origin were included. Arterial blood gas parameters including pH, PaO2, PaCO2, HCO3−, Na+, K+, Cl−, anion gap (AG), base excess, and lactate at 0, 6, and 24 h along with other standard laboratory investigations were recorded. The primary outcome was to assess the impact of early pH changes on mortality at day 28 of ICU.Results:A total of 104 patients with 60.6% males and 91.3% medical patients were included in the study. Sepsis of lung origin (60.6%) was the predominant etiology. By day 28, 68 (65.4%) patients had died. Median age was 49.5 years, weight 61.7 kg, Sequential Organ Failure Assessment, and Acute Physiologic and Chronic Health Evaluation II scores were 16 and 12, respectively. Nonsurvivors had a higher vasopressor index (P < 0.01), lactate and central venous oxygen saturation (P < 0.05), and lower pH (P < 0.05). A pH correction/change of ≥1.16% during the first 24 h had the best receiver operating characteristic for predicting survival at day 28, with area under the curve (95% confidence interval, 0.72 [0.62–0.82], P < 0.05) compared to HCO3-, BE, lactate, and AG.Conclusions:Metabolic acidosis is associated with higher mortality in ICU. The rate of change in pH may better predict ICU mortality than other metabolic indices.

Impact of medium pH regulation on biohydrogen production in dark fermentation process using suspended and immobilized microbial cells

ABSTRACTThe effect of pH regulation on biohydrogen production was studied using suspended and immobilized mixed cultures. Four sets of dark fermentation processes were carried out using suspended cells under regulated pH (Sus_R) and non-regulated pH conditions (Sus_N), the nalginate-immobilized cells under pH regulated (Imm_R) and non-pH regulated conditions (Imm_N). Sus_R showed a peak hydrogen fraction of 44% and complete glucose degradation, compared to Sus_N with a peak hydrogen fraction of 36% and a glucose degradation of 37%. Imm_R experiments showed a peak biohydrogen fraction of 35%, while the peak hydrogen fraction observed with Imm_N was 22%.The highest hydrogen fraction was observed using Sus_R conditions. A 100% glucose degradation was observed in both pH regulated and non-regulated processes using immobilized cells. The rate of pH change was slower for immobilized cells compared to suspended cells suggesting a better buffering capacity under non-pH regulated conditions. The study showed that biohydrogen production with suspended cells in a non-regulated pH environment resulted in early termination of the process and lower productivity.

An Insightful Theoretical Interpretation of Paper pH Surface Electrode Data Reveals a New Paradigm for the Definition of Paper Acidity

Electrochemical measurement of pH on paper artifacts is a very important tool to assess the state of paper conservation. Different methods using different types of electrodes have been standardized to provide reproducible pH values of paper. One of these methodologies is not very invasive since it is made on the paper surface by means of a surface electrode in contact with the paper through a small layer of water previously added at the measurement point. This method is very convenient but suffers from the fact that the pH value given by the instrument is continuously changing during the measurement with a very fast rate in the first seconds and tending to reach a plateau value after very long time. Usually, the measure is taken at a time after which the rate of pH change is below a given value, i.e., when the value can be considered constant. This condition is usually signaled by an automatic instrumental alert provided to the operator. This pH value, however, is not the asymptotic one, which can be reac...

Deducing acidification rates based on short-term time series.

We show that, statistically, the simple linear regression (SLR)-determined rate of temporal change in seawater pH (βpH), the so-called acidification rate, can be expressed as a linear combination of a constant (the estimated rate of temporal change in pH) and SLR-determined rates of temporal changes in other variables (deviation largely due to various sampling distributions), despite complications due to different observation durations and temporal sampling distributions. Observations show that five time series data sets worldwide, with observation times from 9 to 23 years, have yielded βpH values that vary from 1.61 × 10−3 to −2.5 × 10−3 pH unit yr−1. After correcting for the deviation, these data now all yield an acidification rate similar to what is expected under the air-sea CO2 equilibrium (−1.6 × 10−3 ~ −1.8 × 10−3 pH unit yr−1). Although long-term time series stations may have evenly distributed datasets, shorter time series may suffer large errors which are correctable by this method.

Growth Behavior of Monohydrocalcite (CaCO3·H2O) in Silica-Rich Alkaline Solution

Monohydrocalcite (CaCO3·H2O) has been crystallized in silica-rich alkaline water solution. The crystallization proceeds by a counterdiffusion method without the presence of any other additive except dissolved silica. The crystallization has been followed in situ by optical microscopy and Raman microspectroscopy, while the time evolution of the pH and the concentration of calcium and silica species in solution have also been followed either by in situ (pH) or ex-situ (calcium and silica) time-lapse analysis. The growth of monohydrocalcite particles occurs by different mechanisms that are related to the pH and the rate of pH change with time. The initial peanut-like crystal converts into an onion-like multilayered texture, which is built up by the alternation of loose layers and compact layers as a result of different levels of silica incorporation. A final silica-rich skin covers the hemisphere inhibiting the further growth of monohydrocalcite. When the silica skin fails to cover the whole surface of the hemisphere, a bulge of monohydrocalcite grows from the uncovered area until a new silica skin inhibits its growth except from a small uncovered area from which a new bulge forms. The iteration of this mechanism creates particles with caterpillar-like morphology. Our results show that silica plays a key role in the morphogenesis and texture of monohydrocalcite crystallization due to the coupled interaction between the reverse solubility of silica and carbonate versus pH.

Using the hydrolysis of anhydrides to control gel properties and homogeneity in pH-triggered gelation

The rate of pH change does not affect the primary assembly of a gelator, but does control the mechanical properties of the gel.

Tuning the mechanical and morphological properties of self-assembled peptide hydrogels via control over the gelation mechanism through regulation of ionic strength and the rate of pH change

Hydrogels formed by the self-assembly of peptides are promising biomaterials. Here we demonstrate that the final material properties of a bioactive self assembled peptide system can be determined via control over the assembly conditions.

Resultados inesperados de medición directa, con una microbalanza de torsión en un sistema cerrado, de las tasas de calcificación de los corales Agaricia agaricites (Scleractinia:Agariicidae) y concomitantes cambios de pH en el medio del mar

Ocean acidification is impacting the calcification of corals, but the mechanisms of calcification are still unclear. To explore the relationship between calcification and pH, small pieces of coral were suspended from a torsion microbalance in gently stirred, temperature controlled, seawater in a closed chamber. Net calcification rate and pH were continuously monitored while light, temperature or pH could be manipulated. The coral pieces were from the edges of thin plates of Agaricia agaricites and were studied alive and freshly collected. Unexpectedly, when calcification was taking place (n=9, 0.082 mg.hr-1.cm-2), as determined by weight increase, the pH of the surrounding seawater medium changed little (n=10, -0.0047 pH units.hr-1.cm-2). When calcification was not taking place the decrease of seawater pH was an order of magnitude higher, -0.013 pH units.hr-1.cm-2. This is the opposite of what is expected when calcium carbonate (CaCO3) forms. Similarly, fresh skeleton initially showed no change of pH in the seawater medium although the rates of weight gain were high (upto 1.0 mg hr-1.cm-2). After 10 hours, as the rate of deposition decreased following a generalized Michaelis-Menten growth curve, the pH began to decrease dramatically indicating an increase of CO2 in the seawater. These unexpected results can be explained if unstable calcium bicarbonate (Ca(HCO3)2) is formed in the organic matrix/carbonic anhydrase surface and slowly transforms later to CaCO3. Pieces of living coral monitored in the chamber for 30 hours gained weight during the day and loss it at night. The loss would be consistent with the transformation of Ca(HCO3)2 to CaCO3 with the release of CO2. The mean calcification rate of live coral was greater (n=8, p=0.0027) in high light (120 μmol.s-1.m-2) at 0.098 mg.hr-1.cm-2, compared to 0.063 mg.hr-1.cm-2 in low light (12 μmol.s-1.m-2). However, at the same time the mean rate of pH change was -0.0076 under low light compared to -0.0030 under high light (n=8, p=0.0001). The difference can be explained by CO2 being used for photosynthesis by zooxanthellae. The deposition rate of live coral was not affected by the addition of phosphate but the rate of weight gain by the freshly collected skeleton was strongly enhanced by phosphate. These results indicate that care should be applied in the application of the alkalinity anomaly technique for the measurement of calcification in corals. Rev. Biol. Trop. 62 (Suppl. 3): 25-38. Epub 2014 September 01.