A New Planar Potentiometric Sensor for In Situ Measurements.

A new construction of a potentiometric sensor was introduced for the first time. It relies on the use of two membranes instead of one, as in the well-known coated-disc electrode. For this purpose, a new electrode body was constructed, including not one, but two glassy carbon discs covered with an ion-selective membrane. This solution allows for the sensor properties to be enhanced without using additional materials (layers or additives) on the membrane. The new construction is particularly useful for in situ measurements in environmental samples. Two ion-selective polymeric membranes were used, namely H+ and K+-selective membranes, to confirm the universality of the idea. The tests conducted included chronopotentiometric tests, electrochemical impedance spectroscopy, and potentiometric measurements. The electrical and analytical parameters of the sensors were evaluated and compared for all tested electrodes to evaluate the properties of the planar electrode versus previously known constructions. Research has shown that the application of two membranes instead of one allows for the resistance of an electrode to be lowered and for the electrical capacitance to be elevated. Improving the electrical properties of an electrode resulted in the enhancement of its analytical properties. The pH measurement range of the planar electrode is 2-11, which is much wider in contrast to that of the single-membrane electrode. The linear range of the K+-selective planar electrode is wider than that of the coated-disc electrode and equals 10-6 to 10-1 M. The response time turned out to be a few seconds shorter, and the potential drift was smaller due to the application of an additional membrane in the electrode construction. This research creates a new opportunity to design robust potentiometric sensors, as the presented construction is universal and can be used to obtain electrodes selective to various ions.

Positively Charged Organosilanes Covalently Linked to the Silica Network as Modulating Tools for the Salinity Correction of pH Values Obtained with Colorimetric Sensor Arrays (CSAs).

Seven increasing levels of water salinity from 0.029 to 0.600 M (as NaCl) were used to investigate the dependence of pH measurement, performed using colorimetric sensor arrays (CSAs), on ionic strength. The CSAs were arrays of sensing spots prepared in the form of sol-gel-embedding Bromothymol Blue (BB) and Bromocresol Green (BCG) in a porous nitrocellulose support. The support was impregnated over the entire thickness (≈100 µm), allowing for the signal (Hue) acquisition on the opposite side to the contact with the sample solution. Three CSAs were prepared, M1, M2, and M3. M1 contained a free cationic surfactant, hexadecyltrimethylammonium p-toluenesulfonate (CTApTs), for modulating the pKa of the indicators. In M2, the surfactant dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DTSACl) was covalently bonded to the sol-gel. M3 was prepared like M2 but using a larger amount of ethanol as the solvent for the synthesis. The modulation of the CTApTs or the DTSACl concentration enabled the tuning of the pKa. In general, the pKa modulation ability decreased with the increase in salinity. The presence of a surfactant covalently linked to the backbone partially reduced the competitiveness of the anionic species, improving the results. Nevertheless, the salt effect was still present, and a correction algorithm was required. Between pH 5.00 and 12.00, this correction could be made automatically by using spots taken as references to produce sensors independent of salinity. As the salt effect is virtually absent above 0.160 M, M2 and M3 can be used for future applications in seawater.

Anodic H2O2 Generation in Carbonate-Based Electrolytes-Mechanistic Insight from Scanning Electrochemical Microscopy.

For the anodic H2O2 generation, it has been shown that the electrolyte composition can steer the reaction pathway toward increased H2O2 generation. Previous efforts made on composition optimization found that the impact of the molar fraction of carbonate species varies for different anodes, and therefore, controversies remain concerning the reaction pathways as well as the species involved in H2O2 formation. Considering that water oxidation results in the liberation of protons within the anode microenvironment, the corresponding acidification would cause an equilibrium shift between carbonate species, which in turn may modulate the reaction pathway. We determined the changes in the fraction of carbonate species in the vicinity of an anode by performing local pH measurements using a Au nanoelectrode positioned in close proximity to an operating anode by shear-force scanning electrochemical microscopy (SECM). It could be confirmed that the main anionic species at the interface is HCO3 -, at potentials where H2O2 is preferentially formed, regardless of the pH value in the bulk. The simultaneous use of a Au-Pt double barrel microelectrode in generator-collector SECM measurements demonstrates that the local HCO3 - concentration is collectively determined by the oxidation current, buffer capacity, and bulk pH of the electrolyte.

Detecting pH of Sub-Micrometer Aerosol Particles Using Fluorescent Probes.

Acidity is one of the most fundamental properties of atmospheric aerosol particles, influencing both chemical processes and environmental impacts. A couple of methods for measuring the pH of aerosol particles have been developed, yet no approach is currently available for quantifying the pH of suspending submicron particles. We developed an aerosol fluorescence cell (AFC) for quantifying the pH of aerosol particles in a continuous flow. Particles containing fluorescent pH probes (fluorescein and Oregon green 488) were injected into the AFC. Ratiometric analysis of pH for these particles was conducted by alternatively exciting them with two wavelengths of diode lasers (450 and 488 nm). The employment of the two types of fluorescent probes allowed the measurement of pH in the range of 2-7. The pH measurement by the AFC for submicron particles was compared with that measured by using pH indicator papers, providing a reasonably good agreement. Measurement of size-selected particles suggested that the AFC approach is applicable to particles of 80 nm in diameter. In combination with recent developments for analyzing renebulized water-soluble matter samples, we suggest that the AFC method can be applied not only for laboratory standards but also for atmospherically relevant samples in the future.

Ratiometric fluorescent probe based on non-conjugated polymer dots for pH measurements in ordinary Portland cement-based materials.

An organic fluorescent probe, citric acid-1,3-Propanediamine-Rhodamine B (CPR) was synthesized to determine pH of ordinary Portland cement requiring only a small sample size (less than 500 µL cement leachate). The SEM, XRD, and FTIR investigations demonstrate that citric acid-1,3-Propanediamine are polymer dots with a fusiform structure. Ratio pH probe is constructed by rhodamine B with polymer dots, which exhibits a linear response in high alkaline range. A 6-fold increase in fluorescence intensity (455 nm) is achieved at pH from 12.00 to 13.25. Combined with measurements of the isothermal calorimeter, mineral composition, and microscopic morphology, variation of pH is used to evaluate the changes of components during hydration. Furthermore, CPR can be applied to measure pH of high-dose pulverized fuel ash blending systems, the non-pure cement with slightly lower alkalinity.

Measurement of intraluminal pH changes in the gastrointestinal tract of mice with gastrointestinal diseases.

As a fundamental and essential property, gastrointestinal (GI) tract pH reflects its condition and changes in several GI diseases such as inflammatory bowel disease (IBD), gastritis, etc. As a result, accurately measuring the GI pH is crucial for treatment, diagnosis, and prevention of GI diseases and contributes to developing GI disease models for basic studies. However, among pH measuring studies with animal models, there is no reliable method that can reflect the value and changing trends of GI pH in actual patients. In the current study, we developed a fast, simple method with pH indicator paper to measure the GI pH changes with GI content in normal mice and mice with colitis or hepatitis. Results demonstrated that normal mice's mean GI pH values were between 6.0 and 8.0, which was consistent with previous reports. Furthermore, the GI pH of colitis and hepatitis model mice showed the same pattern of lower values in the intestine and higher values in the stomach compared with normal mice. Our simple and timesaving method can accurately measure the dramatic changes in the GI pH of mice with GI diseases and is suitable for measuring the pH of sticky liquids with limited volume. Given all the merits listed above, this method is helpful for further research.

Non-Destructive Measurement of Acetic Acid and Its Distribution in a Photovoltaic Module during Damp Heat Testing Using pH-Sensitive Fluorescent Dye Sensors.

An optical pH sensor that enables the non-destructive measurement of acetic acid and its distribution in a photovoltaic module during damp heat (DH) testing is reported. The sensor was fabricated by impregnating a solution of a pH-sensitive fluorescent dye into a fluororesin membrane filter, which was then dried. While conducting the DH test, fluorescence spectra from 20 pH sensors were periodically recorded and converted into pH values using a predetermined calibration curve. As a result, we succeeded in measuring changes in pH with a DH test time of up to 2000 h, and it was possible to obtain information on the pH distribution in the module. We also confirmed no change in pH in a module with a silicone encapsulant free from acetic acid, and revealed that the sensor that we developed does not respond to moisture and heat, but only to acetic acid.

Measuring Protons with Photons: A Hand-Held, Spectrophotometric pH Analyzer for Ocean Acidification Research, Community Science and Education.

Ocean Acidification (OA) is negatively affecting the physiological processes of marine organisms, altering biogeochemical cycles, and changing chemical equilibria throughout the world's oceans. It is difficult to measure pH broadly, in large part because accurate pH measurement technology is expensive, bulky, and requires technical training. Here, we present the development and evaluation of a hand-held, affordable, field-durable, and easy-to-use pH instrument, named the pHyter, which is controlled through a smartphone app. We determine the accuracy of pH measurements using the pHyter by comparison with benchtop spectrophotometric seawater pH measurements, measurement of a certified pH standard, and comparison with a proven in situ instrument, the iSAMI-pH. These results show a pHyter pH measurement accuracy of ±0.046 pH or better, which is on par with interlaboratory seawater pH measurement comparison experiments. We also demonstrate the pHyter's ability to conduct both temporal and spatial studies of coastal ecosystems by presenting data from a coral reef and a bay, in which the pHyter was used from a kayak. These studies showcase the instrument's portability, applicability, and potential to be used for community science, STEM education, and outreach, with the goal of empowering people around the world to measure pH in their own backyards.

Regression Analysis of Orthogonal, Cylindrical and Multivariable Color Parameters for Colorimetric Surface pH Measurement of Materials.

The surface pH is a critical factor in the quality and longevity of materials and products. Traditional fast colorimetric pH detection-based tests such as water quality control or pregnancy tests, when results are determined by the naked eye, cannot provide quantitative values. Using standard pH papers, paper-printed comparison charts, or colorimetric microfluidic paper-based analytical devices is not suitable for such technological applications and quality management systems (QMSs) where the particular tested material should contain a suitable indicator in situ, in its structure, either before or after the process, the technology or the apparatus that are being tested. This paper describes a method based on the combination of impregnation of a tested material with a pH indicator in situ, its exposure to a process of technology whose impact on pH value is to be tested, colorimetric pH measurement, and approximation of pH value using derived pH characteristic parameters (pH-CPs) based on CIE orthogonal and cylindrical color variables. The hypotheses were experimentally verified using the methyl red pH indicator, impregnating the acid lignin-containing paper, and preparing a calibration sample set with pH in the range 4 to 12 using controlled alkalization. Based on the performed measurements and statistical evaluation, it can be concluded that the best pH-CPs with the highest regression parameters for pH are √∆E, ln (a),√∆H (ab), a/L, h/b and ln (b/a). The experimental results show that the presented method allows a good estimation of pH detection of the material surfaces.

Purified meta-Cresol Purple dye perturbation: How it influences spectrophotometric pH measurements.

Ocean acidification, a phenomenon of seawater pH decrease due to increasing atmospheric CO2, has a global effect on seawater chemistry, marine biology, and ecosystems. Ocean acidification is a gradual and global long-term process, the study of which demands high-quality pH data. The spectrophotometric technique is capable of generating accurate and precise pH measurements but requires adding an indicator dye that perturbs the sample original pH. While the perturbation is modest in well-buffered seawater, applications of the method in environments with lower buffer capacity such as riverine, estuarine, sea-ice meltwater and lacustrine environments are increasingly common, and uncertainties related to larger potential dye perturbations need further evaluation. In this paper, we assess the effect of purified meta-Cresol Purple (mCP) dye addition on the sample pH and how to correct for this dye perturbation. We conducted numerical simulations by incorporating mCP speciation into the MATLAB CO2SYS program to examine the changes in water sample pH caused by the dye addition and to reveal the dye perturbation mechanisms. Then, laboratory experiments were carried out to verify the simulation results. The simulations suggest that the dye perturbation on sample pH is a result of total alkalinity (TA) contributions from the indicator dye and chemical equilibrium shifts that are related to both the water sample properties (pH, TA, and salinity) and the indicator dye solution properties (pH and solvent matrix). The laboratory experiments supported the simulation results; the same dye solution can lead to different dye perturbations in water samples with different pH, TA, and salinity values. The modeled adjustments agreed well with the empirically determined adjustments for salinities > 5, but it showed greater errors for lower salinities with disagreements as large as 0.005 pH units. Adjustments are minimized when the pH and salinity of the dye are matched to the sample. When the dye is used over a wide range of salinity, we suggest that it should be prepared in deionized water to minimize the dye perturbation effect on pH in the fresher sample waters with less well-constrained perturbation adjustments. We also suggest that the dye perturbation correction should be based on double dye addition experiments performed over a wide range of pH, TA, and salinity. Otherwise, multiple volume dye addition experiments are recommended for each sample to determine the dye perturbation adjustment. We further create a MATLAB function dyeperturbation.m that calculates the expected dye perturbation. This function can be used to validate empirically-derived adjustments or in lieu of empirical adjustments if dye addition experiments are unfeasible (e.g., for historical data). This study of dye perturbation evaluation and correction will improve the accuracy of the pH data, necessary for monitoring the long-term anthropogenic-driven changes in the seawater carbonate system.

Cross-linkage urease nanoparticles: a high-efficiency signal-generation tag for portable pH meter-based electrochemical immunoassay of lipocalin-2 protein diagnostics.

An innovative signal-transduction tag based on cross-linked urease nanoparticles (CLENP) was designed for the development of a pH meter-based immunoassay of lipocalin-2 (LCN2). The CLENP was synthesized with a typical desolvation method using ethanol as desolvation agent, followed by functionalization with polyaspartic acid. The carboxylated CLENP were used as the signal-generation tags for the labelling of secondary antibodies via the carbodiimide coupling. Upon target LCN2 introduction, a sandwich-type immune reaction was performed between capture antibody-coated plate and the labeled secondary antibody on the CLENP. The conjugated CLENP in the microplate hydrolyzed urea into ammonia (NH4+) and carbonate (CO32-), resulting in the pH change of solution, which was determined with a handheld pH meter. The pH variation was proportional to target concentration in the sample. By monitoring the pH variation of the urea solution, the level of LCN2 at a concentration as low as 5.2 pg mL-1 was evaluated. The pH meter-based electrochemical immunoassay can be utilized for mass production of miniaturized lab-on-a-chip devices with handheld pH meter, thereby opening new opportunities for protein diagnostics and biosecurity. Graphical abstract An innovative signal-transduction tag based on cross-linked urease nanoparticles was designed for high-efficiency immunoassay of lipocalin-2 with pH meter readout.

Uso de una matriz autóloga en el tratamiento de úlceras de pie diabético, con espectroscopia de infrarrojo cercano y medidor de pH dérmico.

OBJECTIVE: Evaluate the efficiency of an autologous whole blood clot (WBC) matrix on diabetic foot ulcers (DFU), and analyse its immune response with near-infrared spectroscopy (NIRS) and pH measurement. METHOD: Three patients were treated with a WBC. The matrix was produced at the point of care, using a WBC system. A WBC gel was formed and applied onto the wounds. The gel remained in place with primary and secondary dressings. RESULTS: Wound-size reduction was 70% after two applications, 97.6% after three applications, and 90.9% after four applications. The NIRS skeletal muscle oxygen saturation (StO2) increased in all cases. CONCLUSION: The autologous matrix was efficient in treating DFU. The wound area surface reduced after each application and wound healing was achieved in all cases. More studies are needed to understand the benefits of using a WBC matrix on DFU.

OBJETIVO: Evaluar la eficacia de una matriz autóloga en el tratamiento de úlceras de pie diabético (UPD) de difícil cicatrización, y analizar la respuesta inmune a la aplicación de la matriz con un escáner de infrarrojo cercano (NIRS, por sus siglas en inglés) y un medidor de pH dérmico. MÉTODO: Tres pacientes fueron tratados con una matriz de coágulo de sangre completa (WBC, por sus siglas en inglés) autóloga. La matriz se realizó en el punto de atención, mezclando la sangre del paciente con una suspensión coloidal de gluconato de calcio/caolín, e inyectándola en una bandeja de coagulación. Se formó un gel de WBC y se aplicó a las heridas. El gel de WBC se mantuvo en su lugar con apósitos primarios y secundarios. RESULTADOS: Hubo una reducción del tamaño de las UPD de 70% tras dos aplicaciones, 97,6% después de tres aplicaciones, y 90,9% tras cuatro aplicaciones. El NIRS midió un aumento en la saturación de oxígeno tisular. No hubo reacciones adversas. CONCLUSIÓN: La matriz autóloga fue eficaz en el tratamiento de las UPD. La superficie de las UPD se redujo después de cada aplicación y se logró el cierre completo de las heridas. Se necesitan más ensayos clínicos para comprender mejor los beneficios de la matriz de WBC en UPD. CONFLICTO DE INTERÉS: RedDress Ltd. (Pardes-Hanna, Israel) proporcionó los suministros y materiales del estudio. Bennett Health Inc. ayudó con el desarrollo del protocolo y capacitó al personal sobre la aplicación del producto para coágulos sanguíneos. JA es accionista de Bennett Health Inc. No hubo interés financiero para ninguno de los investigadores o participantes.

pH Colorimetric Sensor Arrays: Role of the Color Space Adopted for the Calculation of the Prediction Error.

A pH colorimetric sensor array was prepared and characterized by combining tetrabromophenol blue (TBB) and bromothymol blue (BB) embedded in organically modified silicate (OrMoSil) spots polyvinylidene fluoride (PVDF)-supported. The signal was based on the Hue profile (H). The individual calibrations of TBB and BB showed precisions with minimum values of 0.012 pH units at pH = 2.196 for TBB and 0.018 at pH = 6.692 for BB. The overall precision of 10 spots of the mixture TBB/BB increased in the pH range of 1.000-8.000 from a minimum value of pH precision of 0.009 at pH = 2.196 to 0.012 at pH = 6.692, with the worst value of 0.279 pH units at pH = 4.101. The possibility to produce an array with much more than 10 spots allows for improving precision. The H analytical performance was compared to those of other color spaces such as RGB, Lab, and XYZ. H was the best one, with prediction error in the range of 0.016 to 0.021 pH units, at least three times lower than the second-best (x coordinate), with 0.064 pH units. These results were also confirmed by the calculation of the main experimental contributions to the pH prediction error, demonstrating the consistency of the proposed calculation approach.

Direct Evidence of Local pH Change and the Role of Alkali Cation during CO2 Electroreduction in Aqueous Media.

We report, for the first time, utilizing a rotating ring-disc electrode (RRDE) assembly for detecting changes in the local pH during aqueous CO2 reduction reaction (CO2 RR). Using Au as a model catalyst where CO is the only product, we show that the CO oxidation peak shifts by -86±2 mV/pH during CO2 RR, which can be used to directly quantify the change in the local pH near the catalyst surface during electrolysis. We then applied this methodology to investigate the role of cations in affecting the local pH during CO2 RR and find that during CO2 RR to CO on Au in an MHCO3 buffer (where M is an alkali metal), the experimentally measured local basicity decreased in the order Li+ > Na+ > K+ > Cs+ , which agreed with an earlier theoretical prediction by Singh et al. Our results also reveal that the formation of CO is independent of the cation. In summary, RRDE is a versatile tool for detecting local pH change over a diverse range of CO2 RR catalysts. Additionally, using the product itself (i.e. CO) as the local pH probe allows us to investigate CO2 RR without the interference of additional probe molecules introduced to the system. Most importantly, considering that most CO2 RR products have pH-dependent oxidation, RRDE can be a powerful tool for determining the local pH and correlating the local pH to reaction selectivity.

Establishment of a novel and effective reflux laryngitis model in rabbits: a preliminary study.

PURPOSE: To establish a novel and effective reflux model with a modified nasogastric aspiration tube and to investigate the association between different types of nasogastric aspiration tubes and reflux laryngitis, we conducted this study. METHODS: Thirty-eight healthy New Zealand albino rabbits (2.5-3.5 kg) were divided into three groups: control (CTR, n = 6)-non-intubated; normal nasogastric intubation (NNI, n = 16)-intubated with 4#, 6#, 8#, and 10# normal nasogastric aspiration tubes; and modified nasogastric intubation (MNI, n = 16)-intubated with 4#, 6#, 8#, and 10# modified nasogastric aspiration tubes. The laryngoscopy, body weight, and pH values at the esophageal entrance were recorded before and 1, 2, and 4 weeks after intubation. After the final laryngoscopy, the animals in groups with a pH below 4 were sacrificed to obtain histological and gene expression analysis results. RESULTS: The reflux finding score (RFS) after 4 weeks showed that there was a statistically significant difference in the 8# NNI group (7 ± 0.816, P < 0.001), the 8# MNI group (11.5 ± 2.517, P < 0.001) and the 10# MNI (12.75 ± 1.893, P < 0.001) group compared with the control group (1.83 ± 1.602). The pH values of these three groups were lower than 4. However, the weight loss of the rabbits in the 10# NNI and 10# MNI groups was more obvious. Submucous gland hyperplasia and inflammation were significantly increased in the 8# NNI group, 8# MNI group and the 10# MNI group, but in the level of some pro-inflammatory cytokines and COX-2, the MNI group was significantly higher than the NNI group (8# NNI × 8# MNI, P < 0.01; 8# MNI × 10# MNI, P < 0.01). CONCLUSION: This study showed that 8# modified nasogastric intubation (MNI) produces effective reflux laryngitis in the rabbits.

Measurement of Internal pH in Helicobacter pylori by Using Green Fluorescent Protein Fluorimetry.

Helicobacter pylori is an organism known to colonize the normal human stomach. Previous studies have shown that the bacterium does this by elevating its periplasmic pH via the hydrolysis of urea. However, the value of the periplasmic pH was calculated indirectly from the proton motive force equation. To measure the periplasmic pH directly in H. pylori, we fused enhanced green fluorescent protein (EGFP) to the predicted twin-arginine signal peptides of HydA and KapA from H. pylori and TorA from Escherichia coli The fusion proteins were expressed in the H. pylori genome under the control of the cagA promoter. Confocal microscopic and cell fractionation/immunoblotting analyses detected TorA-EGFP in the periplasm and KapA-EGFP in both the periplasm and cytoplasm, while the mature form of HydA-EGFP was seen at low levels in the periplasm, with major cytoplasmic retention of the precursor form. With H. pylori expressing TorA-EGFP, we established a system to directly measure periplasmic pH based on the pH-sensitive fluorimetry of EGFP. These measurements demonstrated that the addition of 5 mM urea has little effect on the periplasmic pH at a medium pH higher than pH 6.5 but rapidly increases the periplasmic pH to pH 6.1 at an acidic medium pH (pH 5.0), corresponding to the opening of the proton-gated channel, UreI, and confirming the basis of gastric colonization. Measurements of the periplasmic pH in an HP0244 (FlgS)-deficient mutant of H. pylori expressing TorA-EGFP revealed a significant loss of the urea-dependent increase in the periplasmic pH at an acidic medium pH, providing additional evidence that FlgS is responsible for recruitment of urease to the inner membrane in association with UreI.IMPORTANCEHelicobacter pylori has been identified as the major cause of chronic superficial gastritis and peptic ulcer disease. In addition, persistent infection with H. pylori, which, if untreated, lasts for the lifetime of an infected individual, predisposes one to gastric malignancies, such as adenocarcinoma and mucosa-associated lymphoid tissue (MALT) lymphoma. A unique feature of the neutralophilic bacterium H. pylori is its ability to survive in the extremely acidic environment of the stomach through its acid acclimation mechanism. The presented results on measurements of periplasmic pH in H. pylori based on fluorimetry of fully active green fluorescent protein fusion proteins exported with the twin-arginine translocase system provide a reliable and rapid tool for the investigation of acid acclimation in H. pylori.

Measuring magnetosomal pH of the magnetotactic bacterium Magnetospirillum magneticum AMB-1 using pH-sensitive fluorescent proteins.

Magnetotactic bacteria synthesize uniform-sized and regularly shaped magnetic nanoparticles in their organelles termed magnetosomes. Homeostasis of the magnetosome lumen must be maintained for its role accomplishment. Here, we developed a method to estimate the pH of a single living cell of the magnetotactic bacterium Magnetospirillum magneticum AMB-1 using a pH-sensitive fluorescent protein E2GFP. Using the pH measurement, we estimated that the cytoplasmic pH was approximately 7.6 and periplasmic pH was approximately 7.2. Moreover, we estimated pH in the magnetosome lumen and cytoplasmic surface using fusion proteins of E2GFP and magnetosome-associated proteins. The pH in the magnetosome lumen increased during the exponential growth phase when magnetotactic bacteria actively synthesize magnetite crystals, whereas pH at the magnetosome surface was not affected by the growth stage. This live-cell pH measurement method will help for understanding magnetosome pH homeostasis to reveal molecular mechanisms of magnetite biomineralization in the bacterial organelle.

LED-CT Scan for pH Distribution on a Cross-Section of Cell Culture Medium.

In cell culture, the pH of the culture medium is one of the most important conditions. However, the culture medium may have non-uniform pH distribution due to activities of cells and changes in the environment. Although it is possible to measure the pH distribution with an existing pH meter using distributed electrodes, the method involves direct contact with the medium and would greatly increase the risk of contamination. Here in this paper, we propose a computed tomography (CT) scan for measuring pH distribution using the color change of phenol red with a light-emitting diode (LED) light source. Using the principle of CT scan, we can measure pH distribution without contacting culture medium, and thus, decrease the risk of contamination. We have developed the device with a LED, an array of photo receivers and a rotation mechanism. The system is firstly calibrated with different shapes of wooden objects that do not pass light, we succeeded in obtaining their 3D topographies. The system was also used for measuring a culture medium with two different pH values, it was possible to obtain a pH distribution that clearly shows the boundary.

Over One-Year Long-Term Laboratory Tests of pH Electrodes in Terms of Industrial Applications Checking Stabilities of Their Parameters and Their Influence on Uncertainties of Measurements.

Glass pH electrodes are still successfully applied in the chemical and environmental industry. During their long-term use, periodic calibration is required to maintain the required accuracy of measurements because the parameters of the electrodes change over time. This work presents an aging of 11 pH electrodes within approximately 600 days in tap water. During this period, potentials of all electrodes in five buffer solutions were measured 44 times. This allowed determining the aging models of the electrodes. Models in other mediums might be different. Changes in slope, standard potential, hysteresis, and linearity of the characteristics were the objects of observations. A method for predicting electrode parameters is proposed. Furthermore, the procedure for estimating the uncertainty of pH measurements considering the aging of the electrodes is described. As a result of this work, a model of the aging process of pH electrodes in tap water can be constructed and subsequently, the measurement accuracy in the periods between calibrations can be improved.

Measurement Uncertainty Calculations for pH Value Obtained by an Ion-Selective Electrode.

An assessment of measurement uncertainty is a task, which has to be the final step of every chemical assay. Apart from a commonly applied typical assessment method, Monte Carlo (MC) simulations may be used. The simulations are frequently performed by a computer program, which has to be written, and therefore some programming skills are required. It is also possible to use a commonly known spreadsheet and perform such simulations without writing any code. Commercial programs dedicated for the purpose are also available. In order to show the advantages and disadvantages of the ways of uncertainty evaluation, i.e., the typical method, the MC method implemented in a program and in a spreadsheet, and commercial programs, a case of pH measurement after two-point calibration is considered in this article. The ways differ in the required mathematical transformations, degrees of software usage, the time spent for the uncertainty calculations, and cost of software. Since analysts may have different mathematical and coding skills and practice, it is impossible to point out the best way of uncertainty assessment-all of them are just as good and give comparable assessments.