Glass pH Research Articles

Improving the Sensitivity of pH Glass Electrodes Towards Ultrasensitive Environmental Monitoring

Improving the Sensitivity of pH Glass Electrodes Towards Ultrasensitive Environmental Monitoring

Increasing the Sensitivity of pH Glass Electrodes with Constant Potential Coulometry at Zero Current.

It has recently become possible to increase the sensitivity of ion-selective electrodes (ISEs) by imposing a constant cell potential, allowing one to record current spikes with a capacitor placed in series in the circuit. The approach requires a transient current to pass through the measurement cell, which unfortunately may introduce measurement errors and additionally excludes the use of high-impedance indicator electrodes, such as pH glass electrodes. We present here an electronic circuit that overcomes these limitations, where the cell is measured at zero current in combination with a voltage follower, and the current spike and capacitor charging occur entirely within the instrument. The approach avoids the need for a counter electrode, and one may use any electrode useful in potentiometry regardless of its impedance. The characteristics of the circuit were found to approach ideality when evaluated with either an external potential source or an Ag/AgCl electrode. The current may be linearized and extrapolated to further reduce the measurement time. The circuit is further tested with the most common yet very challenging electrode, the pH glass electrode. A precision of 64 μpH was obtained for 0.01 pH change up to 0.05 from a reference solution. Similar pH changes were also measured reliably further away from the reference solution (0.5-0.55) and resulted in a precision of 377 μpH. The limitations of this experimental setup were explored by performing pH calibrations within the measuring range of the probe.

Ion-Selective Electrodes With Sensing Membranes Covalently Attached to Both the Inert Polymer Substrate and Conductive Carbon Contact.

The use of solid-contact ion-selective electrodes (ISEs) is of interest to many clinical, environmental, and industrial applications. However, upon extended exposure to samples and under thermal and mechanical stress, adhesion between these membranes and underlying substrates often weakens gradually. Eventually, this results in the formation of a water layer at the interface to the underlying electron conductor and in delamination of the membrane from the electrode body, both major limitations to long-term monitoring. To prevent these problems without increasing the complexity of design with a mechanical attachment, we use photo-induced graft polymerization to simultaneously attach ionophore-doped crosslinked poly(decyl methacrylate) sensing membranes covalently both to a high surface area carbon as ion-to-electron transducer and to inert polymeric electrode body materials (i.e., polypropylene and poly(ethylene-co-tetrafluoroethylene)). The sensors provide high reproducibility (standard deviation of E0 of 0.2 mV), long-term stability (potential drift 7 μV h-1 over 260 h), and resistance to sterilization in an autoclave (121 °C, 2.0 atm for 30 min). For this work, a covalently attached H+ selective ionophore was used to prepare pH sensors with advantages over conventional pH glass electrodes, but similar use of other ionophores makes this approach suitable to the fabrication of ISEs for a variety of analytes.

Ion‐Selective Electrodes With Sensing Membranes Covalently Attached to Both the Inert Polymer Substrate and Conductive Carbon Contact

AbstractThe use of solid‐contact ion‐selective electrodes (ISEs) is of interest to many clinical, environmental, and industrial applications. However, upon extended exposure to samples and under thermal and mechanical stress, adhesion between these membranes and underlying substrates often weakens gradually. Eventually, this results in the formation of a water layer at the interface to the underlying electron conductor and in delamination of the membrane from the electrode body, both major limitations to long‐term monitoring. To prevent these problems without increasing the complexity of design with a mechanical attachment, we use photo‐induced graft polymerization to simultaneously attach ionophore‐doped crosslinked poly(decyl methacrylate) sensing membranes covalently both to a high surface area carbon as ion‐to‐electron transducer and to inert polymeric electrode body materials (i.e., polypropylene and poly(ethylene‐co‐tetrafluoroethylene)). The sensors provide high reproducibility (standard deviation of E0 of 0.2 mV), long‐term stability (potential drift 7 μV h−1 over 260 h), and resistance to sterilization in an autoclave (121 °C, 2.0 atm for 30 min). For this work, a covalently attached H+ selective ionophore was used to prepare pH sensors with advantages over conventional pH glass electrodes, but similar use of other ionophores makes this approach suitable to the fabrication of ISEs for a variety of analytes.

A novel miniaturized pH potentiometric electrode based on a nano bismuth oxide film deposited on a fluorine doped nano tin oxide glass substrate

A novel thin film of bismuth oxide (Bi2O3) deposited on a fluorine doped tin oxide glass substrate (FTO), using a spray pyrolysis technique, was prepared and used as a pH sensing membrane. The deposited Bi2O3 film was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). Film prepared by pyrolysis at 550 °C displayed a tetragonal β-phase of Bi2O3 with a porous structure, high roughness surface and nano cracks. The fabricated Bi2O3/FTO film was used as a miniaturized potentiometric electrode for monitoring a wide range of pH (pH 2 – 12) in aqueous solutions. The electrode exhibited an ideal near-Nernstian response (slope of −60.2 ± 0.3 mV/decade), high potential stability, mechanical durability and good selectivity toward some common interfering cations and anions, supporting its applicability for quality control/quality assurance purposes. The performance characteristics of the electrode and validation measurements, according to the standard methods, were evaluated. The Bi2O3/FTO-based electrode was satisfactorily used for monitoring the pH of some real water, beverages and fruit juice samples and the results compared fairly well with data obtained by the conventional pH glass electrode.

Nafion Modified Titanium Nitride pH Sensor for Future Biomedical Applications.

pH sensors are increasingly being utilized in the biomedical field and have been implicated in health applications that aim to improve the monitoring and treatment of patients. In this work, a previously developed Titanium Nitride (TiN) solid-state pH sensor is further enhanced, with the potential to be used for pH regulation inside the human body and for other biomedical, industrial, and environmental applications. One of the main limitations of existing solid-state pH sensors is their reduced performance in high redox mediums. The potential shift E0 value of the previously developed TiN pH electrode in the presence of oxidizing or reducing agents is 30 mV. To minimize this redox shift, a Nafion-modified TiN electrode was developed, tested, and evaluated in various mediums. The Nafion-modified electrode has been shown to shift the E0 value by only 2 mV, providing increased accuracy in highly redox samples while maintaining acceptable reaction times. Overcoming the redox interference for pH measurement enables several advantages of the Nafion-modified TiN electrode over the standard pH glass electrode, implicating its use in medical diagnosis, real-time health monitoring, and further development of miniaturized smart sensors.

Symmetric cell for improving solid-contact pH electrodes

Traditional pH glass electrodes are designed in a symmetrical manner to guarantee the most reliable and reproducible potentiometric measurements possible. Solid-contact and other pH probes not based on glass membranes are desirable because they allow for new types of applications, may be mass fabricated and less prone to breakage. Unfortunately, however, they introduce electrochemical asymmetry because the reference element used in the reference electrode compartment is now different. This work shows how symmetry may be restored with solid-contact pH probes, using a H+-selective ionophore-based polymeric membrane deposited on top of a conductive polymer (PEDOT-C14) as a transducer layer. The new cell implements a reference element that is composed of a similarly formulated pH probe immersed into a buffer solution and an Ag/AgCl element directly connected to a single-junction Ag/AgCl/3.0 M KCl reference electrode that is placed in contact with the sample solution. By implementing this design, the zero point of the solid-contact pH sensing system may be shifted to the conventional value of pH 7.0. The value of the zero point was experimentally confirmed as 6.96 ± 0.02 pH units at three different temperatures in the range from 5 to 25 °C. This symmetric solid-contact potentiometric cell gave a long-term potential drift of 48 ± 16 μV h−1, comparable to that of a combination pH glass electrode.

Direct Energy Transfer from a pH Glass Electrode to a Liquid Crystal Display.

Self-powered sensors are attractive because the lack of a dedicated battery makes them environmentally friendly and allows them to be more easily miniaturized. Unfortunately, the development of self-powered potentiometric sensors is challenging because only very limited energy can be harvested from this measurement principle. For the first time, the potential of a high impedance glass pH electrode (130 M Ω) is shown here to be directly read out optically. This is accomplished by a liquid crystal display (LCD) as the electrochromic transducer, which changes its transmission upon imposing an external voltage in the range of 2-3 V. Importantly, owing to its low capacitance of about 50 pF, this process requires a very small transient charge on the order of 100 pC, which may be spontaneously imposable even across pH glass electrodes. For the LCD to be turned on, the cell voltage is boosted by additional Zn2+/Zn elements placed in series. The LCD is found to give a time-dependent absorbance decrease, which is mitigated by adding a high resistance element to attenuate the associated decay. The approach gives repeatable LCD absorbance values that allows one to directly visualize pH with a precision of about 0.01 pH units. The absorbance value depends inversely on pH in a much wider range (pH 1-13) than what is normally observed with optical sensors while based on the same underlying measurement as a potentiometric pH probe.

John W. Severinghaus, M.D., 1922 to 2021.

John W. Severinghaus, M.D., 1922 to 2021.

Natural emulsifier assisted lubricity of the colloidal system: Effect of natural emulsifier concentration

Environmental needs, human health issues, government regulations have motivated this work to explore an alternative to mineral oil-based systems to vegetable oil-based environmental friendly lubricants. The present study is an attempt to use natural products (soybean oil and Gum Arabic) to develop environmental friendly oil-in-water emulsion to be used as metalworking fluid. The role and effect of Gum Arabic (GA) concentration on emulsion stability, wettability, and lubricity is explored. Three concentrations of GA corresponding to critical micelle concentration (CMC), below CMC and above CMC are selected to formulate the emulsions (Formulated fluids (FFs)). The emulsion characteristics (droplet size and zeta potential), pH, wetting dynamics, and lubricity are evaluated using dynamic light scattering (DLS), pH glass electrode, Goniometer, and four-ball tester (FBT), respectively. Worn surfaces are analysed using Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscope (FESEM). The physical characteristics and tribological responses suggest that the FF @ CMC of GA exhibited better stability, lubricity, and antiwear properties than other formulations. Different responses of FFs are benchmarked with that of mineral oil-based commercial fluid (CF). FF @ CMC of GA showed a better anti-friction and similar anti-wear response as compared to CF. The excellent lubricity of the FF @ CMC of GA is attributed to the formation of the low shear strength stable lubricious film due to the active participation of GA molecules at the tribo-pair interface.

Monitoring pH Using Alizarin-modified Commercial Screen-printed Electrodes

A pH-sensor based on alizarin-modified screen-printed multiwalled carbon nanotubes (MWCNT-SPE, Orion High Technologies) imbedded in Nafion® shows a linear dependence between the oxidation potential and the pH from pH 0 to pH 10. This modified MWCNT-SPE is compared to a commercial alizarin SPE (DRP 110ALI, Metrohm - DropsSens). In addition to this technical application, these pH sensors seem to be a good didactic alternative to the widely used pH glass electrode, which many students find hard to understand.

Aeration-induced marine sediment acidification in the vicinity of Rizhao Port, western Yellow Sea

Two short-term summer cruises were performed in the vicinity of Rizhao Port, western Yellow Sea, to investigate summer water stratification and the phenomenon of marine sediment acidification. Results show that water stratification has formed as early as in May. The chemoclines of dissolved oxygen (DO) and pH usually occur deeper than the thermocline. Sometimes the chemoclines of DO and pH occur synchronously at the same depths, but sometimes they do not synchronize. Above the chemocline DO fluctuates markedly and maintains at a high level or even oversaturation in daytime, suggesting the far-field impact of vessel propulsion. Below the chemocline it invariably remains at a low and stable level and slowly drops downward. The pH values of surface sediments vary in the range of 6.3–7.6. A conspicuous sediment acidification is observed along the navigation region. This phenomenon is chiefly attributed to the intermittent disruption of summer stratification by shipping activity along the shipping channel and waterways. Water stratification precludes the penetration of DO down to the bottom sediments on fair ocean status, and maintains anoxia below the sediment–water interface, whereas the abrupt DO increase driven by propeller agitating is nearly restricted in the navigation area. Therefore, the aeration effect accelerating oxidation of reducing substances and organic matter is primarily responsible for enhanced acid accumulation in surface sediments. In addition, the suspension effect is identified by the negative offsets of zero point on pH–mV diagram. Most of the measured points are scattered correspondingly on three distinct regression lines, with similar slopes but different negative offsets of pH 6.53, 6.87, and 6.99, respectively. Their geographical distribution suggests that this effect has a positive relationship with the intensity of anthropogenic disturbance. Although the suspension effect is caused by the adsorption of charged particles at the pH glass electrode interface (Yang et al. in Part Sci Technol 7:139–152, 1989), its various intensity observed in practice may also reflect the inherent distinction of depositional environments in physicochemical conditions.

Voltammetrically Measuring pH of Strong Basic Solution on Au Electrode Modified with Ag3PO4 Shell@Ag Core Nanoparticles

AbstractPrecise determination of pH values of strong basic solution is appealing and challenging. Herein, a voltammetric method for measuring pH of strong basic solution was developed using Ag3PO4 shell@Ag core nanoparticles as a pH indicator. Ag nanoparticles (AgNPs) were electrodeposited on Au electrode surface and then were electrochemically oxidized to form Ag+. A layer of Ag3PO4 was in‐situ formed on the surface of AgNPs by precipitation with PO43− in solution. As an electroactive species, Ag3PO4 can undertake an electrochemical redox reaction and its reduction peak potential is linear with pH values of solution in the range of 10–14. The slope of the linear equation is about −0.0196, which is consistent with that calculated by the Nernst equation. The resultant AgNPs/Ag3PO4 modified electrode has been successfully applied in the determination of pH of strong basic solution. The proposed voltammetic method for measuring pH value overcomes the shortcoming of pH glass electrode under strong basic environments.

Sensor and sensor microtiterplate with expanded pH detection range and their use in real samples

An improved pH indicator derived from a new design concept for luminescent europium complexes and its favourable properties in wide-range pH sensors are introduced. By decorating Eu3+ with ligands that display widespread pKa values and an antenna ligand, this probe covers a dynamic range up to 8 pH units. Unlike wide-range pH sensors that employ multiple organic dyes with multiple pKa values, our concept requires almost no synthetic effort and only one excitation and emission wavelength which simplifies the instrumental requirements. The improved indicator only uses the chelators theonyl trifluoroacetone (TTA) as antenna ligand and pyridine dicarboxylic acid (PDA). The luminescence emission of the Eu3+-TTA-PDA complex in a 1:3:2 feed ratio in aqueous buffer is dependent of pH from pH 2–10. Sensor membranes containing Eu3+-TTA-PDA respond continuously and reversibly from pH 2–8 over 6 pH units in few minutes. This range is one order of magnitude wider than that of a previous lanthanide indicator. Additionally, we fabricated a high-throughput pH sensor microtiterplate with a dynamic range from pH 2–8 over 6 pH units. It constantly works up to 24 h. Finally, we demonstrate that the pH of some real samples taken with the sensor microtiterplate agrees well with the pH obtained by a pH glass electrode.

Simple and Economical Procedure To Assemble pH Glass Membrane Electrodes Used in Chemical Education

The stated purpose of this paper is to provide a simple and quick method to assemble pH electrodes using readily available materials. The present assembled electrodes are comparable with commercial pH electrodes, with accuracy for pH determination in the range 2–12. Furthermore, the constructed simple pH electrodes exhibit a fast and stable response with a relatively wide linear range, meaning that these electrodes offer the promise of potential utilization in experiments. The inexpensive assembly and use of these pH glass membrane electrodes lends itself to introductory electrochemistry lab experiments at only a fraction of the cost of commercial electrodes. Under the guidance of instructors, students could make and test their own electrodes for chemical experiments. This might be helpful for students to gain a deeper understanding of the fundamentals of electrochemistry, such as the structure of ion-selective electrodes, the Nernst equation, etc.

Smart pH Sensor Using Untreated Platinum Sheet Based on Chronopotentiometry and Long-Term Stability Analysis

In this paper, we design a smart pH sensor using untreated platinum sheet based on chronopotentiometry. This novel pH sensor is very suitable for applications in the deep sea, highly polluted water, and other harsh environments, where maintenance is difficult. In order to verify the long-term monitoring stability of the pH sensor, 17-day monitoring experiments are conducted in river water. We draw some conclusions for the properties of the pH sensor. First, the pH values obtained from the positive current agreed well with the pH glass electrode, indicating that it is suitable for pH monitoring. Moreover, the deviation derived from hysteresis is small. Second, the pH values obtained from the negative current could not reflect the actual pH of river water in long-term measurement. There may be two reasons for this: the changing conductivity in the river water and the unstable composition of the platinum sheet. Third, the conductivity may have an obvious impact on the potential obtained from the negative current; the electrochemical reaction where Pt is oxidized to PtO may be influenced by the ionic strength of the solution. Therefore, the pH values obtained from the positive current is more suitable for long-term pH monitoring.

Preparation and Optimization of Optical pH Sensor Based on Sol-Gel.

Making use of the sol-gel technique, an optical pH sensor was prepared, which was made from an organic carrier with four indictors including congo red, bromophenol blue, cresol red, and chlorophenol red, cross-linked by tetraethyl orthosilicate (TEOS) and cellulose acetate. The actual detection range of the optical pH sensor is 2.5–11.0. The optimal ratio of ethyl orthosilicate, absolute ethanol, deionized water, and hydrochloric acid in glue precursor of the sensor-sensitive membrane was explored. The orthogonal experiment was designed to optimize the dosage of cellulose acetate, N,N-dimethylformamide (DMF), indicator, hydrochloric acid, and precursor glue in preparing the sensor-sensitive membrane. The linearity, measurement accuracy, repeatability, stability, and response time of the prepared pH sensor were tested. The measurement results were analyzed using a support vector machine and linear regression. The experimental results show that the optical pH sensor has a measurement accuracy of up to 0.2 pH and better stability and repeatability than the traditional pH glass electrode.

Study for developing an electronic tongue to discriminate three different classes of waters, by using common sensors and the principal component analysis

ABSTRACTA basic research has been carried out using four probes to develop an electronic tongue able to discriminate three different kinds of natural waters, i.e. rain, river and groundwater. Several natural water samples were analysed to this purpose using a pH glass electrode, a digital (thermistor) thermometer, an amperometric gaseous diffusion oxygen sensor for measuring the dissolved oxygen and a direct methanol fuel cell enzymatic probe for measuring the concentration of alcoholic traces. Data were processed by means of principal component analysis, obtaining three well differentiated clusters, that demonstrate how the use of only four different sensors can discriminate in an inexpensive and effective way three different classes of natural waters.

Effect of Exposed Surface Area, Volume and Environmental pH on the Calcium Ion Release of Three Commercially Available Tricalcium Silicate Based Dental Cements.

Tricalcium silicate cements (TSC) are used in dental traumatology and endodontics for their bioactivity which is mostly attributed to formation of calcium hydroxide during TSC hydration and its subsequent release of calcium and hydroxide ions. The aim of this study was to determine the effect of volume (Vol), exposed surface area (ESA) and pH of surrounding medium on calcium ion release. Three commercially available hydraulic alkaline dental cements were mixed and condensed into cylindrical tubes of varying length and diameter (n = 6/group). For the effect of ESA and Vol, tubes were immersed in 10 mL of deionized water. To analyze the effect of environmental pH, the tubes were randomly immersed in 10 mL of buffer solutions with varying pH (10.4, 7.4 or 4.4). The solutions were collected and renewed at various time intervals. pH and/or calcium ion release was measured using a pH glass electrode and atomic absorption spectrophotometer respectively. The change of pH, short-term calcium ion release and rate at which calcium ion release reaches maximum were dependent on ESA (p < 0.05) while maximum calcium ion release was dependent on Vol of TSC (p < 0.05). Maximum calcium ion release was significantly higher in acidic solution followed by neutral and alkaline solution (p < 0.05).

Relationship between surface μ‐roughness and interface slurry particle spatial distribution during glass polishing

AbstractDuring optical glass polishing, a number of interactions between the workpiece (i.e., glass), polishing slurry, and pad can influence the resulting workpiece roughness at different spatial scale lengths. In our previous studies, the particle size distribution of the slurry, the pad topography, and the amount of material removed by a single particle on the workpiece were shown to strongly correlate with roughness at AFM scale lengths (nm‐μm) and weakly at μ‐roughness scale lengths (μm‐mm). In this study, the polishing slurry pH and the generation of glass removal products are shown to influence the slurry particle spatial and height distribution at the polishing interface and the resulting μ‐roughness of the glass workpiece. A series of fused silica and phosphate glass samples were polished with various ceria and colloidal silica slurries over a range of slurry pH, and the resulting AFM roughness and μ‐roughness were measured. The AFM roughness was largely invariant with pH, suggesting that the removal function of a single particle is unchanged with pH. However, the μ‐roughness changed significantly, increasing linearly with pH for phosphate glass and having a maximum at an intermediate pH for fused silica. In addition, the spatial and height distribution of slurry particles on the pad (as measured by laser confocal microscopy) was determined to be distinctly different at low and high pH during phosphate glass polishing. Also, the zeta potential as a function of pH was measured for the workpiece, slurry, and pad with and without surrogate glass products (K3PO4 for phosphate glass and Si(OH)4 for silica) to assess the role of interfacial charge during polishing. The addition of K3PO4 significantly raised the zeta potential, whereas addition of Si(OH)4 had little effect on the zeta potential. An electrostatic DLVO three‐body force model, using the measured zeta potentials, was used to calculate the particle–particle, particle–workpiece, and particle–pad attractive and repulsive forces as a function of pH and the incorporation of glass products at the interface. The model predicted an increase in particle–pad attraction with an increase in pH and phosphate glass products consistent with the measured slurry distribution on the pads during phosphate glass polishing. Finally, a slurry “island” distribution gap (IDG) model has been formulated which utilizes the measured interface slurry distributions and a load balance to determine the interface gap, the contact area fraction, and the load on each slurry “island”. The IDG model was then used to simulate the workpiece surface topography and μ‐roughness; the results show an increase in roughness with pH similar to that observed experimentally.