Combined glass electrodes

Whether the assumption about this linear relationship can be used for the zero shift as such is doubtful the situation becomes more reliable if the internal and external reference electrodes are equal so that E°mer and °uter cancel, hence eqn. 2.95 becomes En = (- 2.3026RT/F) pHinncr. Therefore, the zero shift can be eliminated instrumentally by setting the mechanical zero of the pH meter to pHjnncr (if previously known). With a non-combined glass electrode the external... 

SO Electrode. A gas-sensing SO2 electrode marketed by Ionics, Inc. was used to provide additional VLE data at 25°C as a function of composition. Aqueous SO2 equilibrates across a polymeric membrane with a filling solution containing about 0.1 M NaHSO-j. Ionic species do not diffuse across the membrane. A small combination glass electrode measures the pH of the filling solution. The SO2 activity (Pso ) is proportional to the activity of H+ (10"PH), because the bisulfite activity is constant ... 

Cephalosporin is determined from the proton concentration generated in a medium by using immobilized bacteria. A microbial sensor composed of a bacteria-collagen membrane reactor and a combined glass electrode was applied to the determination of cephalosporins in fermentation media. The system used for continuous determination... 

Figure 4. Immobilized whole cell-based flow-type sensor for cephalosporins. 1. Soda lime 2. Buffer reservoir 3. Peristaltic pump 4. Sample inlet 5. Immobilized whole cell reactor 6. Combined glass electrode 7. Sensing chamber 8. Amplifier 9. Recorder...

Scheme of the detection cell of the hydrogen peroxide sensor expanded with the FIA system. The inner chamber has a 20-cm length and a 1-cm diameter (1) working electrode, (2) reference electrode, (3) counter electrode, (4) combined glass electrode, and (5) temperature sensor, surface of the working electrode equals 7 mm2. 

The pH measurements are carried out with a Crison micropH 2001 pH-meter with an Ingold combined glass electrode. All the experiments are done at room temperature (25 + l°C). 

With this apparatus, constant pH can be maintained by using a combination glass electrode along with an automatic titrimeter and digital buret. 

The use of pressurized, sterilizable combined glass electrodes mounted through the reactor vessel wall is widely established. A high degree of accuracy and stabihty is needed to provide a good basis for the control loop. However, a recahbration is necessary both after sterilization and at regular intervals. This is easily done by external measurement after sampling the reactor, because the pH of the sample drifts very slowly. 

All chemicals were reagent grade, and the solutions were prepared with high-purity water from a Millipore system. The pH measurements were carried out with a combined glass electrode (Metrohm) standardized with pH-buffer solutions (Merck). The lepidocrocite suspensions were prepared according to the procedure developed by Brauer (21) by oxidation of a FeCL2 solution with NaNOa as the oxidant, in presence of hexamethylenetetramine at 60 °C for 3 h. To remove excess chloride, the lepidocrocite suspensions were washed sev-... 

Potentiometric study. pH measurements were effectuated using pH stat TITRINO titrimeter with a combined glass electrode saturated with KCl. 

Weigh into a 250 mL beaker a sample close to but not less than 5.0 g. Record the weight to the third decimal place. Add 125 mL of distilled water and stir magnetically and briskly until the a smooth suspension is obtained (about 5 minutes). Immerse a calibrated (4.00 and 7.00 />H) combination glass electrode in the solution, making sure that, when stirring, the reference compartment frit... 

For the preparation of aluminate coatings, the deionized water was preheated with an electric heater under constant stirring to the desired temperature, a zirconia disc was inserted and then the AIN powder added to the water. The pH and temperature were measured versus time using a combined glass-electrode/Pt 1000 thermometer pH meter (Metrohom 827). In addition, some of the prepared boehmite coatings on zirconia surface were thermally treated in the resistance oven in dry air, at 900 °C, for 1 hour, at a heating rate 10 °C/min. 

All photometric measurements were made witii a Bausch and Lomb Spectronic 2000 instrument. Matched silica cuvettes were used in all measurements and tiie li t path was 10 mm. The pH was measured with a Crison Model 501 pH meter fitted witii a combined glass electrode. The pH meter was standardised against 0.05 M potassium hydrogen phtiialate (pH = 4.01 at 25 °C). Solutions for absorbance and pH measurements were prepared by mixing 2 mL of 2 x 10 M stock solution of isonicotinic acid in water, 2.5 mL of sodium perchlorate and a few drops of sodium hydroxide or perchloric acid at different concentrations. The solutions were then diluted to 25 mL with distilled water. Absorbance was measured against a solvent blank and the pH checked after the absorbance measurements. The temperature was kept at 20 1 °C."... 

The ORION 701/Digital pH meter was used for all ion selective electrode measurements in order to employ an expanded scale, whereas pH measurements were recorded on an ORION 601/digital ionalyzer. The Model 476050 Corning single pH reference combination glass electrode was used for the measurement of the hydrogen ion activity. 

Fig.9. a) Schematic diagram of the measurement unit 1. solution dispensers, 2. measuring cell, 3. inner cell, 4. membrane, 5. combination glass electrode, 6. reference filling solution, 7. temperature sensor, b) 1. Block diagram of the pH monitor 1. measurement unit, 2. buffer I, 3. buffer II, 4. rinsing solution, 5. local control, 6. preamplifier, 7. readout / transmitter. 

Stacking gel buffer solution 0.5 M Tris-HCl, pH 6.8, containing 0.4% (w/v) SDS. Dissolve 6.05 g of Tris and 400 mg of SDS in 90 ml of water. Titrate solution at room temperature to pH 6.8 with 6 N HCl using a combination glass electrode. Complete with water to 100 ml. Keep solution at room temperature. 

Figure 5 shows a scheme of a typical Severinghaus sensor for PCO2 measurements in blood. The major components of this sensor are a pH-sensitive combination glass electrode, a thin electrolyte layer (bicarbonate solution), and a polymer membrane permeable for CO2 [20]. If a flowing solution of blood sample passes the sample channel, CO2 permeates the membrane and dissolves in the thin electrolyte layer of bicarbonate solution. In this way the following equilibrium is influenced ... 

The CO2 diffusing into the internal electrolyte results in a pH change recorded with the combination glass electrode. The pH change correlates with the pC02. Theoretically calculated pH values as a function of PCO2 with different NaHCOs concentrations of the electrolyte solution are shown in Fig. 6. 

The potential of such electrodes depends on the activity of a specific ion. The most widely used is the glass electrode. This consists of a tube ending in a special glass bulb filled with a O.IM HCI in which a Ag/AgCI electrode is inserted. The special glass is sensitive to H ions and is specific for pH measurements. A combined glass electrode is often used in which a calomel electrode is coupled with the glass electrode. The... 

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