Combination pH electrodes

The bulb is usually fabricated with common soda glass, i.e. glass containing a high concentration of sodium ions. Finally, a small reference electrode, such as an SCE, is positioned beside the bulb. For this reason, the pH electrode ought properly to be called a pH combination electrode, because it is combined with a reference electrode. If the pH electrode does not have an SCE, it is termed a glass electrode (GE). The operation of a glass electrode is identical to that of a combination pH electrode, except that an external reference electrode is required. 

A combination pH electrode is the most commonly used electrode to determine soil pH. It is illustrated in Figure 9.5 and shown in Figure 9.6 (D), which shows the pH sensing bulb and reference side. As an alternative to the... 

Figure 9.5. Typical setup for a combination pH electrode. Note ( ) that the saturated KCI/AgCl solution can be different depending on the electrode manufacturer.

Note This experiment calls for you to use a pH meter and a combination pH electrode (Chapter 14) to... 

Prepare the pH meter and a combination pH electrode. Place the electrode in the beaker such that the tip of the electrode is immersed, but suspended with a clamp or pointed to the side of the beaker to avoid contact with the stirring bar. You may have to add some distilled water in order for the tip (including the contact to the reference electrode) to be completely immersed. 

In order to use the pH electrode described above, two half-cells (probes) are needed—the pH electrode itself and a reference electrode, either the SCE or the silver-silver chloride electrode—and two connections are made to the pH meter. An alternative is combination pH electrode. This electrode incorporates both the reference probe and pH probe into a single probe and is usually made of epoxy plastic. It is by far the most popular electrode today for measuring pH. The reference portion is a silver-silver chloride reference. A drawing and a photograph of the combination pH electrode is given in Figure 14.7. 

FIGURE 14.7 Left, a drawing of a commercial combination pH electrode. Right, a photograph of a commercial combination pH electrode. In the photograph, notice the silver electrodes in both the inner and outer tubes. 

FIGURE 14.9 Photographs of the electrical connections to the combination pH electrode. Left, the bnc type of connection. Right, two separate connections to be made to the pH meter. 

Prepare a pH meter and combination pH electrode with a pH = 7 buffer. 

Obtain and clean 12 test tubes large enough to be able to dip a combination pH electrode into a solution held inside it. Also obtain one or two test tube racks to accommodate the 12 test tubes. Label ten of the test tubes as follows pH3, pH4, pH5, pH6, pH7, pH8, pH9, pHIO, pHll, and pH12. Label the remaining two as follows 0.5 M HC1 and 0.5 M NaOH. Fill these with the appropriate solutions. Place all test tubes in the rack. 

A combination pH electrode consists of a pH electrode and a reference electrode in a single probe. 

Figure 15-24 (a) pH-sensitive field effect transistor, (b) Combination pH electrode based on field effect transistor. The thermistor senses temperature and is used for automatic temperature compensation. [Courtesy Sentron. Federal Way, WAJ... 

B. 13-Isovalerolactam. A 200-ml. beaker is provided with a combination pH electrode, a mechanically driven paddle stirrer, a thermometer, and a syringe or dropping funnel (Note 9). An amount of water just sufficient for immersion of the pH electrode (20 ml.) is introduced, and with vigorous stirring the first portion... 

Materials. Trimethylamine N-oxide dihydrate (98%) from Aldrich and N-dimethyldodecylamine N-oxide (97%) from Fluka Chemie were used as received. N-dimethylhexylamine N-oxide and N-dimethyloctylamine N-oxide were prepared by reaction of the corresponding tertiary amine with hydrogen peroxide (12). Both samples were isolated as crystalline solids and were >99% pure, based on acid/base titrations and spectrometric methods. Both samples were very hygroscopic. Reagent grade NaBr, 0.1 N and 2.0 N HC1 were from J.T. Baker Chemical Co. and the all solutions were prepared using distilled and deionized water. The pH was monitored using an Orion Ross combination pH electrode and an Orion EA 940 meter. 

Figure 11. Electrodes in microcalorimetric vessels. A Schematic diagram of a section through a titration-perfusion microcalorimetric vessel equipped with a polarographic oxygen electrode and a pH electrode, a, sample compartment, volume 3 ml b, hollow stirrer shaft c, steel tube d, turbine stirrer e, O-rings f, combination pH electrode protected by a steel tube g, polarographic oxygen sensor (Clark electrode). B Record from a growth experiment with T-lymphoma cells. The vessel was completely filled with medium. Once the baseline had been established, the experiment was started (as indicated by the arrow) by the injection of 100 pi concentrated cell suspension.

Kilic et al. selected five different antibiotics, including ciprofloxacin, and reported a titration method based on the use of tetrabutylammonium hydroxide as the titrant in a non-aqueous assay method [6]. Ciprofloxacin was dissolved in water and diluted to 25 mL with pyridine. A 20 mL portion of the resulting solution was titrated with 0.04 M tetrabutylammonium hydroxide in methanol/propan-2-ol at 25°C under nitrogen in a jacketed glass reaction cell. End-point detection was performed with an Orion 720A digital pH ion-meter, equipped with a combination pH electrode that contained a saturated solution of anhydrous methanolic KC1 in the reference. The method was applied to pharmaceutical preparations, and enabled recoveries in the range of 99.95-101.53%, with a RSD of 0.5-1.09%. 

Assay (Note Use a combination pH-electrode for all titrations.) Dissolve 0.100 to 0.150 g of sample, accurately... 

Assay (Note Use a combination pH-electrode for all titrations.) Accurately weigh between 0.100 and 0.150 g of sample, and dissolve it in 50 mL of ethanol. Perform the titration under a flow of nitrogen. Titrate with standardized 0.1 A tetrabutylammonium hydroxide in methanol or 2-propanol. Determine the volume of titrant needed to reach the first equivalence point (Vi mL) and the second equivalence point (V2 mL). 

Turbidimetric titrations were conducted in three ways. In "Type 1" titrations, a mixture of PDMDAAC (0.04-4.0 g/L) and protein (0.1-10 g/L) were combined at pH 4 in distilled deionized water or dilute (0.05-0.5M) NaCl. The optical probe (2 cm path length) of a Brinkman PC600 probe colorimeter (240 nm), and a combination pH electrode connected to an expanded scale pH meter (Orion 811 or Radiometer pH M26), were both placed in the solution. Titrant (0.50 M NaOH or 0.50 M HC1) was delivered from a 2.0 mL microburet (Gilmont) with gentle stirring. Alternatively, turbidity was monitored while a protein solution was added to PDMDAAC (at constant ionic strength) or vice-versa. Turbidity was reported as 100-96T, which is linearly proportional to the absolute turbidity in the range 80<%T<100. 

Measurement of pH can be made in the NMR tube by using a micro combination pH electrode of approximately 3 mm diameter. For adjustment of pH in D2O solutions, DCl, D2SO4, DCIO4 and/or NaOD solutions are used. The... 

Expression (5.7) is, in fact, built into the routine measurement of pH with a commercial pH meter. Such meters have a scale graduated in pH units, obviating the need to convert volts to pH units. Prior to pH measurement, the buffer solution and unknown solution are brought to the same temperature. The temperature compensation dial on the meter is then turned to that temperature. This sets the meter with the appropriate Nernst-factor value for pH respon.se at the temperature of measurement. The pH and reference electrode pair (preferably available in a single, combination pH electrode) are then immersed in a buffer solution of known pH, and the meter is set to that pH. Immersion of the electrodes in the unknown solution then yields that solution s pH. 

Fig. 2-4. Typical batch reactor configuration. pH is controlled by a combination pH electrode and automatic buret connected to an autotitrator a syringe sampler allows for removal of a subsample of suspension an addition port permits injection of solute an inert gas is bubbled through the suspension by means of a gas dispersion tube and the system is vented through a gas trap a thermometer allows for temperature monitoring and the suspension is mixed with an overhead stirrer.

Start with one of the known acids. Using a graduated cylinder, add 25 mL of the 0.05 M acid to the 250-mL beaker. Place the tip of the combination pH electrode into the beaker such that it is out of the way of the stirring bar. You may need to add some distilled water in order to be sure that the contact to the inside of the electrode is immersed. Start the stirrer. Measure the pH of the solution in the beaker. Record it in your table as the pH for 0.00 mL NaOH added. Fill the buret with the NaOH solution such that the bottom of the meniscus rests on the 0.00 mL graduation line or, if the meniscus is below the 0.00 mL line, record the reading to the nearest 0.01 mL. 

Fig. 7.2 Measurement of pH using a combination pH electrode and meter. The electrical potential difference recorded by the potentiometer is directly proportional to the pH of the test solution.

A microbial electrode consisting of a bacteria-collagen membrane reactor and a combined pH electrode for cephalosporins in a fermentation broth are described here. It was found that... 

Phosphate buffer (0.5 mM, pH 7.2) was transferred continuously to the reactor and sensing chamber. Then, 10 ml of sample solution containing various amounts of cephalosporins was transferred to the reactor at a flow rate of 2 ml/min by a peristaltic pump and the hydrogen ion concentration in the sample solution was determined by a combined pH electrode (GC-125 C, TOA Electronics Co. Tokyo) and displayed on a recorder (Model CDR-llA, TOA Electronics Co.). 

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