Combination electrodes

Glass membrane pH electrodes are often available in a combination form that includes both the indicator and the reference electrode. The use of a single electrode greatly simplifies the measurement of pH. An example of a typical combination electrode is shown in Figure 11.12. 

Combination electrodes have increased in use and are a consoHdation of the glass and reference electrodes in a single probe, usually in a concentric arrangement, with the reference electrode compartment surrounding the pH sensor. The advantages of combination electrodes include the convenience of... 

Glass electrodes are now available as combination electrodes which contain the indicator electrode (a thin glass bulb) and a reference electrode (silver-silver chloride) combined in a single unit as depicted in Fig. 15.2(h). The thin glass bulb A and the narrow tube B to which it is attached are filled with hydrochloric acid and carry a silver-silver chloride electrode C. The wide tube D is fused to the lower end of tube B and contains saturated potassium chloride solution which is also saturated with silver chloride it carries a silver-silver chloride electrode E. The assembly is sealed with an insulating cap. 

So-called combination electrodes may be purchased in which the glass electrode and the saturated calomel reference electrode are combined into a single unit, thus giving a more robust piece of equipment, and the convenience of having to insert and support a single probe in the test solution instead of the two separate components. 

Chronocoulometry, 62 Clark electrode, 190 Coated wire electrodes, 160 Cobalt, 82, 85 Cobalt phthalocyanine, 121 Collection efficiency, 113, 135 Collection experiments, 113 Combination electrode, 148 Compact layer, 19 Composite electrodes, 47, 114, 133 Computer control, 80, 106 Concentration profile, 7, 9, 11, 29, 36, 87, 132... 

Another version of cell or group arrangement is that using bipolar electrodes (Eig. 18.1a). Here, combined electrodes are used One side of the electrode functions... 

Gas-sensing electrodes. A gas-sensing electrode consists of a combination electrode that is normally used to detect a gas in its solution by immersion. The sensor contains the inner sensing element, usually a glass electrode or another ISE, and around this a layer of a 0.1 Af electrolyte, surrounded by a gas-permeable membrane. On immersion of the sensor this membrane contacts the solution of the gas which diffuses through it until an overall equilibrium is established, i.e., the partial pressure of the gas attains an equilibrium between sample solution and membrane and between membrane and sensor electrolyte. For a better understanding of the interaction between this electrolyte and the... 

Most manufacturers not only have taken the above requirements and possibilities into account, but also deliver for convenience combined electrodes that contain both the indicator and reference electrodes this is the case for glass electrodes (see Fig. 2.13) and other ISEs as well as for redox electrodes. 

Note from the definition is follows that the pH of the isotherm intersection point in Fig. 2.13 represents the isopotential pHf of the Metrohm EA121 combined electrode.)... 

Input international BNC sockets for pH, glass or combination electrodes, 4-mm sockets for RE electrode and Pt 100 input at 25° C, current <0.1pA, resistance > 1013Q. 

In most experiments the smallest amount of electrolyte needed to coagulate the sols measured after 2 hours standing was chosen as the CCC. When using HC1, this point is the critical coagulation pH. A constant temperature water bath was used for temperature different than 23°C. The pH values were measured with a Beckman Model 96A pH meter and a Fisher combination electrode. The electrophoretic mobility measurements were made with a Laser Doppler Electrophoresis apparatus. These experiments were performed by Mr. J. Klein of the Chemistry Department, Syracuse University. 

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. 

Comb copolymers, 7 610t Combed yarn, 11 178 Combes synthesis, of quinolines, 21 189 Combicat, 7 387, 392 Combinational libraries, 7 382 characterization, 7 404-405 composition gradient libraries, 7 407 design, 7 399-400 fabrication, 7 414-419 temperature gradient libraries, 7 407—408 thickness gradient libraries, 7 406 Combination electrodes, 14 30 Combination vaccines, 25 504-505 Combinatorial biology, 16 414 Combinatorial biosynthesis, 15 301-302, 305... 

Figure 9.6. A—temperature electrode B—reference electrode suitable for ISE measurements C—nitrate ISE electrode D—combination electrode E—conductivity electrode.

Fouling of the reference electrode or the reference side of a combination electrode is a common problem in soil pH measurements. Fouling can be caused by salts, organic matter, and clay. Each electrode manufacturer will provide specific cleaning procedures that help to keep electrodes functioning properly however, in many cases, no amount of cleaning is effective and the electrodes need to be replaced. 

As mentioned previously, electroanalytical techniques that measure or monitor electrode potential utilize the galvanic cell concept and come under the general heading of potentiometry. Examples include pH electrodes, ion-selective electrodes, and potentiometric titrations, each of which will be described in this section. In these techniques, a pair of electrodes are immersed, the potential (voltage) of one of the electrodes is measured relative to the other, and the concentration of an analyte in the solution into which the electrodes are dipped is determined. One of the immersed electrodes is called the indicator electrode and the other is called the reference electrode. Often, these two electrodes are housed together in one probe. Such a probe is called a combination electrode. 

A combined electrode is a double electrode system consisting of a clast- electrode. md. 1 calomel electrode combined in one probe. 

Metrohm Herisau Prazisions-pH meter E 510 and combined electrode were used for the potentiometric titrations and electrode was filled with saturated solution of potassium chloride in water free methanol instead of aqueous potassium chloride. 

Figure 7.40 Polarization curves of sphalerite combination electrode in different pH media (KNO3 0.1 mol/L NaOH 2 x 10" mol/L unit of I A/cm )...

Figure 7.41 is the polarization curves of sphalerite-carbon combination electrode in different collector solution at natural pH. The corrosive electrochemistry parameters are listed in Table 7.8. These results show that xanthate and dithiocarbamate have distinctly different effects on sphalerite. The corrosive potential and current of sphalerite electrode are, respectively, 42 mV and 0.13 pA/cm at natural pH in the absence of collector, -7 mV and 0.01 pA/cm in the presence of xanthate, and 32 mV and 0.12 pA/cm in the presence of dithiocarbamate. The corrosive potential and current decrease sharply with xanthate as a collector, indicating that the electrode surface has been totally covered by the collector film from the electrode reaction. Xanthate has big inhibiting corrosive efficiency and stronger action on sphalerite. However, the corrosive potential and current of sphalerite electrode have small change with dithiocarbamate as a collector, indicating that DDTC exhibits a weak action on sphalerite. 

Figure 3.9 Schematic diagrams of pH electrodes, showing (a) a glass electrode, and (b) a pH combination electrode (note that the glass and the bulb are the same in both cases).

Measurements with pH or glass electrodes are very similar experimentally, with the only real difference being the exact position of the reference electrode, i.e. either within the electrode housing (in a pH combination electrode, as shown in Figure 3.9(b)) or wherever the experimenter decides to place it (using a glass electrode). 

We then described how ion-selective electrodes (ISEs) function by means of generating an emf that is related to the activity of a single ion. The simplest ISEs are glass electrodes for pH determination, and the related pH combination electrodes. Other solid-state ISEs, such as the fluoride electrode, function in the same way. 

This was followed by titration with 0. IN trifluoromethyl sulfonic acid, and the end-point was detected with the use of a glass Ag/AgCl combination electrode [80]. 

The measurement of pH is carried out using a sensing electrode, which is sensitive to hydrogen-ion activity and a reference electrode. Combination electrodes incorporating both of these electrodes are also suitable for most applications. Separate reference and sensing electrodes are normally used only for high-precision research applications. 

Figure 15.2. Design of the combined electrode. 1, Internal reference electrode, usually Ag AgCl 2, outer glass membrane 3, inner glass membrane 4, external reference electrode, usually Ag AgCl 5, diaphragm.

---