Sleeve junction

PH electrodes from Crison, combination electrodes that contain a built-in temperature probe, a bridge electrolyte chamber and movable sleeve junction from Mettler, and combination pH puncture electrodes with spear-shaped tip from Mettler are some commercially available pH measurement systems for semisolid formulations. 

A more definitive test for a clogged junction is a resistance measurement. A reference junction which exhibits the typical difficulties encountered with a large liquid junction potential (see Figure 3.8) may have a large resistance. When a reference electrode is made, the manufacturer will often test the resistance of the junction. A new asbestos or quartz fiber junction may have a resistance of 5000 ohms. A new annular ceramic or sleeve junction has less resistance. With use and aging, the resistance value often... 

Use an electrode pair or a combination electrode with a ceramic, quartz, or sleeve junction. 

The proper selection of electrodes is discussed in Chapter 3. The primary concern is to select a reference electrode which provides a stable liquid junction potential in the sample. With limited sample volume, the combination electrode is often required, but an electrode pair with a sleeve junction reference is frequently used in a colloidal sample because of its low junction resistance and ease of cleaning (see Figure 6.3). 

The methods of reducing the liquid junction potential have already been discussed in Chapter 3. Basically, they include proper selection of the junction or altering the filling solution. Most often, a sleeve junction reference electrode will afford the greatest stability and the least junction potential in this type of sample. It is also very easy to clean, which becomes important with a sticky-type sample that is apt to clog the normal fiber-type junction. 

A calomel sleeve junction electrode can provide low junction potential while adding a small amount of potassium chloride electrolyte to the sample and thereby reducing its resistance. Some users reduce the concentration of the normally saturated KCl filling solution to 0.1 M KCl in order to minimize the junction potential and to decrease stabilization time. This electrode potential is listed in Table 3.5. 

One method of reducing this error is by the use of a high salt buffer. For example, a seawater buffer described in Chapter 4 provides greater accuracy when measuring the pH of seawater. Another method is the use of a fast-flowing low-resistance junction such as the sleeve junction. 

Since there is no universal junction which is compatible with or will perform well in all types of samples, one possible solution to difficulties may require the use of another reference electrode with a different type of junction. A general indication of preferred junctions for different types of samples was shown in Table 3.3. Most often, a sleeve junction will provide good performance and should be selected if the disadvantages of the flow rate and maintenance discussed in Chapter 3 are acceptable. Chapter 3 also discusses altering the reference filling solution to make the junction more compatible with the sample. 

The use of a fast-flowing low-resistance jimction, such as the sleeve junction. 

Completely insulate the materials from one another at all junctions exposed to a common fluid. Insulation involves using nonconductive washers, inserts, sleeves, and coatings. 

A junction in a transfer tube is useful when two parts of the tube are fixed to the respective dewars. An example of a transfer tube is shown in Fig. 5.8. Figure 5.9 shows a sleeve coupling. Examples of transfer lines are in ref. [27,28],... 

When specific ion electrodes are employed, an error of less than 1 to 2% of the activity of the ion is desirable. This requires that the potential measurement have an error of less than 0.1 to 0.2 mV the reproducibility of the junction potential becomes a critical factor in the measurement. The sleeve-type junction... 

Rgure 2.3. Schematic cross-section representation of the construction of some typical commercial calomel electrodes A) fiber or porous-ceramic Junction type and (B) ground glass-sleeve type. The electrolyte leak rate of the fiber or porous-ceramic junction type is quite low, typically 1-10 fJ/Ar that for the sleeve type around 100 ft//Ar. 

Fig. 2.8-2 a) Principle of a thermoelement circuit with three materials A, B, and Cu and the cold junction temperature To. The cold junction can be a thermostat (e.g., ice bath) or a correction circuit, b) Measuring probe inserted in a protective sleeve. 

In a stretch pattern, if the crown pattern geometry retains a similar profile to the conventional set-in sleeve pattern, with little change in the crown depth, fiiis impairs the quality of the garment fit. When a crown pattern profile similar to a shirt is dniied in a stretch pattern, the width of the low r sleeve may remain narrow with increased width between the underarm seam junctions. This allows tiie atm to move freely without fabric displacement after movmnmiL... 

Reference electrode A potentiometric half-cell, comprising an inner element, usually calomel or silver-silver chloride, a chamber containing the appropriate filling solution, and a device forming a liquid junction between the filling solution and the sample (e.g., a fritted disk, a ground glass sleeve, or a narrow-bore hole). 

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