Glass electrodes shielding

Fig. 14. Ultramicio glass electrode according to Sanz (S3). 1, electrode housing (polymethyl metacrylate) 2, glass capillary 3, exchangeable polyethylene capillary tip 4, overflow 5, connection to vacuum pump 0, female cone for connection with a syringe 7, electrolyte solution 8, chlorinated silver spiral 9, shielded cable to compensator 10, filling hole for electrolyte solution 11 and 12, in- and outlet for water from thermostat 13, elastic, high-resistance packing,...

Why is shielding vital in the design of glass electrodes that have an internal resistance of 10 ohms or more. ... 

For titration of halides the solution is best buffered to about pH 5. The indicator electrode is a piece of silver wire of about 1 mm in diameter and about 3 cm long which has been curled into an open spiral the reference electrode may be a mercury-mercurous sulphate half-cell with a potassium sulphate bridge. An alternative reference electrode for use in titration of halides, and one which works well in practice and is convenient to use, is the glass electrode if a glass electrode is used in this way, however, the potentiometer must have a high-impedance, shielded input socket. The following practical details are suitable for halide titrations ... 

For a pair of electrodes we recommend one calomel electrode (slit-junction type) and one glass electrode. The latter should be purchased with a coaxially shielded lead which avoids 1 capacity effects. The leads on each electrode should be about one metre long. The glass, electrode should be of the common kind which i unattacked by acid. The working life of such an. electrode may turn out to be about three months. ... 

Solid electrodes in unstirred solution. The most useful solid electrodes are platinum, gold, vitreous carbon, and carbon paste. The preferred configuration for theoretical work is a flat planar surface sealed in glass with epoxy or snugly fitted into a Teflon shroud. The electrodes ordinarily are unshielded, although shielded designs have been described.94... 

Figure 6.14 Four-compartment cell for controlled-potential electrolysis and coulo-metric titrations. Two central bridge compartments can be emptied to sample compartment by application of nitrogen pressure and refilled by vacuum 1, polyethylene top 2, lock ring 3, combination glass-calomel electrode 4, N2 inlet tube 5, N2 outlet tube 6, Pt gauze electrode 7, cell rinse assembly 8, polyethylene spray shield 9, 0.1 M KC1 in 3% agar gel 10, Ag anode.

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