From Big Medical Encyclopedia

GLASS ELECTRODE — the ion-selective electrode intended for definition of hydrogen ion activity, sodium or potassium in aqueous mediums. Electrodes of this type found broad application in various scientific research, during the carrying out a wedge, analyses and in a number of productions since allow to watch dynamics of change of ion activity continuously.

Page e. represent the thin spherical or flat membrane from special grades of glass soldered to an end face of a tube from usual glass, inside the cut is built in an auxiliary electrode, most often chlorine - silver or calomel electrode (see). Depending on tasks produce S. e. various configurations — flowing capillary, needle etc.

One of the main characteristics of S. e. ability to keep electrode function in relation to this ion in the presence of other ions — i.e. specificity (see is. Ion-selective electrodes ). S.'s example e. with highly specific function the modern rn-electrodes allowing to work in a wide interval of pH values (from 0 to 13) practically irrespective of existence in solution of other ions are. The coefficient of specificity at modern pH-electrodes reaches values 10 14 — 10 15 in favor of hydrogen ions in relation to ions of monovalent metals. High specificity is provided with exclusively strong communication of ionizable group of glass with hydrogen ions. S.'s specificity e. for measurement of ion activity of sodium and potassium it is characterized by coefficient of specificity of an electrode to sodium in comparison with potassium (K Na/K ). PRI K Na/K = 1 electrode is equally specific to both ions and cannot be used for definition of concentration of each of them in mix of these ions. At K Na/K > 1 Na-function (a sodium electrode) is more specific to an electrode; at K Na/K < 1 — K-function (a potassium electrode). In the majority of the existing glass electrodes can reach 250 for sodium S. e.; in potassium S. e. this coefficient lower than 0,2.

S.'s lack e. with buffer solution, used in medical practice, difficulty of their sterilization is. S. e are developed., in to-rykh the internal firm contact with a glass electrode is made. These electrodes can be sterilized heating to temperatures exceeding 100 °.

See also Potentiometric titration , Electrodes .

Bibliography: Bates R. Definition of pH, the Theory and practice, the lane with English, page 258, D., 1968.

G. A. Kurella.