What is a pH indicator electrode?
The electrode that responds to the activity of hydrogen ions in the solution and changes the electrode potential is called a pH indicator electrode or pH measurement electrode. pH indicator electrodes include hydrogen electrodes, antimony electrodes, and glass electrodes, but the most commonly used electrodes are glass electrodes. Glass electrode is a glass rod, as well as by the special composition of the composition of the glass membrane sensitive to hydrogen ions. The glass membrane is generally in the form of a bulb, which is filled with an internal reference solution, inserted into the internal reference electrode (generally silver/silver chloride electrode), sealed with an electrode cap to connect the lead wires, and fitted with a socket, which becomes a pH indicator electrode. A single pH indicator electrode is unable to measure, it must be measured together with the reference electrode.
2,What is a reference electrode?
The electrode that does not respond to the activity of hydrogen ions in solution and has a known and constant electrode potential is called a reference electrode. There are several types of reference electrodes such as mercury sulfite electrode, calomel electrode and silver/silver chloride electrode. The most commonly used are the calomel electrode and the silver/silver chloride electrode. The role of the reference electrode in the measurement cell is to provide and maintain a fixed reference potential, so the requirements of the reference electrode is a stable, reproducible potential, temperature coefficient is small, there is a current through the polarisation potential is small.
3, what is the pH composite electrode?
The combination of pH glass electrode and reference electrode is called pH composite electrode. Shell for the plastic is called plastic shell pH composite electrode. Shell for the glass is called glass pH composite electrode. The biggest advantage of the composite electrode is the combination of two into one, easy to use. pH composite electrode structure mainly consists of electrode bulb, glass support rod, internal reference electrode, internal reference solution, shell, external reference electrode, external reference solution, liquid boundary, electrode cap, electrode wire, socket and other components.
(1) electrode bulb: it is made of lithium glass with hydrogen function melt blown, spherical, film thickness in 0.1 ~ 0.2mm or so, resistance value of "250 megohm (25 ℃).
(2) glass support tube: is to support the electrode bulb glass tube body, made of lead glass with excellent electrical insulation, its expansion coefficient should be consistent with the electrode bulb glass.
(3) Internal reference electrode: silver/silver chloride electrode, the main role is to lead the electrode potential, the potential is required to be stable, the temperature coefficient is small.
(4) within the reference solution: the zero potential of 7pH within the reference solution, is a mixture of neutral phosphate and potassium chloride, glass electrodes and reference electrodes constitute a battery to establish the zero potential of the pH value, mainly depends on the pH value of the reference solution and chloride ion concentration.
(5) Electrode plastic shell: the electrode plastic shell is to support the glass electrode and liquid junction, holding the outer reference solution shell, by the PPS plastic pressure moulding.
(6) external reference electrode: silver / silver chloride electrode, the role is to provide and maintain a fixed reference potential, the requirements of potential stability, good reproducibility, temperature coefficient is small.
(7) External reference solution: 3.3 mol / L of potassium chloride gel electrolyte, not easy to lose, no need to add.
(8) Sand core liquid junction: liquid junction is the connecting part of the structure through the external reference solution and the measured solution, and requires stable permeability.
(9) Electrode wire: low-noise metal shielded wire, the inner core is connected to the inner reference electrode, and the shield is connected to the outer reference electrode.
