pH meter - the structure of the composite electrode
⑴ Electrode bulb: It is made of molten lithium glass with hydrogen function and is spherical in shape, with a film thickness of about 0.1-0.2mm and a resistance value of <250 megohms (25°C).
⑵Glass support tube: it is the glass tube body that supports the electrode bulb. It is made of lead glass with excellent electrical insulation, and its expansion coefficient should be consistent with that of the electrode bulb glass.
(3) Internal reference electrode: It is a silver/silver chloride electrode, the main function is to lead out the electrode potential, and its potential is required to be stable and the temperature coefficient is small.
(4) Internal reference solution: The internal reference solution with a zero potential of 7pH is a mixed solution of neutral phosphate and potassium chloride. The glass electrode and the reference electrode form a battery to establish a pH value of zero potential, which mainly depends on the pH of the internal reference solution value and chloride ion concentration.
⑸Electrode molded case: The electrode molded case is a shell that supports the glass electrode and the liquid junction, and holds the external reference solution, and is molded by PPS plastic pressure.
⑹External reference electrode: It is a silver/silver chloride electrode, whose function is to provide and maintain a fixed reference potential, which requires stable potential, good reproducibility, and small temperature coefficient.
⑺External reference solution: 3.3mol/L potassium chloride gel electrolyte, not easy to lose, no need to add.
⑻Sand core liquid junction: The liquid junction is the connecting part that connects the external reference solution and the measured solution, and requires stable penetration.
⑼ Electrode wire: It is a low-noise metal shielded wire, the inner core is connected to the inner reference electrode, and the shielding layer is connected to the outer reference electrode.
