What is a ph meter composite electrode and how to use it
An electrode that combines a pH glass electrode and a reference electrode is called a pH composite electrode. The case with plastic shell is called plastic shell pH composite electrode. The one with glass shell is called glass pH composite electrode. The biggest advantage of the composite electrode is that it combines two into one and is easy to use. The structure of the pH composite electrode is mainly composed of electrode bulbs, glass support rods, internal reference electrodes, internal reference solutions, shells, external reference electrodes, external reference solutions, liquid junctions, electrode caps, electrode wires, sockets, etc.
1. 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).
2. Glass support tube: it is the glass tube that supports the electrode bulb. It is made of lead glass with excellent electrical insulation. Its expansion coefficient should be consistent with that of the electrode bulb glass.
3. Internal reference electrode: silver/silver chloride electrode, the main function is to lead out the electrode potential, which requires stable potential and small temperature coefficient.
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 the pH value of the zero potential, which mainly depends on the internal reference solution. pH value and chloride ion concentration.
5. Electrode molded case: The electrode molded case is a shell that supports the glass electrode and the liquid junction, and holds the external reference solution. It is molded by PPS plastic pressure.
6. External reference electrode: silver/silver chloride electrode, the function is to provide and maintain a fixed reference potential, which requires stable potential, good reproducibility and small temperature coefficient.
7. External reference solution: 3.3mol/L potassium chloride gel electrolyte, not easy to lose, no need to add.
8. Sand core liquid junction: The liquid junction is the connecting part that connects the external reference solution and the measured solution, and requires stable penetration.
9. Electrode wire: It is a low-noise metal shielding wire, the inner core is connected to the inner reference electrode, and the shielding layer is connected to the outer reference electrode.
How to use the composite electrode of the ph meter
1. There should be no air bubbles at the front of the bulb, if there are air bubbles, they should be thrown away with force.
2. After the electrode is taken out of the soaking bottle, it should be shaken in deionized water and dried. Do not wipe the bulb with a paper towel, otherwise the time for potential stabilization will be prolonged due to the electrostatic induction of charge transfer to the glass membrane. A better method is to use The solution to be measured rinses the electrodes.
3. After the pH composite electrode is inserted into the solution to be tested, it should be stirred and shaken for a few times and then placed statically, which will speed up the response of the electrode. Especially when using a plastic shell pH composite electrode, the stirring and shaking is more severe, because there will be a small cavity between the bulb and the plastic shell, and after the electrode is immersed in the solution, sometimes the gas in the cavity will produce bubbles if it is too late to get rid of it, making the ball Bubbles or liquid junctions are in poor contact with the solution, so vigorous stirring and shaking is necessary to remove air bubbles.
4. After testing in a viscous sample, the electrode must be rinsed repeatedly with deionized water to remove the sample adhered to the glass membrane. Sometimes it is necessary to wash the sample with other solutions first, then wash with water to remove the solvent, and then immerse in the soaking solution for activation.
5. Avoid contact with strong acid and alkali or corrosive solutions. If you test such solutions, you should minimize the immersion time and wash them carefully after use.
6. Avoid using it in dehydrating media such as absolute ethanol and concentrated sulfuric acid, which will damage the hydration gel layer on the surface of the bulb.
7. The shell material of the plastic shell pH composite electrode is PPS. If the electrode shell medium is damaged, the pH composite electrode with a glass shell should be used instead.
