Ag/AgCl reference electrode (CS901)
It consists of a Teflon cap with a AgCl coated Ag wire, a glass tubing, and a porous Teflon tip sealed into the glass tubing.
Porous Teflon tip has the following advantages: slow solution leak and more durability due to its perfect chemical inertness. However, you should still take good care of the electrode. The most critical issue is that the electrode should always be dipped in KCl solutions when it is not in use. If you leave it in air by accident, the solution inside the pores will dry out causing high resistance (you will see noise increase or even potential out of control if the tip is seriously dried out). The only way to restore it is to fill it with solution and slowly push the solution through the porous Teflon tip.
The reference electrode compartment (the glass tubing) is filled with 3.5M KCl. You can fill with other concentration KCl. The potential of the reference electrode versus the Standard Hydrogen Electrode (0.0V) can be calculated from the activity (not concentration) of Cl ion.
Before you use the reference electrode, you need to remove the cap at the end of the electrode. Tap the tubing and make sure no air bubble is trapped in the lower portion of the tubing. The electrode should be dipped into 1M KCl solution immediately and left overnight before use.
The solution in the compartment is refillable. To do that, carefully unplug the Teflon cap by holding the glass tube with your left hand and using your right thumb to push the edge of the white cap towards the right. Do not pull on the cap and tube directly. It may cause glass tubing to break. Next, use a syringe to refill both the glass tubing and the white Teflon cap. The solution level should be full. Tap the tubing and make sure that no air bubble is trapped in the bottom of the tubing. Slowly insert the glass tubing into the Teflon cap with Ag wire. Please insert very slowly. You will see solution comes out through the tip. It is normal. If you insert too fast, it will generate too much pressure and may cause the porous Teflon tip to be popped out or damaged. After the glass tubing is all the way in the cap, let it sit for a while so that the pressure inside the tubing will be released and no solution will further leak.