Milwaukee Instruments, MA911B/2, Lab Grade Double Junction pH Electrode with Extended CableThe MA911B/2 probe is lab grade, gel-filled pH probe for use with Milwaukee Monitors and Controllers.Features:The double junction junction design reduces the risk of clogging.The sperical glass tip provide the largest possible surface area for faster results.The resin body is tough to withstand accidental knocks and also protects the glass sensing bulb.Offers a 6.6 feet cable for increased flexibility in measuring.pH meters usually start performing poorly because of problems with the probe. The two parts of the pH probe that cause problems are the glass sensing bulb and the reference junction.The glass bulb loses sensitivity with use and will eventually fail. This is true of all pH probes.The reference junction is a small hole that allows the meter to compare the sample to a reference. The reading is generated based on the electrical difference between the sample and reference. If the junction hole gets clogged, the pH probe will no longer function. The pH probe needs to be kept hydrated. Long periods of dry storage will damage the sensitivity of the probe. Allowing the probe to dry out may also result in the junction hole getting clogged.Storing in pH probe storage solution or pH calibration buffers will help address both these issues. Do not store in tap water and DI water. This will damage the sensitivity of the probe.The best way to store the probe is with the probe's cap filled with storage solution or calibiration buffer and the cap tightened to prevent leakage. It is also recommended that to store the electrode upright to further reduce the potential for leakage.Residue from the sample can impact the sensitivity of the sensing bulb and block the junction. This is especially true if the sample has a lot of organic material.The pH sensing bulbs become less sensitive over time so make sure that you are calibrating regularly to keep your PRO pH meter accurate. Also, calibrate after cleaning or a long period of storage.