affect speed of response). Aging is best detected by calibrating the electrode in, for example, 7 buffer and then
rinsing and placing the electrode in 4.01 buffer. As a rule, if the span if 10% or more in error (a reading of 4.3 or
higher for this example the electrode should be cleaned and/or reconditioned and retested. If reconditioning does
not restore performance the electrode should be replaced.
When reconditioning is required due to electrode aging (see Helpful Operating Techniques, Pg. 18), the following
chemical treatments should be tried. They are presented in the order of the severity of their attack on the pH glass and
may not improve (and in some cases actually further deteriorate) electrode performance.
Immerse the electrode tip in 0.1N HCL for 15 seconds, rinse in tap water and then
immerse tip in 0.1N NaOH for 15 seconds and rinse in tap water. Repeat this
sequence several times and then recheck electrode performance. If performance has
not been restored, try Step 2.
Immerse the tip in a 20Z solution of NH4F.HF (ammonium bifluride) for 2 to 3 minutes,
rinse in tap water and recheck performance. If performance has not been restored, try
Immerse electrode tip in 10X HF for 10 to 15 seconds, rinse well in tap water, quickly
rinse in 5N HC1, rinse well in tap water and recheck performance. If performance has
not been restored, it is time to get another Delta electrode.
When pH readings are made infrequently, for example, several' days or weeks apart, the electrode can be stored simply
by replacing its protective cap. Make certain that the cotton inside the cap is wet (use distilled water), that the cap
pressure relief hole is open and slowly push the cap into position. Then, cover the hole in the cap's side with a piece of
tape. For very long term storage, taping the top of the cap to the electrode's body will provide additional protection
against water loss.