A pH electrode that is properly manufactured
and kept clean will retain its measuring integrity for quite a long time.
The most common cause for pH measurement
inaccuracies is an unclean or improperly cleaned electrode. This is very
important to note because, during calibration, the instrument assumes that the
electrode is clean and that the standardization curve created during the
calibration process will remain a valid reference until the next calibration.
pH meters on the market today will allow an
offset of approximately ±60 mV. The deviation from 0 mV is not unusual, in
fact it represents the true characteristics of the pH electrode. The deviation
from 0 mV becomes a problem if it is the result of calibrating a dirty
HANNA®' HI 221
& HI 223 compare the characteristics of the pH electrode from one
calibration to the next. In case of large variances in the electrode condition
that can only be the result of a soiled sensor, these meters alert the user
that the electrode needs to be properly cleaned prior to calibration and
HI 221 is supplied with HI 1131P refillable pH electrode (glass-body, BNC
& Pin with 1m cable), HI 7669/2W stainless steel temperature probe, HI
76404 electrode holder, pH 4 and pH 7 buffer sachets, electrode refilling
solution, 12 Vdc power adapter and instructions.