Myron L ARH1 - Manual (Page 10)

Samples containing chlorine, sulfur, or ammonia can "poison" any pH
electrode. If it is necessary to measure the pH of any such sample,
thoroughly rinse the pH sensor well with clean water immediately after
taking the measurement. Any sample element which will reduce (add an
electron to) silver, such as cyanide, will attack the reference electrode.
Replacement pH sensors are available only from the Myron L Company or
our authorized distributors.
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Sensor
Body
pH Sensor
Top View pH Glass
Electrode
R e f e r e n c e
Junction
under Glass
pH Bulb