eutech-instruments chloride epoxy User Manual

Instruction Manual 

 

Chloride Electrode 

 

15

 
The upper limit of detection in pure sodium chloride solutions is 1M. In the presence of other ions, 
the upper limit of detection is above 1.0x10

-1

M chloride, but two factors influence this upper limit. 

Both the possibility of a liquid junction potential developing at the reference electrode and the salt 
extraction effect influence this upper limit. Some salts may extract into the electrode membrane at 
high salt concentrations, causing deviation from the theoretical response.  Either dilute samples 
between 1M and 1.0x10

-1

M or calibrate the electrode at 4 or 5 intermediate points. 

 
The lower limit of detection is influenced by the slight water solubility of the electrode pellet.  
Refer to Figure 1 for a comparison of the theoretical response to the actual response at low levels of 
chloride.  Chloride measurements below 10

-4

M CL

-1

 should employ low level procedures. 

 

 
Hydroxide ion interferes with measurements of low levels of chloride although the electrode can be 
used over a reasonable pH range. Table 3 should be used to determine the minimum pH at which 
low level chloride measurements can be made without more than a 10% error due to hydroxide ion 
interference. 
 

 
A chloride ion electrode will last for six months in normal laboratory use. On-line measurements 
might shorten operational lifetime to several months. In time, the response time will increase and 
the calibration slope will decrease to the point calibration is difficult and electrode replacement is 
required. 
 

 
The electrode may be stored for short periods of time in 1.0x10

-2

M chloride solution. For longer 

storage (longer than two weeks), rinse and dry the sensing pellet and cover the membrane tip with 
any protective cap shipped with the electrode. The reference portion of the combination electrode 
(or the outer chamber of the reference electrode) should be drained of filling solution, if refillable, 
and the rubber insert placed over the filling hole.