eutech-instruments ammonium epoxy User Manual

Instruction Manual 

 

Ammonium Electrode 

 

9

 
Plotting the electrode mV potential against the ammonium concentration on semi-logarithmic paper 
results in a straight line with a slope of about 56 mV per decade.  Refer to Figure 1. 
 
The time needed to reach 99% of the stable electrode potential reading, the electrode response time, 
varies from one minute or less for ammonium concentration above 1.0X10-

5

M to several minutes 

near the detection limit.  Refer to Figure 2. 
   

 

 
The ammonium ion electrode may be stored in 1.0X10-

2

M ammonium standard for short periods of 

time. For storage over 3 weeks, rinse and dry the ammonium membrane electrode and cover the tip 
with any protective cap shipped with the electrode(s). 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. 
 

 
The upper limit of detection is 1M in pure ammonium chloride solutions. The upper limit of 
detection is above 1.0X10-

1

M when other ions are present, but the possibility of a liquid junction 

potential developing at the reference electrode and the "salt extraction effect" are two limiting 
factors. Some salts may be extracted into the electrode membrane at high salt concentrations 
causing deviation from theoretical response. Calibrate the electrode at four or five intermediate 
points, or dilute the sample, to measure samples between 1.0X10-

1

M and 1M. 

 
The slight water solubility of the ion exchanger in the sensing module, which causes deviation from 
theoretical response, determines the lower limit of detection.  The theoretical response at low levels 
of ammonium chloride compared to actual response is shown in Figure 1. A low level measurement 
is recommended if ammonium measurements are made below 1.0X10-

5

M (0.18 ppm as 

ammonium).