eutech-instruments ammonium epoxy Manuel D’Utilisation

Instruction Manual 

 

Ammonium Electrode 

 

11

                        

Σ = sum of all of the types of ions in the solution. 

In the case of high and constant ionic strength relative to the sensed ion concentration, the activity 
coefficient, 

γ , is constant and the activity, X, is directly proportional to the concentration. 

 
To adjust the background ionic strength to a high and constant value, ionic strength adjuster (ISA) 
is added to samples and standards. The recommended ISA for ammonium is sodium chloride, NaCl.  
Solutions other than this may be used as long as ions that they contain do not interfere with the 
electrode's response to ammonium ions. 
 
The reference electrode must also be considered. When two solutions of different composition are 
brought into contact with one another, liquid junction potentials arise. Millivolt potentials occur 
from the interdiffusion of ions into the two solutions. Electrode charge will be carried unequally 
across the solution boundary resulting in a potential difference between the two solutions, since 
ions diffuse at different rates. When making measurements, it is important to remember that this 
potential be the same when the reference is in the standardizing solution as well as in the sample 
solution or the change in liquid junction potential will appear as an error in the measured electrode 
potential. 
 
The composition of the liquid junction filling solution in the reference electrode is most important. 
The speed with which the positive and negative ions in the filling solution diffuse into the sample 
should be as nearly equal as possible, that is, the filling solution should be equitransferant. No 
junction potential can result if the rate at which positive and negative charge carried into the sample 
is equal. 
 
Strongly acidic (pH = 0-2) and strongly basic (pH = 12-14) solutions are particularly troublesome to 
measure. The high mobility of hydrogen and hydroxide ions in samples make it impossible to mask 
their effect on the junction potential with any concentration of an equitransferant salt. One must 
either calibrate the electrode(s) in the same pH range as the samples or use a known increment 
method for ion measurement. 
 
 
TROUBLESHOOTING 
 

 
The most important principal in troubleshooting is to isolate the components of the system and 
check each in turn.  The components of the system are: 1) Meter,  2) Electrodes,  3) Standard, 4) 
Sample, and  5) Technique. 
 

 
The meter is the easiest component to eliminate as a possible cause of error. Most meter are 
provided with an instrument check-out procedure in the instruction manual and a shorting strap for 
convenience in troubleshooting. Consult the manual for complete instructions and verify that the 
instrument operates as indicated. 
 

 

1. 

Rinse electrode(s) thoroughly with distilled water.