eutech-instruments ammonia gas Manuale Utente

Instruction Manual 

 

Ammonia Gas-sensing Electrode

 

 

10

 
Metal complexes are formed with ammonia and a number of metal ions. Complexes of mercury, 
copper, gold, silver, nickel, zinc, cobalt, and cadmium are removed in the form of hydroxide 
complexes or precipitates in basic solution. When ammonia concentration is below 10-

3

M and 

hydroxide is present at the 10-

1

M level, the only appreciable complex formed will be between 

mercury and ammonia. Since the total ammonia level of a sample will be measured if the mercury is 
preferentially bound to another species, addition of iodide is recommended for this purpose. Use of 
the recommended ISA (10M NaOH solution) inhibits the formation of metal complexes in the 
sample, since it contains a high concentration of hydroxide ions. 
 

 
Table 4 gives the variation of theoretical response with temperature. The electrode response will 
shift and change slope with change in temperature. Standards and samples should be at the same 
temperature. A 2% error results with a 1oC temperature change for a 10-

3

M solution. Gases are 

expelled from a solution at a faster rate as the temperature increases. 
 
    TABLE 4: Temperature vs. Values for Electrode Slope 
 
                Temp.(oC)        "S"  
                    0                54.20 
                    5                55.20 
                   10                56.18 
                   15                57.17 
                   20                58.16 
                   25                59.16 
                   30                60.15 
                   35                61.14 
                   40                62.13 

 
Plotting the electrode mV potential against the ammonia concentration on semi-logarithmic paper 
results in a straight line with a slope of about 56 mV per decade.  (See Figure 1.) 
 
For ammonia concentrations above 4X10-

6

M (0.07 ppm NH3 or 0.06 ppm N), the electrode exhibits 

good time response  (95% of total mV reading in one minute or less). Response times are longer 
below this value and ammonia loss to air may become a source of error. Figure 2 indicates the time 
response of ammonia electrode to changes in the ammonia concentration.