Thermo Fisher Scientific Ion Selective Electrodes Copper - Manual (Page 15)

Instruction Manual Copper Electrode
15
Interferences
A surface layer of silver metal may be formed by strongly
reducing solutions. A layer of silver salt may be deposited on
the membrane if high levels of ions forming very insoluble salts
are present in the sample. Proper performance can be restored by
polishing. See the section entitled Electrode Response for
proper polishing procedure.
The cupric ion electrodes do not respond to anions or most
cations. The electrode membrane is poisoned by solutions
containing mercury and silver. These ions must be absent from the
solution.
If the level of ferric ion is greater then one-tenth the level of
cupric ion in the sample, the measurement will be affected.
Sodium fluoride added to the sample will eliminate ferric ion.
Occasionally, chloride and bromide ions interfere with the
electrode's operation. The level of chloride or bromide ion
relative to the level of cupric ion in the sample is the
determining factor for interference. Interference will occur if
the concentrations are outside the following limits (mole/liter).
(Cu
+2
)(Cl
-1
)
2
> 1.6X10
-6
(Cu +2 )(Br -1 ) 2 > 1.3X10 -12
Figure 4 indicates the regions in which cupric ion and chloride
or bromide ion levels are high enough to cause electrode
interference.
Precipitation and Complexation
Sulfide, phosphate, hydroxide, and other ions precipitate
insoluble cupric salts. The level of cupric ion, the level of