Thermo Fisher Scientific Ion Selective Electrodes Copper - Manual (Page 13)

Instruction Manual Copper Electrode
13
4. Lower the electrode tip(s) into the solution. When
reading has stabilized, fix the blank value in the
meter according to the meter manufacturer's
instructions.
5. Continue with Steps 8-10 in Direct Measurement of
Cupric Ion (using an ion meter) , remembering to use the
low level ISA described in Step 1 above.
Titration
A very accurate determination of total cupric ion concentration.
This method makes use of the electrode as an endpoint detector
when EDTA is used as a titrant.
Titration of Cupric Ion
The method outlined in this section makes use of the cupric ion
electrode as a highly sensitive endpoint detector for cupric-
containing samples. The titrant used is EDTA.
EDTA complexes cupric as well as other cations. The sample pH
can be adjusted to a low pH by adding HNO
3
to eliminate unwanted
ion complexes. Masking agents may be added in some cases.
1. Prepare the stock EDTA titrant as given in the section
Required Solutions . Dilute the EDTA to 10 to 20 times
as concentrated as the suspected sample concentration.
The sample should contain at least 1.0X10
-3
M cupric ion
for a good detection of the end point.
2. Fill a 50 ml buret with the EDTA solution. Pipette 100
ml of the sample into a 150 ml beaker, place the beaker
on the magnetic stirrer and begin stirring at a
constant rate. Adjust the sample to a low pH by adding
HNO
3
.
3. Position the buret tip in the beaker, slightly above
the liquid level in the beaker and slightly off center.
Position the electrode tip(s) in the solution about
halfway between the center of the beaker and the beaker
wall.
4. Begin adding the EDTA in 0.5 ml to 1.0 ml increment
followed by smaller increments down to about 0.1 ml to
0.2 ml increments as the potential change increases.
Record the mV potential after each addition. Continue
the additions several milliliters past the endpoint
until little change is noted in the mV reading even
when adding 0.5-1.0 ml increments.