Checking The Electrode Inner Body - EUTECH INSTRUMENTS CARBON DIOXIDE GAS Instruction Manual

Instruction Manual
"Incorrect Answer"
(but calibration
curve is good)

Checking the Electrode Inner Body

If the electrode slope is found to be low during operation, the following solutions will be necessary
to check the inner body:
- pH 4 Buffer (0.1M NaCl added)
Add 2.9 grams of reagent-grade NaCl to 500 ml of pH 4 buffer. Dissolve the solid. The solution
may be stored for repeated use.
- pH 7 Buffer (0.1M NaCl added)
Add 2.9 grams of reagent-grade NaCl to 500 ml of pH 7 buffer. Dissolve the solid. The solution
may be stored for repeated use.
Disassemble the carbon dioxide electrode. If the electrode is dry, soak the glass tip of the inner
body in Eutech Carbon Dioxide Electrode Filling Solution, Code No. EC-ISA-CO1 for two hours.
Rinse the electrode thoroughly with distilled water. Put 100 ml of pH 7 buffer (0.1M NaCl added)
in a 150 ml beaker. Place the beaker on the magnetic stirrer, and begin stirring. Immerse the tip of
the inner body in the solution so that the reference element is covered. Make sure that the meter is
in the mV mode. Record the meter reading when stable.
Rinse the inner body thoroughly in distilled water. Put 100 ml of pH 4 buffer (0.1M NaCl added) in
a 150 ml beaker, place the beaker on the magnetic stirrer, and begin stirring. Immerse the tip of the
inner body in the solution so that the reference element is covered. Observe the change in the meter
reading carefully. In less than 30 seconds after immersion, the reading should change 100 mV. The
meter reading should stabilize in 3-4 minutes, with a difference greater than 150 mV if the inner
body sensing elements are operating properly.
incorrect scaling
of semi-log paper
incorrect sign
incorrect standards
wrong units used
buffer added to
standards and not
samples
sample carryover
19
Carbon Dioxide Electrode
plot millivolts on the linear
axis. On the log axis, be sure
concentration numbers within
each decade are increasing
with increasing concentration
be sure to note sign of millivolt
value correctly
prepare fresh standards
apply correct conversion factor:
-3
10 M = 44 ppm as
CO = 100 ppm as CaCO
2
add same standards
proportions of
buffer to standards and samples
rinse electrodes thoroughly
between samples
3