Hanna Instruments HI 4105 - Manual (Page 7)

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XII. XII. XII. XII. XII. Sample Handling Sample Handling Sample Handling Sample Handling Sample Handling
•
For optimum results, allow samples and standards
and the HI 4105 electrode to reach the same tem-
perature.
•
As CO
2
is volatile, measure samples immediately af-
ter collection.
•
If sample must be stored: Completely fill collection
bottle with dilute samples and tightly cap container
to prevent carbon dioxide loss or contamination from
other sources.
•
If sample must be stored: For acetic samples. add
sodium hydroxide (10N) to raise pH to 8-9 for stor-
age. Tightly close collection bottle.
•
If sample must be stored: keep sample at a lower
temperature than it was collected at until time of
measurement.
•
Add Hanna HI 4005-00 ISA just prior to measure-
ment to adjust standards and samples to a pH
between 4.2-5.2 for measurement. ISA must mix
thoroughly with solutions and time allowed to convert
carbonate and bicarbonate species to CO
2
(dissolved).
•
Covering sample and standards after adding ISA will
minimize carbon dioxide loss from the solution.
•
Calibration standards and samples must be the same
ionic strength. The concentration for all dissolved spe-
cies in a sample should not exceed 1M. Samples that
exceed this should be diluted with CO
2
free deion-
ized water. Do not reduce CO
2
below 10 -4 M. Multiply
the final result by the corresponding dilution factor.
X. X. X. X. X. Quick Check of Electrode Slope Quick Check of Electrode Slope Quick Check of Electrode Slope Quick Check of Electrode Slope Quick Check of Electrode Slope
•
Connect BNC (connector) to pH/mV/ISE meter.
•
Place meter in mV mode.
•
Place 100 mL of deionized water into a vessel with
stir bar. Add 10 mL of ISA Hanna HI 4005-00.
•
Place sensor into prepared sample.
•
Add 1 mL of 0.1 M Carbon dioxide standard to
beaker and stir sample. Wait approximately 5 min-
utes. Record the mV value when stable.
•
Add an additional 10 mL of standard to the solution.
Record the mV when reading has stabilized (approxi-
mately 5 minutes). This value should be greater
than the previous noted (more positive).
•
Determine the difference between the two mV values.
An acceptable value for this slope is 54
±4 mV at
ambient temperatures between 20 and 25 °C.
Note: HI 4005-03 standard may be used. The additions
must be 10mL and 100mL. The mV difference should
be approximately 47mV.
XI. XI. XI. XI. XI. Corrective action Corrective action Corrective action Corrective action Corrective action
•
Verify standard has been properly added.
•
Verify ISA has been added in the correct ratio to the
standard (1 part ISA to 10 parts sample or standard).
•
Verify that the upper cap has been screwed in all the
way.
•
Verify electrode is connected properly to meter and the
meter is is powered .
•
Verify membrane cap is tightened securely to probe
body.
•
Examine the membrane for discoloration or perfora-
tions or for internal fill solution that might have
leaked through the PTFE membrane. Replace mem-
brane cap if damaged.
If drift is seen:
•
Verify electrode and standards are at same tempera-
ture.
•
Verify electrode has adaquate fill solution.
•
Verify electrode was not left in air for prolonged pe