8
Fluoride Ion Selective Electrode User Guide
Measuring Hints
•
Add 50 mL of TISAB II (Low-level TISAB or TISAB IV) to
every 50 mL of standard or sample. Add 10 mL of TISAB III
to every 90 mL standard or sample. Once TISAB II (Low-
level TISAB or TISAB IV) or TISAB III is selected, it should be
added to all samples and standards so the dilution ratio of
TISAB to solution remains the same.
•
Stir all standards and samples at a uniform rate.
• Always
use fresh standards for calibration.
• Always
rinse the electrode with deionized water between
measurements and shake the electrode to remove the
water and prevent sample carryover. Do not wipe or rub
the electrode sensing element.
•
Allow all standards and samples to come to the same
temperature for precise measurements.
•
Place a piece of insulating material, such as Styrofoam or
cardboard, between the magnetic stirrer and beaker to prevent
measurement errors from the transfer of heat to the sample.
•
Verify the electrode calibration every two hours by placing
the electrode in a fresh aliquot of the least concentrated
standard used for calibration. If using more than 2
standards, use a mid-level standard. If the value has
changed by more than 2%, recalibrate the electrode.
•
After immersing the electrode in a solution, check the
electrode sensing surface for air bubbles and remove air
bubbles by reimmersing the electrode in the solution.
•
For high ionic strength samples, prepare standards with
a background composition similar to the sample or use
manual known addition procedure or a Dual Star meter.
•
Adjust highly acidic or highly basic solutions to pH 5 - 6
before adding TISAB.
•
Remove the fi lling hole cover during measurements to
ensure a uniform fl ow of fi lling solution.
•
If the electrode is used in dirty or viscous samples or the
electrode response becomes sluggish, empty the electrode
completely, hold the junction open and fl ush the junction
with deionized water. Empty any water from the electrode
and refi ll it with fresh fi lling solution. Press down on the
electrode cap to let a few drops of the fi lling solution fl ow
out of the electrode and then replenish any lost solution.
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