Hanna Instruments HI 4010 - Manual (Page 6)

6
Using volumetric pipettes and glassware make dilutions to
bracket the concentration of the samples. Standards with
concentrations < 10
-4 M (1.9 ppm) should be prepared
daily. Standards that are asterisked contain TISAB II and
should be used directly with no additional TISAB II added.
Samples used with these standards should have TISAB II
added. To 50 parts standard or sample add 50 parts TISAB
II (HI 4010-00, HI 4010-05) or to 50 parts standard or
sample add 5 parts of TISAB III concentrate (HI 4010-06).
Note: TISAB is formulated for water sample analysis to
provide samples and standards a constant ionic strength
and pH background that stabilizes the solutions activity
coefficient and permits concentration to be measured di-
rectly. It preferentially complexes various metal ions (i.e.
Aluminum; Al
3+ , Iron; Fe 3+ ) that also complex with fluo-
ride thus permitting a total fluoride measurement. Contact
Hanna Instruments for guidelines with other applications.
VII VII VII VII VII. General Guidelines General Guidelines General Guidelines General Guidelines General Guidelines
•
Calibration standards and sample solutions should
have the same ionic strength. Use the same TISAB (II
or III) for both samples and standards. Always pre-
pare samples and standards with the same ISA to
volume ratio.
•
Calibration standards and sample solutions should
be at same temperature.
•
Thermally insulate beaker with standard or sample
from magnetic stirrer.
•
Calibration standards and sample solutions should
be stirred at the same rate using identical sized TFE
coated stir bars.
•
Rinse electrodes with distilled or deionized water be-
tween samples and gently dab dry with lab wipe or
other soft disposable absorbent toweling. Do not rub
crystal.
•
Presoaking fluoride sensor in a standard near sample
concentrations will activate crystal and optimize re-
sponse.
*