6
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. ISA should be added to
both samples and standards in the same ratio. 1 part
ISA to 50 parts standard is the normal dosing.
•
Concentrated samples (>1 M) should be diluted
before measurement. Multiply the final result by the
corresponding dilution factor.
•
For high ionic strength samples, prepare standards
with similar ionic strength by increasing the quantity
of ISA used or use standard addition or titration.
•
Calibration standards and sample solutions should
be at same temperature.
•
The magnetic stirrer may generate heat. Thermally
insulate beaker containing standard or sample from
magnetic stirrer by placing cork or other insulative
sheet between beaker and stirrer plate.
•
Calibration standards and sample solutions should
be stirred at the same rate using identical sized TFE
coated stir bars.
•
Rinse electrode pair with distilled or deionized water
between samples and gently dab dry with soft dis-
posable absorbent toweling. Do not rub electrodes.
•
Presoaking Iodide sensor in a dilute standard will
optimize response. Use concentrations approximately
10
-3
M or less.
•
A scratched, pitted, or tarnished pellet surface can
cause drift, a loss of low level response, or poor repeat-
ability. Optimum response can be restored by remov-
ing the damaged surface with the microabrasive strip
HI 4000-70.
•
Avoid large changes in temperature (thermal shock)
as it may damage the sensor.
•
Gas bubbles may form from solution out-gassing due
to temperature change. Gently tap body of sensor to
dislodge them from membrane surface.
