Hanna Instruments HI 4012 - Manual (Page 6)

6
VII VII VII VII VII. General Guidelines General Guidelines General Guidelines General Guidelines General Guidelines
•
Use of a hood and protective clothings is advised
when handling lead solutions.
•
Concentrated samples (>0.10 M) should be diluted
before measurement. Multiply the final result by the
corresponding dilution factor.
•
Calibration standards and sample solutions should
have the same ionic strength. ISA and Methanol/
Formalin should be added to both samples and stan-
dards in the same ratio. 2 parts ISA to 50 parts stan-
dard (or sample)/50 parts Methanol/Formalin is the
normal dosing. Note: no correction for dilution factor is
required for this because standards and samples are
treated in the same way.
•
For high ionic strength samples, use standard addi-
tion or titration methods.
•
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 lead sensor in a dilute standard will opti-
mize response. Use concentrations approximately
10
-3 M or less with Methanol/Formalim and ISA added.
•
A scratched, pitted, or oxidized pellet surface can cause
drift, a loss of low level response, or poor repeatability.
Optimum response can be restored by removing the
damaged surface with the microabrasive strip HI 4000-
70. Use gloves to protect skin.
•
Avoid large changes in temperature (thermal shock)
as it may damage the sensor.