10
IX.
IX.
IX.
IX.
IX. 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
Use of a hood and protective clothing is strongly advised.
•
Connect sensors to pH/mV/ISE meter
•
Place meter in mV mode.
•
Place 50 mL of deionized water into a beaker with stir
bar and 2 mL of HI 4012-00 ISA. Add 50 mL of the
methanol/Formalin mixture. Add stir bar and place
on magnetic stirrer.
•
Place electrodes into prepared sample.
•
Add 1 mL of the stock standard HI 4012-01 (or .01 M
or .001 M standard by dilution) to the beaker.
Record the mV value when reading has stabilized.
•
Add an additional 10 mL of standard HI 4012-01 (or
same dilute standard) to the solution. Record the mV
when reading has stabilized. This value should be
more positive than the previous noted.
•
Determine the difference between the two mV values.
An acceptable value for this slope is +27 ± 4 mV.
X.
X.
X.
X.
X. Corrective action
Corrective action
Corrective action
Corrective action
Corrective action
•
Verify protective cap has been removed (HI 4012).
•
Verify plastic film has been removed from inner stem
(HI 4112).
•
Verify electrodes are connected properly to meter and
meter is powered.
•
Verify standard has been properly stored. Remake
standards if appropriate.
•
If the sensor slope just misses the suggested slope
window, soaking the sensor in a dilute standard with
the methanol/formalin added may solve the prob-
lem. (
<
10
-3
M standard).
•
A scratched, pitted or oxidized sensing surface can be
polished with HI 4000-70 polishing strip. Cut off
approximately 1 inch of the micro-abrasive strip. Wear
protectice gloves. Wet the frosted side with deionized
water
and place against damaged membrane of the
electrode. Place your gloved thumb against the shiny
backing and slowly rotate back and forth while
