Thermo Fisher Scientific Ion Selective Electrodes Lead - Manual (Page 11)

Instruction Manual Lead Electrode
9
reading has stabilized, record the mV reading and determine the concentration from the
low level calibration curve. Prepare a new low level calibration curve daily. Check the
calibration curve every two hours by repeating Steps 3- 7 above.
Low Level Lead Determination (using an ion meter)
1. Using 20 ml of standard ISA, dilute to 100 ml with distilled water. This low level (1.0M
NaClO
4
) is added at a the rate of 1 ml low level ISA to each 100 ml of solution. The
background ionic strength will be 1.0X10
-2
M.
2.
Follow the steps given in
Direct Measurement of Lead (using an ion meter)
to the end
of Step 8. Use plastic lab-ware to avoid adsorption of lead on the beaker walls.
3.
Add 50 ml of distilled water, 50 ml of methanol-formaldehyde, and 1 ml of low level ISA
to a 150 ml plastic beaker. Place the beaker on the magnetic stirrer and begin stirring at a
constant rate. Lower the electrode tips into the solution. When the reading has stabilized,
fix the blank value in the meter according to the meter manufacturer's instructions.
4.
Place 50 ml of the sample, 50 ml of methanol- formaldehyde solution, and 1 ml of low
level ISA in a 150 ml plastic beaker. Place the beaker on the magnetic stirrer and begin
stirring at a constant rate. Lower the electrode tips into the solution. When the reading has
stabilized, read the sample concentration directly from the meter display.
5.
The calibration should be checked every two hours. Assuming no change in ambient
temperature, immerse the electrode tips in the more dilute standard. After the reading has
stabilized, compare it to the original reading recorded in Step 3 above. If the reading
differs by more than
±0.5 units, or the temperature has changed from ambient, recalibrate
the electrode.