Thermo Fisher Scientific Ion Selective Electrodes Calcium - Manual (Page 8)

Calcium Electrode Instruction Manual
8
7. The calibration should be checked every two hours. Assuming no change in ambient
temperature, place the electrode tips in the mid-range standard. After the reading has
stabilized, compare it to the original reading recorded in Step 3 above. A reading differing
by more than 0.5 mV or a change in the ambient temperature will necessitate the repetition
of Steps 2-5 above. A new calibration curve should be prepared daily.
Direct Measurement of Calcium (using an ion meter)
1. By serial dilution of the 0.1M, 1,000 ppm, or 100 ppm calcium standard, prepare two
calcium standards whose concentration is near the expected sample concentration.
Measure out 100 ml of each standard into individual 150 ml beakers and add 2 ml of ISA
to each.
2.
Place the more dilute solution on the magnetic stirrer and begin stirring at a constant rate.
Assure that the meter is in the concentration mode. Lower the electrode tips into the
solution.
3.
Adjust the meter to the concentration of the calcium standard and fix the value in the
memory according to the meter manufacturer's instructions after stabilization of the
reading. Rinse the electrode tips with distilled water and blot dry.
4.
Place the more concentrated solution on the magnetic stirrer and begin stirring at a
constant rate. Lower the electrode tips into the solution.
5.
Adjust the meter to the concentration of the calcium standard and fix the value in the
memory according to the meter manufacturer's instructions after stabilization of the
reading.
6.
For low level measurements, place the rinsed, dried electrodes into a solution containing
100 ml of distilled water and 2 ml of ISA. After stabilization, fix the blank value in the
meter according to the meter manufacturer's instructions.
7.
Place 100 ml of the sample and 2 ml of ISA in a 150 ml beaker. Place the beaker on the
magnetic stirrer and begin stirring.
8.
Immerse the electrode tips in the solution and wait for the reading to stabilize. Read the
concentration directly from the meter display.
9.
The calibration should be checked every two hours. Assuming no change in ambient
temperature, place the electrode tips in the first calcium standard. After the reading has
stabilized, compare it to the original reading in Step 3 above. A reading differing by more
than 0.5 mV or a change in ambient temperature will necessitate the repetition of Steps 2-6
above. The meter should be re-calibrated daily.
Low Level Calcium Determination (using a pH/mV meter)
This procedure is recommended for solutions with ionic strengths less than 1.0X10
-2
M. If the
solution is high in ionic strength, but low in calcium, use the same procedure, but prepare a
calibration solution with a composition similar to the sample.