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

Sodium Electrode Instruction Manual
6
9. After rinsing the electrodes and blotting dry, place the electrode tips in the solution and
wait for the reading to stabilize. Read the concentration directly from the meter display.
10. The calibration should be checked every two hours. Assuming no change in ambient
temperature, place the electrode tips in the first sodium standard. After the reading has
stabilized, compare it to the original reading recorded in Step 4 above. A reading
difference by more than 0.5 mV or a change in the ambient temperature will necessitate the
repetition of Steps 2-8 (9) above. The meter should be recalibrated daily.
Low Level Sodium Determination (using a pH/mV meter)
This procedure is recommended for solutions with ionic strength less than 1.0X10-
2
M and a sodium
concentration less than 1X10-
5
M or 1 ppm. If the solution is high in ionic strength, but low in
sodium, use the same procedure, but prepare a calibration solution with a composition similar to the
sample. Use plastic lab-ware for low sodium measurements.
1. Using 20 ml of standard ISA, dilute to 100 ml with distilled water.
2.
Dilute 20 ml of the outer chamber filling solution to 100 ml with distilled water and fill
the reference electrode if using a double junction reference electrode.
3.
Dilute 1 ml of the 0.1M standard to 100 ml to prepare a 1.0X10-
3
M standard solution for
measurements in moles per liter. Dilute 10 ml of the 1,000 ppm standard solution to 100
ml to prepare a 100 ppm standard solution for measurements in ppm. Add 1 ml of low
level ISA to each 100 ml of standard. Standards should be prepared fresh daily.
4.
Using a 150 ml plastic beaker, add 100 ml of distilled water and 1 ml of low level ISA.
Add NH
4
OH, if necessary, to adjust the pH above 9. Place the beaker on the magnetic
stirrer and begin stirring at a constant rate.
5. Place the electrode tips in the solution. Assure that the meter is in the mV mode.
6.
Add increments of the 1.0X10-
3
M or 100 ppm standard as given in Table 2 below.
7.
After the reading has stabilized, record the mV reading after each addition.
TABLE 2: Step-wise Calibration for Low Level Sodium Measurements
Added Concentration
Step Pipet Volume (ml) M ppm
1 A 0.1 1.0X10-
6
0.10
2 A 0.1 2.0X10-
6
0.20
3 A 0.2 4.0X10-
6
0.40
4 A 0.2 6.0X10-
6
0.60
5 A 0.4 9.9X10-
6
0.99
6 B 2.0 2.9X10-
5
2.91
7 B 2.0 4.8X10-
5
4.76
Pipet A = 1 ml graduated pipet
Pipet B = 2 ml pipet
Solutions: additions of 1.0X10
-3
M or 100 ppm standard to 100 ml of distilled water and 1 ml
of low level ISA.