Thermo Fisher Scientific Ion Selective Electrodes Nitrate User Manual
Page 9
Instruction Manual
Nitrate Ion Electrode
7
3.
Add 1 ml of the low level ISA to a 100 ml volumetric flask and fill to the mark with distilled
water. Pour this solution into a 150 ml beaker and place the beaker on the magnetic stirrer.
Begin stirring at a constant rate.
4.
Place the electrode tips in the solution. Assure that the meter is in the mV mode.
5.
Add increments of the 1.0X10
-3
M or 100 ppm standards as given in Table 2 below.
6.
After the reading has stabilized, record the mV reading after each addition.
TABLE
2: Step-wise Calibration for Low Level Nitrate Measurements
Added Concentration
Step Pipet Volume (ml) M NO
3
-1
ppm NO
3
-1
1 A 0.1 1.0X10
-6
0.1
2 A 0.1 2.0X10
-6
0.2
3 A 0.2 4.0X10
-6
0.4
4 A 0.2 6.0X10
-
0.6
5 A 0.4 9.9X10
-6
1.0
6 B
2.0 2.9X10
-5
2.9
7 B
2.0 4.8X10
-5
4.8
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 ISA as prepared in Step 3
above.
7. On semi-logarithmic graph paper, plot the millivolt reading (linear axis) against the
concentration (log axis) as in Figure 1.
8. Rinse the electrodes and blot dry. Measure out 100 ml of the sample into a 150 ml beaker, add 1
ml of low level ISA. Place the beaker on the magnetic stirrer and begin stirring. Lower the
electrode tips into the solution. After the reading has stabilized, record the mV reading and
determine the concentration from the low level calibration curve.
9. Prepare a new low level calibration curve daily. Check the calibration curve every two hours
by repeating Steps 2-7.
Low Level Nitrate Determination (using an ion meter)
Follow the procedure given for normal nitrate determinations using an ion meter and the blank
correction procedure.
ELECTRODE CHARACTERISTICS
Reproducibility
Electrode measurements reproducible to ±2% can be obtained if the electrode is calibrated every hour.
Factors such as temperature fluctuations, drift, and noise limit reproducibility. Reproducibility is
independent of concentration within the electrode's operating range.