PASCO Specialty & Mfg. PASCO CI-6735 Benutzerhandbuch
Nitrate Ion Selective Electrode
012–06616A
8
2. Dilute 1 ml of 0.l M standard to 100 ml to prepare a l.0Xl0
-3
M NO
3
-1
solution for measurements in moles
per liter. Use the 1,000 ppm standard for preparing a 100 ppm NO
3
-1
standard by diluting 10 ml of the
1,000 ppm standard to 100 ml. Standards should be prepared fresh daily.
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 tip in the solution. Assure that ScienceWorkshop is operating.
5. Add increments of the l.0Xl0
-3
M or 100 ppm standards as given in Table 2 below.
6. After the reading has stabilized, record the Voltage reading in the Digits Display after each addition.
TABLE 2: Step-wise Calibration for Low Level Nitrate Measurements
Added
Concentration
Step
Pipette
Volume (mL)
M NO
3
-1
ppm NO
3
-1
1
A
0.1
1.0 X 10
-6
0.1
2
A
0.1
2.0 X 10
-6
0.2
3
A
0.2
4.0 X 10
-6
0.4
4
A
0.2
6.0 X 10
-6
0.6
5
A
0.4
9.9 X 10
-6
1.0
6
B
2.0
2.9 X 10
-5
2.9
7
B
2.0
4.8 X 10
-5
4.8
Pipette A = 1 ml graduated pipette
Pipette 8 = 2 ml pipette
Solutions: additions of l.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 voltage reading on the Digits display (linear axis) against the
concentration (log axis) as in Figure 3.
8. Rinse the electrode and blot dry.
9. 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 tip into the solution. After the reading has
stabilized, record the Voltage reading indicated in the Digits Display and determine the concentration
from the low level calibration curve.
10. Prepare a new low level calibration curve daily. Check the calibration curve every two hours by repeating
steps 2 - 7.