PASCO Specialty & Mfg. PASCO Scientific SODIUM ION SELECTIVE ELECTRODE CI-6734 Benutzerhandbuch
012–06615A
Sodium Ion Selective Electrode
9
Electrode drift and slow response could indicate the presence of high interference from the ions listed. Soak the
electrodes in electrode storage solution when this happens to restore proper response. See Measuring Hints
section.
TABLE 3: Levels of Interfering Ions Resulting in a 10% Error at Specified Levels of Sodium
Interference
1.0X10
-4
M
1.0X10
-3
M
1.0X10
-2
M
Li
+1
5X10
-4
M
5X10
-3
M
5X10
-2
M
K
+1
1X10
-2
M
1X10
-1
M
1 M
Rb
+1
3X10
-1
M
3 M
NH
4
+1
3X10
-1
M
3 M
Ag
+1
3X10
-9
M
3X10
-8
M
3X10
-7
M
Tl
+1
5X10
-2
M
5X10
-1
M
Interference
1 ppm
10 ppm
100 ppm
Li
+1
1.5 ppm
15 ppm
150 ppm
K
+1
17 ppm
170 ppm
1,700 ppm
Rb
+1
1.1X10
4
ppm 1.1X10
5
ppm
NH
4
+1
1.8X10
3
ppm 1.8X10
4
ppm
Ag
+1
0.0001 ppm
0.001 ppm
0.01 ppm
Tl
+1
4.5X10
3
ppm 4.5X10
4
ppm
Temperature Influences
Samples and standards should be at the same temperature, since electrode potentials are influenced by changes in
temperature. A l °C difference in temperature results in a 2% error at the l0
-3
M level. Because of solubility equilibria
on which the electrode depends, the absolute potential of the reference electrode changes slowly with temperature.
The slope of the electrode, as indicated by the factor “S” in the Nernst equation, also varies with temperature. Table
4 indicates the variation of theoretical slope with temperature.
Provided that temperature equilibria has occurred, the sodium ion electrodes can be used at temperatures from -5 °
to 70 °C. Room temperature measurements are recommended, since measurements at temperatures markedly
different from room temperature may require equilibrium times up to one hour. The electrode should not be used
at temperatures above 70 °C, since damage to the membrane may result.
TABLE 4: Temperature vs. Values for the Electrode Slope
Temperature ( ºC)
“S”
0
54.20
10
56.18
20
58.16
25
59.16
30
60.15
40
62.13
50
64.11