Recent Advances in Ion-Selective Membrane Electrodes for In Situ Environmental Water Analysis

SYRINGES 
ELECTRONICS
SENSORS
9

b) NITRATE DETECTION 
E
M
F
/
m
V
-8
-6
-5
-4
-3
-7
-
log c
NO
3
600 mM NaCl
1 mM NaCl
50 mV
AgCl
Ag
Ag + 
-
Cl
+
Na
E
app
SAMPLE 
MEMBRANE
RESERVOIR
CE/RE
WE
-
Cl
+
Na
-
Cl
AgCl
Ag + 
-
Cl
Ag
MEMBRANE
+
H
+
Na
+
Na
+
H
-
Cl
-
Cl
-
Cl
-
Cl
SAMPLE
HCl
c) ACIDIFICATION
+
H
+
Na
+
Na
+
H
Figure 6
600 mM NaCl
1 mM NaCl + pH=5.5
50 mV
d) NITRITE DETECTION 
-8
-6
-5
-4
-3
-7
-
log c
NO
2
a) DESALINATION
E
M
F
/
m
V

34 
Table 1. Typical concentrations found for important ions in fresh waters and seawater. Information was 
collected from the following references: [16, 60-67] 
Ion 
Levels 
Freshwater 
Seawater 
pH 
(6.5 ̶ 8.5) 
(7.5 ̶ 8.4) 
Ca
2+
 
(0.05 ̶ 2) mM 
(0.01-10) mM 
Mg
2+
 
0.1 ̶ 25 mM 
0.3 ̶ 60 mM 
NH
4
+
 
(0.1 ̶ 400) µM 
> 1 µM 
NO
3
-
 
0.01 ̶ 20 µM 
0.01 ̶ 100 µM 
NO
2
-
 
0.001 ̶ 5 µM 
0.001 ̶ 10 µM 
Carbonate
a
 
0.1 ̶ 2 mM 
0.1 ̶ 5 mM 
phosphate
b
 
0.002 ̶ 2 µM 
0.002 ̶ 2 µM 
Trace metals
c
 
nM ̶ µM 
nM ̶ µM 
a
HCO
3
-
/CO
3
2-
depending on the water pH (environmental pH range: 6.5-9). 
b
H
2
PO
4
-
/HPO
4
2-
depending on the water pH. 
c
Mainly As, Cu, Zn, Pb, Cd, Mn