V. Zelano . M. Gulmini
The validity of these models and of their related constants is supported by the good
level of agreement between experimental and calculated potentiometric data. As an
example, Table 20.2 reports the differences between calculated (Beale) and experimental
(Bexp) EMF values for some titrations of proton/sediment systems previously considered.
For proton/copper(II)/sediment systems, by using the concentration ofligand sites,
the protonation and the complexation constants that were calculated by refining pHmetric data, it is possible to calculate the concentration of the copper(II) in solution
for each pH value. These calculated values can be compared with those experimentally determined by FAIAAS for each titration point and the comparison may be considered a general validation for the potentiometric method used.
Should the concentration value determined by AAS of copper(II) in solution be
inferior to that calculated from the potentiometric models, this would be an indication of the presence of non-protogenic sites which interact with the copper(II) ions.
On the other hand, significant discrepancies in the opposite sense would indicate that
the models deduced by the potentiometric method do not describe with reasonable
accuracy the real interaction between the sediment and the investigated ions.
Table 20.2. Differences between calculated and experimental EMF values for some titrations taken as
an example from those of MA and VG sediments
%w/v
pHmes
Ecole -Eexp (mV)
%w/v
pH mes
Ecole -Eexp (mV)
(Sediment)
(Sediment)
0.25
2.33
-1.22
1.5
2.36
1.76
(MAl
2.55
-0.56
(MAl
2.64
0.54
2.79
-0.08
2.95
0.20
3.02
0.24
3.29
-0.32
3.31
0.24
3.70
-0.56
3.89
0.05
5.51
0.44
7.97
0.00
6.94
1.63
9.45
1.01
8.52
-1.76
10.06
0.42
9.70
0.07
10.46
0.39
10.32
-0.38
1
2.82
-0.05
1.25
2.83
0.21
(VGl
2.91
0.02
(VGl
2.93
0.29
3.03
0.18
3.04
0.23
3.12
0.16
3.14
0.26
3.25
0.19
3.27
0.18
3.41
0.07
3.43
0.05
3.63
-0.04
3.66
-0.03
3.98
-0.07
3.98
-0.10
4.59
-0.29
4.48
-0.82
7.09
0.31
7.50
-0.41
8.02
-0.44
8.13
-1.79
8.87
-0.17
8.83
-1.26
9.52
0.86
9.42
0.22
9.89
0.37
9.78
0.2
10.15
0.15
10.04
-0.26
10.49
-0.39
10.41
-0.02
10.61
-0.29
10.54
0.10
10.70
-0.08
10.64
0.49
10.82
-0.Q1
10.73
0.93
The validity of these models and of their related constants is supported by the good
level of agreement between experimental and calculated potentiometric data. As an
example, Table 20.2 reports the differences between calculated (Beale) and experimental
(Bexp) EMF values for some titrations of proton/sediment systems previously considered.
For proton/copper(II)/sediment systems, by using the concentration ofligand sites,
the protonation and the complexation constants that were calculated by refining pHmetric data, it is possible to calculate the concentration of the copper(II) in solution
for each pH value. These calculated values can be compared with those experimentally determined by FAIAAS for each titration point and the comparison may be considered a general validation for the potentiometric method used.
Should the concentration value determined by AAS of copper(II) in solution be
inferior to that calculated from the potentiometric models, this would be an indication of the presence of non-protogenic sites which interact with the copper(II) ions.
On the other hand, significant discrepancies in the opposite sense would indicate that
the models deduced by the potentiometric method do not describe with reasonable
accuracy the real interaction between the sediment and the investigated ions.
Table 20.2. Differences between calculated and experimental EMF values for some titrations taken as
an example from those of MA and VG sediments
%w/v
pHmes
Ecole -Eexp (mV)
%w/v
pH mes
Ecole -Eexp (mV)
(Sediment)
(Sediment)
0.25
2.33
-1.22
1.5
2.36
1.76
(MAl
2.55
-0.56
(MAl
2.64
0.54
2.79
-0.08
2.95
0.20
3.02
0.24
3.29
-0.32
3.31
0.24
3.70
-0.56
3.89
0.05
5.51
0.44
7.97
0.00
6.94
1.63
9.45
1.01
8.52
-1.76
10.06
0.42
9.70
0.07
10.46
0.39
10.32
-0.38
1
2.82
-0.05
1.25
2.83
0.21
(VGl
2.91
0.02
(VGl
2.93
0.29
3.03
0.18
3.04
0.23
3.12
0.16
3.14
0.26
3.25
0.19
3.27
0.18
3.41
0.07
3.43
0.05
3.63
-0.04
3.66
-0.03
3.98
-0.07
3.98
-0.10
4.59
-0.29
4.48
-0.82
7.09
0.31
7.50
-0.41
8.02
-0.44
8.13
-1.79
8.87
-0.17
8.83
-1.26
9.52
0.86
9.42
0.22
9.89
0.37
9.78
0.2
10.15
0.15
10.04
-0.26
10.49
-0.39
10.41
-0.02
10.61
-0.29
10.54
0.10
10.70
-0.08
10.64
0.49
10.82
-0.Q1
10.73
0.93