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3 Maintenance
3.3 Interfering ions
Measuring ion
Interferences
Ag
+
Hg
BF
-
c(NO
4
c(CH
Br
-
Hg
c(OH
c(S
c(S
Ca
2+
c(Na
c(Cu
2+
Cd
Ag
Fe
of the measuring ion.
Cl
-
Hg
c(OH
c(S
c(S
-
CN
S
c(Cl
2+
Cu
Ag
Cl
concentration of the measuring ion.
F
-
c(OH
I
-
Hg
c(Cl
c(S
+
K
c(Na
c(Cs
Na
+
glass
pH > (pNa+4); c(Li
c(Ag
Na
+
polymer
SCN
c(K
NO
-
c(Br
3
c(CH
40
•
The electrode may be too old (ionophore leached out). Use new
electrode tip or new electrode.
The following table shows the concentrations of interfering ions in mol/L
which produce an error of app. 10 %.
2+
must be absent. Proteins should also be absent.
) < 5 ⋅ 10
-
-3
; c(SO
3
-
COO
) < 0.2; Precipitate halides with silver sulphate.
3
2+
must be absent.
-
) < 3 ⋅ 10
4
⋅ c(Br
-
⋅ c(Br
2-
) < 10
-6
-
); c(CN
2-
) < 20 ⋅ c(Br
-
O
)
2
3
+
) < 0.26; c(Pb
2+
) < 5.3 ⋅ 10
) < 6.7 ⋅ 10
2+
-5
; c(Mg
+
2+
2+
, Hg
and Cu
must be absent.
3+
and Pb
2+
interfere if their concentration is higher than the concentration
2+
must be absent.
) < 80 ⋅ c(Cl
-
-
); c(Br
2-
) < 10
-6
⋅ c(Cl
-
); c(CN
⋅ c(Cl
O
2-
) < 10
-2
-
)
2
3
2-
+
and Ag
complexing substances have to be absent.
⋅ c(CN
-
) < 10
6
-
); c(Br
+
2+
2-
, Hg
and S
must be absent.
-
, Br
-
, I
-
, Fe
3+
, and Cd
-
) < 10
-1
⋅ c(F
-
)
2+
must be absent.
-
6
⋅ c(I
-
) < 10
); c(Br
⋅ c(I
O
2-
) < 10
5
-
)
2
3
+
) < 5 ⋅ 10
-1
; c(TRIS
) < 1 ⋅ 10
+
-4
; c(H
+
) < 5 ⋅ 10
+
+
) < 3 ⋅ 10
-7
-
and organic lipophile ions (e. g. acetate) should be absent.
+
+
) < 0.15; c(Li
) < 1; c(Ca
-
) < 7 ⋅ 10
-4
; c(NO
2
COO
-
) < 0.1
3
) < 5 ⋅ 10
2-
) < 0.2; c(ClO
-
4
4
-
) < 4 ⋅ 10
2
⋅ c(Br
); c(Cl
) < 8 ⋅ 10
⋅ c(Br
-
-5
-
); c(NH
-6
; c(Fe
2+
) < 6.7 ⋅ 10
) < 8.3 ⋅ 10
2+
-3
) < 3 ⋅ 10
⋅ c(Cl
-
-3
-
); c(I
-
) < 2 ⋅ 10
-7
⋅ c(Cl
-
); c(NH
) < 5 ⋅ 10
⋅ c(CN
-
3
-
); c(I
2+
interfere if their concentration is higher than the
-
) < 5 ⋅ 10
3
⋅ c(I
-
2-
); c(S
+
+
) < 0.1; c(Li
) < 1; c(NH
) < 1 ⋅ 10
-2
-2
; c(K
+
) < 0.1; c(Rb
2+
) < 1; c(Mg
-
) < 7 ⋅ 10
-4
; c(SO
2-
) < 1; c(Cl
4
-7
; c(F
-
) < 0.6;
-
-
) < 2 ⋅ 10
-4
⋅ c(Br
); c(I
) < 2 ⋅ c(Br
-
);
3
-5
; c(Zn
2+
) < 2.6 ⋅ 10
) < 5 ⋅ 10
⋅ c(Cl
-
-7
-
);
) < 0.1 ⋅ c(Cl
-
);
3
⋅ c(CN
-
) < 10
-1
-
)
-6
⋅ c(I
-
-
) < 0.4 ⋅ c(I
) < 10
); c(CN
+
) < 3.3 ⋅ 10
-3
4
+
) < 3; c(NH
+
4
2+
+
) < 1; c(NH
) < 1; c(H
4
-
) < 2.5 ⋅ 10
-2
Ion-selective electrodes, Manual
-
);
-6
;
-
);
;
) < 3;
+
) < 1
; c(F
-
) < 1;
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