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71
C
SAMP
=
C
STD
· V
STD
· f
·
(V
SAMP
+ V
ISA
)
(V
SAMP
+ V
ISA
)
- (V
SAMP
+ V
STD
+ V
ISA
)·10
∆E
V
SAMP
S
∆E - the difference of potential from the elec-
trode;
S - the electrode slope, determined in a previ-
ous calibration;
f
- the stoichiometric ratio between sample
and standard;
where: C
SAMP
- the sample concentration;
C
STD
- the standard concentration;
V
SAMP
- the sample volume;
V
STD
- the standard volume;
V
ISA
- ISA volume
Example 1
You have sulfide samples and you are adding Ag
+
. The reaction is:
One mole sulfide sample reacts with 2 moles silver standard (f =
1
/
2
).
Example 2
You have sulfide samples and you are adding Pb
2+
. The reaction is:
One mole sulfide sample reacts with 1 mole lead standard (f = 1).
Analyte Addition and Analyte Subtraction
Analyte Addition and Subtraction are variations of the previous two methods.
With Analyte Addition, sample (analyte) is added to an ion standard being measured. The
standard and sample contain the same ion. mV are taken before and after the sample addition.
From the mV the analyte concentration is determined.
With Analyte Subtraction, sample (analyte) is added to an ion standard being measured. The
analyte reacts with the measured ion in a known manner thus removing measured ions from the
solution. From the change in mV the concentration of the analyte is determined.
S
2-
+ 2Ag
+
→ Ag
2
S
S
2-
+ Pb
2+
→ PbS
C
SAMP
=
C
STD
· V
STD
·
(V
STD
+ V
SAMP
+ V
ISA
)·10
∆E
- (V
STD
+ V
ISA
)
(V
STD
+ V
ISA
) V
SAMP
S
With Known subtraction, a known standard is added to an ionic sample being measured. The
standard reacts with the measured ion in the sample in a known manner, thus removing measured
ions from the solution. From the change in mV, the concentration of the sample is determined.
C
SAMP
=
f ·{
(V
STD
+ V
ISA
)
-
[1 +
(V
STD
+ V
ISA
)
]·10
∆E
}·(
C
STD
·V
STD
)
V
SAMP
V
SAMP
V
STD
+ V
ISA
S
ADDITIONAL INFORMATION
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