Metrohm tiamo 2.3 (process analysis) - Manual (Page 948)

5.6 Commands ￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭
932 ￭￭￭￭￭￭￭￭ tiamo 2.3 (for Process Analysis)
the aid of a CALC command according to the following formula ( ρ= den-
sity in g/mL):
Caution
The values for the axis intercept E(0), the slope s and the concentration
c
A
can only be iteratively recalculated out of voltages U
i
measured for
the sample and the spiked solutions and the known concentration of
the standard which requires a lot of effort because it is about an equa-
tion system with 3 unknowns. At least, the concentration c
S
is easily
recalculable with the values for E(0), U
S
and s calculated by tiamo (see
following example).
Example
￭ Parameters
Concentration of the standard addition solution = 1000 ppm
Volume of the standard addition solution V
add
= 10 mL
Sample size V
S
= 10 mL
￭ Measured data
dV
(mL)
U
(mV)
dU
(mV)
Sam-
ple 59.8
Incre-
ment
1 0.310 39.9 -20.0
Incre-
ment
2 0.705 19.9 -20.0
Incre-
ment
3 1.750 -1.1 -21.0
￭ Results
E(0) = 129.7
s = -61.5
c(F
- ) = 27.4 ppm
￭ Recalculation
c
A
= 10 ^((59.8 − 129.7) / -61.5) = 13.696
c(F - ) = (10 + 10) / 10 * 13.696 = 27.39 ppm