Metrohm tiamo 2.4 Manual - Manual (Page 954)

5.6 Commands
￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭
938 ￭￭￭￭￭￭￭￭
tiamo 2.4
the aid of a CALC command according to the following formula ( ρ = den-
sity in g/mL):
CAUTION
Recalculating the values for the axis intercept E(0), the slope s and the
concentration c
A
iteratively from the voltages U
i
measured for the sam-
ple and the spiked solutions as well the known concentration of the
standard requires much effort, because it is an equation system with
three unknowns. However, the concentration c
S
can at least be easily
recalculated with the values for E(0), U
S
and s calculated by tiamo (see
the following example).
Example
￭ Parameters
Concentration of the standard addition solution = 1,000 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 0.31 39.9 –20.0
Incre-
ment
2 0.705 19.9 –20.0
Incre-
ment
3 1.75 –1.1 –21.0
￭ Result
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