Metrohm 746 VA Trace Analyzer - Manual (Page 492)

6.9 Content calculation
746 VA Trace Analyzer / 747 VA Stand
6-29
5 Calculation of the mass concentration ρρ
eff,s eff,s
The sought mass concentration ρ
eff,s eff,s
of the sample is calculated by inserting
EV
s
.mean in the calibration function determined earlier:
c ρ
eff,s eff,s
4 + b ρ
eff,s eff,s
– a = EV
s
.mean
In the graphical representation of the calibration curve,
EV
s
.mean
and the
calculated mass concentration ρ
eff,s eff,s
are marked:
cal.crv.
EV
6 Calculation of the mass concentration ρρ
s s
The found, effective mass concentration ρ
eff,s eff,s
is converted into the sought
mass concentration ρ
ss
by taking the dilution into account (see section 6.9.2):
Mass conc. = ρ
ss
= ρ
eff,s eff,s
/ f
VV
7 Calculation of the total scatter MC.dev
The total scatter σ
xx
is calculated from the two error contributions of the
calibration and the measurement as described in section 6.9.3:
( σ
x x
) 22 = ( σ
x,M x,M
) 22 + ( σ
x,C x,C
) 22
As these scatters refer to the effective mass concentration ρ
eff,s eff,s
, they must
also be converted by taking the dilution into account:
MC.dev. = σ
xx
/ f
VV
Meas.dev. = σ
x,M x,M
/ f
VV
Cal.dev. = σ
x,C x,C
/ f
VV
To be able to calculate Cal.dev. , the following conditions for the number of
measured value pairs n in the calibration must be met:
n ≥ 2 for y = bx
n ≥ 3 for y = a + bx
n ≥ 3 for y = bx + cx 4
n ≥ 4 for y = a + bx + cx 4
If this is not the case, Cal.dev.= 0 is set and the message no cal.devia-
tion put out on the "RESULTS/Evaluations" page.
The calculation of Meas.dev. uses the number of measured value pairs m in
the measurement of the sample solution. The following cases must be
distinguished:
ρρ
eff,s eff,s
ρρ
eff eff
EV
s
.mean