Metrohm 797 VA Computrace - Manual (Page 158)

5 Determination mode
797 VA Computrace – Software
146
Linear Regression: 2 ≥ 3
Nonlinear Regression: 3 ≥ 5
Linear Regression (through Zero): 1
≥ 2
Nonlinear Regression (through Zero): 2
≥ 4
Linear Interpolation: 2 ≥ 2
Quadratic Interpolation: 3
≥ 5
If less than the "Recommended number" of calibration points
are used for the calculation, the regression curve might does
not fit ideally. Therefore you should always use the "Recom-
mended number" of calibration points.
• Finally, the sample is measured and its mass concentration c(s)
determined using the recorded calibration curve.
In the content determination using a calibration curve, the follow-
ing procedure is used to calculate the sought mass concentration
c(s) of the sample:
1. Measurement of calibration solutions
The calibration solutions with known mass concentration c(n)
are each measured several times (defined by
No. of replica-
tions ). This gives:
EV(n)
Evaluation quantity of a single measure-
ment for calibration solution n
mean(n)
Mean value of all evaluation quantities for
calibration solution n
Std.dev.(n)
Standard deviation of the individual value
EV(n)
= s(n)
c(eff,n) Effective mass concentrations of the cali-
bration solutions (calculated from c(n)
taking the dilution into account)
2. Determination of calibration curve
The calculation curve is calculated according to one of the four
possible model functions selected under
Regression technique
on the Substances tab:
y = a + bx Straight line = Linear Regression / Linear
Interpolation
y = bx Straight line through zero point =
Linear Regression (trough Zero)
y = a + b x+ d x
4
Nonlinear curve of 4 th degree =
Nonlinear Regression
y = b x+ d x
4
Nonlinear curve of 4 th degree through
zero point = Nonlinear Regression
(trough Zero)