Metrohm 797 VA Computrace Manuel d'utilisateur télécharger pdf (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

Nonlinear curve of 4

degree =

Nonlinear Regression

y = b x+ d x

Nonlinear curve of 4

degree through

zero point = Nonlinear Regression

(trough Zero)

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Metrohm 797 VA Computrace Manuel d'utilisateur Page 158

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