Metrohm viva 1.1 (ProLab) - Manual (Page 1064)

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1052 ￭￭￭￭￭￭￭￭
viva 1.1 (for process analysis)
Effective addition volume
In order to avoid nonlinearities in the calculation of the regression data, a
quantity must be found that exhibits a direct correlation between the
measured quantity and the x axis of the calibration curve. Usually, this
quantity is the concentration. In the calibration method DT (see Glossary,
page 1050), however, the concentration of the sample is what is being
investigated. The problem is that only the addition volume (i.e. the addi-
tion volume of the standard solution during calibration and the addition
volume of the sample during sample determination) is known.
The measured quantity is, however, not dependent on the added volume
but on the concentration of a substance. The quantity VOL/VTOT, which
is proportional to the concentration of the substance in the measuring
cell, is therefore selected on the x axis for generating the calibration curve.
The effective addition volume VEFF(X) = VOL*VTOT(VMS)/
VTOT(X) is introduced in order for a familiar physical quantity to be able
to be displayed on the x axis.
In the case of a very small addition volume as compared to the volume
VTOT(VMS), the effective addition volume approximately corre-
sponds to the addition volume added.
Fill the measuring vessel with the electrolyte
volume VTOT(VMS).
Add the volume VOL of standard solution or
sample solution.
Thoroughly mix the solution in the measuring
vessel.
Remove the volume VOL from the mixed solu-
tion in order to obtain the original total vol-
ume VTOT(VMS) again.
The effective addition volume VEFF now cor-
responds to the volume of the standard solu-
tion or the sample solution that is still in the
measuring cell.