Metrohm 797 VA Computrace - Manual (Page 155)

5.8 Data processing and evaluation
797 VA Computrace – Software
143
c(s) = Amount / Sample amount
Note: With the electroplating modes CVS and CPVS different Cali-
bration techniques are used.
Dilution calculation
In all cases in which the sample volume is diluted in the measuring
vessel (e.g. by addition of buffer) before the start of the first sweep,
this must be taken into consideration by entering the two parame-
ters
Sample amount and Cell volume on the Determination tab of
the EDIT WORKING METHOD PARAMETERS window (see
Determination, section 5.2).
If the sample is additionally diluted after the start of the first sweep
(e.g. by standard addition solutions), the dilution is recalculated
continuously for every dilution step so that the effective mass con-
centration of the analyte in the measuring vessel is shown in the
calibration curve for each measurement solution.
If an auxiliary solution is added by a
Dosing Device using the Use
for predose or Use after sample transfer function, this volume must
be taken into consideration by modifying the Cell volume manually.
Standard addition calculation
In the standard addition method, a known amount of the analyte is
added once or several times to the sample. The addition may be
performed manually or automatically using a
Dosing Device . The
following procedure is used to calculate the sought mass con-
centration of the sample:
1. Measurement of sample solution
The sample solution with the unknown mass concentration c(s)
of the sample is measured one or more times (defined by
No. of
replications ). This gives:
EV(s)
Evaluation quantity of a single measure-
ment for the sample
mean(s)
Mean value of all evaluation quantities for
the sample
Std.dev.(s)
Standard deviation of the individual value
EV(s)
= s(s)
2. Measurement of spiked sample solutions
The sample solution is spiked n times (defined by No. of addi-
tions ) with a standard solution of known mass concentration
c(st). Each of these spiked solutions is measured one or more
times (defined by
No. of replications ). This gives:
EV(n)
Evaluation quantity of a single measure-
ment for the spiked sample n