Metrohm 746 VA Trace Analyzer User Manual
Page 487
6 Data processing and evaluation
746 VA Trace Analyzer / 747 VA Stand
6-24
6.9.4
Standard addition
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 automati-
cally and is programmed with the following instructions and parameters on the dia-
log page "OP.SEQUENCE" (see section 5.7.3):
(ADD...ADD)n
Loop for standard addition
n
Number of standard additions
ADD...
Constant standard addition
Soln.name
Name of the standard addition solution
V.add
Addition volume
PADD...
Proportional standard addition
Soln.name
Name of the standard addition solution
Prop.subst.
Name of the reference substance for
proportional standard addition
Prop.coeff.
Proportionality coefficient
V.add = EV:
The remaining parameters needed for the standard addition are entered on the
dialog page "SUBSTANCES/Calibration" (see section 5.6.3). The most important of
these are:
Technique
Selection of the calibration technique
std.add
Standard addition
Curve type
Curve type for calculation of the standard addition
linear
Straight line of type
y = a + bx
nonlin
Curve of type
y = a + bx + cx
4
Soln.name
Name of the standard addition solution (must be identical
to the name specified in the ADD instruction)
Mass conc.
Mass concentration of the standard addition solution
In the standard addition, the following procedure is used to calculate the sought
mass concentration
ρ
eff,s
eff,s
of the sample (see also example in section 4.2):
1
Measurement of the sample solution
The sample solution with the unknown mass concentration
ρ
eff,s
eff,s
of the sam-
ple is measured one or more times. This gives:
EV
s
Evaluation quantity for sample
EV
s
.mean
Mean value of the evaluation quantity for sample
Std.dev.
Standard deviation of the individual value
EV
s
2
Measurement of the spiked sample solutions
The sample solution is spiked one or more times with a standard solution of
known mass concentration
ρ
std
std
. Each of these spiked solutions is measured
one or more times. This gives:
EV
n
Evaluation quantity for n
th
spiked sample
EV
n
.mean
Mean value of the evaluation quantities for
n
th
spiked sample
Std.dev.
Standard deviation of the n
th
individual value
EV
n