multi N/C pharma HT
Function and design
33
3.7
Blank values
3.7.1
Water blank values
Preparation water blank value
Especially for measurements with low TOC concentrations (µg/l range), the TOC content
of the water used to prepare the standard solutions must be taken into account. The
concentration of the standard solution and the TOC blank value of the preparation water
are often within the same range. This blank value can be taken into account during cali-
bration.
The TOC content of the preparation water is measured separately before the calibration.
The software then subtracts the average integral determined for the preparation water
for each measuring point of the calibration from the determined gross integral.
I
Net
= I
Gross
– I
Preparation water
The software determines the calibration function from the net integrals. Mathemati-
cally, this corresponds to a parallel movement of the calibration line.
The software also takes the preparation water blank value into account when determin-
ing the daily factor.
Diluent blank value
If the sample is diluted, the blank value for the diluent is of interest. This value can be
determined separately or entered manually in the software. The software takes the dilu-
ent blank value into account when calculating the concentration of diluted samples.
The diluent blank value can change over time and must therefore be determined again
before beginning a measurement series. Otherwise, the software will use the last value.
The diluent blank value is always indicated in the software normalized to a volume of
1 ml.
Diluent blank value use
The software calculates the actual diluent integral (I
DiBV
) for each measurement based on
the diluent blank value, the sample volume used and the dilution ratio. The software
then subtracts the diluent integral (I
DiBV
) from the experimentally determined raw inte-
gral (I
Raw
).
I
DiBV
= V
DiBV
x (V
Sample
– N
P
/N
D
x V
Sample
)
I
eff
= I
Raw
– I
DiBV
V
DiBV
: Diluent blank value
V
Sample
Sample volume
I
eff
: Effective integral
N
P
: Number of units of the primary sample
N
D
: Number of units of the diluent
I
Raw
: Raw integral
I
DiBV
: Diluent integral
Diluent indication
Proportions of the primary probe: in total proportions (e.g., 10 parts in 100 parts)
This means that 10 ml of the primary sample is filled to a total volume of 100 ml with
dilution water.
A 1:1 dilution ratio equals I
DiBV
= 0.
Calculation of the sample con-
centration
To calculate the sample concentration c, the sample volume and the dilution ratio are
used:
c = m/V
Sample
x N
D
/N
P
