XD 7500
Operation
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04/2018
Determining the cal-
ibration function
You have the following options to create a method:
Measure and store:
Carry out a series of measurements with the following sample solutions
while at the same the photometer takes over the values:
– Blank sample for determination of the reagent blank value
(with deionized water instead of sample, see Section 4.5.9)
– at least one, up to ten standard solutions in different concentrations.
The photometer stores nominal value/absorbance value pairs of the indi-
vidual measurements and determines the resultant characteristics of the
calibration. When doing so, you can select the following line types:
Poly-
gon line
,
Straight line
or
Parabola
.
Enter as value pairs:
Entry of the value pairs, Nominal value (concentration) / Measured absor-
bance of an already available test series with the following sample solu-
tions:
– Blank sample for determination of the reagent blank value
(with deionized water instead of sample, see Section 4.5.9)
– at least one, up to ten standard solutions in different concentrations.
Based on the entered value pairs, the photometer determined the charac-
teristics for the calibration. When doing so, you can select the following
line types:
Polygon line
,
Straight line
or
Parabola
.
Enter a function:
Entry of a function to calculate the concentration from the absorbance
(reverse calibration function). On the photometer, you can enter the coef-
ficients of a polynomial equation of the following type:
c = a0 + a1·A + a2·A
2
+ a3·A
3
+ a4·A
4
+ a5·A
5
If a linear function (straight line) should be entered, it is necessary to enter
the coefficients a0 and a1 to receive correct measured values.
with:
c
Measurement result, e.g. concentration
a0 to a5
Coefficients (input range 0.000 to 1000.000)
A
Absorbance
Entering the formula is especially simple if you measure with a
commercial test set for which the manufacturer has given the
value for the coefficients a1. It is often called the "Factor" and
corresponds to the reciprocal value of the slope of the straight
line of the calibration function.
