Operation
XD 7500
64
ba77191e01 - 71310060
04/2018
If the exact value for a0 is not known at the time the formula is entered, it is
sufficient to enter the coefficient a1. In this case, the
User-defined blank value
function (in the
Concentration
/
Setup
menu) has to be activated to measure
with this method.
Prior to measuring with this method, a blank value measurement has to be
carried out. This procedure determines the value for a0, which then replaces
the value from the programming of the method.
If the
User-defined blank value
function is not activated, the photometer uses
the value zero for the coefficient a0.
More information on
the entry of the for-
mula (determina-
tion of coefficients)
Linear func-
tion
If the value for a1 (slope of the reverse calibration function)
is unknown, you can very simply program the method in
the photometer by measuring/storing or entering the value
pairs (see above).
For entry as a formula, you can determine the coefficients
of the reverse calibration function by linear regression.
When doing so, the concentration has to be on the Y axis
and the absorbance on the X axis.
In the case of a linear function, the coefficients of the
reverse calibration function can also be determined from
the reagent blank value determined and the slope (m) of
the calibration function (Y axis = absorbance, X axis = con-
centration). Proceed as described below.
Explanation of the coefficients of the formula:
a0
= - E0*a1
[E0 = reagent blank value
(absorbance with concentration 0)]
a1
= 1/m
Reciprocal of the slope of the calibration function
(frequently called the "factor")
m = slope of the calibration function
a2, a3, a4, a5
= additional coefficients
(for entry of a linear function: zero)
Nonlinear
function
The coefficients of the reverse calibration function are
determined by multiple regression. When doing so, the
concentration has to be on the Y axis and the absorbance
on the X axis.
