Xylem photoLab 6600 UV-VIS - Manual (Page 61)

photoLab
®
6600 UV-VIS Operation
61 ba75848e01 08/2009
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 in this case. 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
formula
(determination of
coefficients)
Linear
function 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 determined reagent blank value and the slope (m) of
the calibration function (Y axis = absorbance, X axis =
concentration). Proceed as described below.
Explanation of the coefficients of the formula:
z a0 = - E0*a1
[E0 = reagent blank value
(absorbance at concentration 0)]
z a1 = 1/m
Reverse value of the slope of the calibration
function
(often referred to as "Factor")
m = slope of the calibration function
z a2, a3, a4, a5 = further coefficients
(when entering 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.