Xylem photoLab 6600 UV-VIS - Manual (Page 54)

Operation photoLab
®
6600 UV-VIS
54 ba75848e01 08/2009
4.5.9 Reagent blank value
The evaluation of the photometric measurement always refers to the
comparison value of a test sample without the substance to be determined
(reagent blank value). Thus the influence of the basic absorbance of the
reagents on photometric measurement is compensated for.
In practice, the reagent blank value is measured with the same amount of
deionized water instead of sample.
Factory and user-
defined reagent
blank values
With photometric concentration determination, the reagent blank value is a
constant. The method data for all measurements with WTW test sets
(Concentration mode) include an exactly determined reagent blank value.
This value is overwritten if you measure the reagent blank value yourself
(setting, User-defined blank value, see section 4.5.6).
Note
You can increase accuracy if you determine the reagent blank value with a
test of a new lot and use the reagent blank value for all further measurements
with this lot. This is especially recommended for measurements in the vicinity
of the lower limit of the measuring range. To be able to attribute the reagent
blank value in the measured value documentation later, you can enter the lot
number of the reagent package (Lot number) during the blank value
determination.
Validity The factory blank values always remain stored in the meter and can be
activated at any time. The reagent blank values you measured yourself also
remain stored in the meter until they are overwritten by a new blank value
measurement.
Single and multiple
determination
The reagent blank value can be determined with single or multiple
determination. With multiple determination, the reagent blank value is
calculated as the median from the individual measured values.