500 D 01/2012
36a
5.11 Procedures for photometric analyses with NANOCOLOR
®
tests when
samples are colored or turbid
These procedures can only be used in connection with the corresponding original
instructions in this
NANOCOLOR
®
manual.
The photometric analysis of water samples with own color or turbidity always
requires determination of a correction value. Colors and turbidities cause increased
light absorption (increased extinction), thus leading to wrong results. Determination
of correction values requires individual procedures for every test.
For example, it is not possible simply to measure the color of the sample without
reagents and then substract this value from the test result. In many cases, the re-
agents alter the color or turbidity of the sample. All changes of the sample during
analysis, such as dilution, addition of chemicals which alter pH or redox state have
to be taken into account. Only the main reagent, which forms the measured color
complex, is not added.
With the
NANOCOLOR
®
photometer, the measurement programme for the correc-
tion value is started after the measurement of the (turbid or colored) sample (value
A) by pressing key
OK
. The instrument asks for the cuvette with the correction value
(value B) and measures the correction. The corrected measurement result is dis
-
played and stored.
Basic procedure:
Determine measuring result as per original instruction = A
Determine correction value as per special instruction = B
Analytical result
= A – B
Exceptions:
Methods, where decreasing extinctions are measured against a
reagent blank value.
In these cases, analytical result = A + B
The corresponding analytical instructions point out this fact.
It is very important to substract only values with equal dimensions (e.g. mg/L N;
mg/L NH
4
; mmol/m
3
; E).
If, in the same matrix, the correction factor for several samples is so low that it can
be neglected, it may be possible to work without correction. However, this conclu-
sion can only be drawn from practical experience and cannot be predicted!
