Procedures For Colored Or Turbid Samples; Determination Of Correction Values For Nanocolor Tube Tests - Macherey-Nagel PF-12 Plus Manual

9. Procedures for colored or turbid samples

These procedures can only be used in connection with the corresponding original instruc-
tions in this NANOCOLOR
The photometric analysis of water samples with inherent color or turbidity always requires
determination of a correction value. Color and turbidity causes increased light absorption
(increased extinction), thus leading to wrong results. Determination of correction values re-
quires 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 reagents alter the col-
or or turbidity of the sample. All changes of the sample during analysis, such as dilution or
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
started after the measurement of the (turbid or colored) sample (value A) by pressing
The instrument asks for the cuvette with the correction value (value B) and measures the
correction. The corrected measurement result is displayed and stored. For some tests it is
neccessary to measure an additional blank value.
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
3
mmol/m ; 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!
9.1 Determination of correction values for NANOCOLOR
For measurement of the correction value use a clean, empty test tube filled with distilled
water as a blank value (exceptions: test 0-59 / 0-64 / 0-65 / 0-66).
Test
0-03, 0-04, 0-05, 0-06,
0-08 Ammonium 3–200
0-07 AOX 3
0-09 Lead 5
0-14 Cadmium 2
0-15 Carbonate
hardness 15
0-17 Chlorine/Ozone 2
0-18 Chlorine dioxide 5
®
manual.
® Plus
PF-12 , the measurement program for the correction value is
Test tube for correction (value B)
Proceed as described in the instructions for test 0-03 / 0-04 / 0-05 / 0-06 / 0-08,
but do not add NANOFIX R2, close, mix.
Almost all colors and turbidities are destroyed under test conditions and do not
interfere. Resistant colors and turbidities cause deviating results which cannot
be circumvented.
The original test contains a correction.
Fill empty test tube with 4.0 mL sample, add 0.2 mL R2, close and mix.
Open carbonate hardness test tube, add 4.0 mL sample solution, close, mix
and adjust to zero (value B). Open test tube, add R2, close and shake well.
Measure after 2 min (analytical result = A – B).
Fill empty test tube with 4.0 mL sample for each test.
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tube tests
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