Chemical Methods Notes; Chlorine, Chlorine Dioxide, Chlorite - ProMinent DULCOTEST DT4 Instrucciones De Servicio

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Chemical methods notes

Chlorine, chlorine dioxide, chlorite

1. Reagents
In principle, it is also possible to use reagent tablets (e.g. DPD 1, 3 or 4) for analysis
in these cases if such tablets are available and treated accordingly. Undissolved
tablet residues or turbidity in the beam passage of the photometer lead to measuring
errors and should therefore be avoided.
The specified tolerances only apply if LOVIBOND
used.
2. Selectivity
The DPD method used responds to a wide range of oxidation agents, and you
should therefore ensure that only the selected oxidation agent is present. Mixtures,
such as a combination of chlorine and chlorine dioxide, merely supply cumulative
values and therefore need to be broken down using additional steps. In this case
(chlorine + chlorine dioxide), for example, you should select the procedure "free
chlorine" and conduct two measurements:
a) Standard procedure in line with the description "free chlorine"
b) Dissolve one glycine tablet in a 10 ml sample and add this
to the vial already containing the two reagents
Calculation: Chlorine
Chlorine dioxide = b x 1.9 in mg/l ClO
Alternatively, the chlorine dioxide can be selectively driven out of the sample using
the battery-operated beater.
In the same way the result of a DPD measurement of a mixture of chlorine dioxide
and chlorite (by DPD Chlorine dioxide tablets Nr. 1+2) is a sum value. In this case
the tendency of chlorine dioxide to degase easily leads to erroneous measurements.
So it is recommended to degase the chlorine dioxide totally before measuring
chlorite as it is decribed in the standard procedure "chlorite".
In water containing bromide and iodide, the free - and possibly combined - halogens
formed by the chlorination process are listed as chlorine.
A steady increase in the measuring result for a sample indicates that a further
oxidation agent is present in addition to the selected one, and that this agent is
affecting the measurement process for some reason (far higher concentration,
equilibria, high temperature). These interferences are known in the systems
[combined chlorine ⇒ free chlorine} and {chlorite ⇒ chlorine dioxide]. The resulting
errors can be minimised by fast working and immediate read-off.
3. Vial cleaning
As many household cleaners (e.g. dishwasher detergent) contain reducing
substances, the subsequent determination of oxidation agents (e.g. chlorine) may
show lower results.
®
= (a-b) in mg/l Cl
2
25
/ DULCOTEST reagents are
⇒ result a
⇒ result b
2