Chlorine analysis with the Cl module 5100
multi EA 5100
48
8
Chlorine analysis with the Cl module 5100
8.1
Function and design
8.1.1
Function and measuring principle
Expansion of the basic module with the detection module allows determination of the
chlorine content in solid, liquid, paste-like, viscous and gaseous samples. When doing
so, the device will determine the bromine and iodine content as proportions of the total
chlorine of the sample as well. Fluorine is not detected.
Organic halogen compounds can be determined as TX, AOX and EOX sum parameters
with the analysis system. Inorganic halogen compounds are only determined if they can
be digested via the combustion furnace. Halogen hydracids or pure halogens cannot be
analyzed.
Organic halogen compounds are incinerated into hydrogen halogen, carbon dioxide and
water in the basic module.
The measuring gas flow is routed to the detection module via a transfer line and dried
there. The hydrogen halogens (HCl, HBr, Hl) are determined there via microcoulometric
titration. Hydrogen flouride (HF) is not determined.
In the first step, hydrogen chloride HCl* dissolves in the electrolyte, and dissociates to
hydrogen and chloride ions (H+, Cl-) In the measuring cell, the chloride ions react with
silver ions created via electrolysis to form silver chloride (AgCl). To achieve the most
complete reaction to AgCl, titration is carried out in a strong acetic acid electrolyte. The
solubility product of AgCl is reduced in the acetic acid electrolyte.
R-X + O
2
→ HX + CO
2
+ H
2
O
HX* → H
+
+ X
-
Ag → Ag
+
+ e
-
Ag
+
+ X
-
→ AgX
R: Hydrocarbon residue, X: Cl, Br, I, * HBr und HI are determined as proportions of AgBr
and AgI.
The end point of the titration is displayed potentiometrically. In accordance with Fara-
day's law, the amount of chloride ions can be calculated from the amount of charge ex-
pended to create the silver ions.
8.1.2
Design
The detection module consists of the following main components:
¡
Wide-range coulometer for amperometry and potentiometry
¡
Stirrer/cooling block for the measuring cell (with automatic cell detection)
¡
Measuring cells with electrodes
¡
Sulfuric acid container with safety attachment and gas inlet
¡
Connections, interfaces
¡
Electrode containers
