Extractable organically bound halogens
Extractable organically bound halogens (abbreviated EOX with X for chlorine , bromine and - with restrictions - iodine ) is a chemical-analytically determined sum parameter. Similar to the determination of the AOX parameter (adsorbable organically bound halogens), it is a method for determining all of the organohalogen compounds. The compounds detectable in this way are measured by extraction with a non-water-soluble solvent, for example a hydrocarbon such as isohexane . All compounds that dissolve easily enough in the solvent are recorded.
A distinction must be made between EOX and water samples according to DEV H 8 and EOX of solids and sludge according to DEV S 17.
The methods differ in the separation step and the substances that are recorded. As a result of the separation, an extract is obtained in both cases. This is burned and the resulting hydrogen halides are determined.
EOX in water samples
EOX in water samples is determined according to the German standard method (DEV) H8. The procedure was temporarily included in DIN 38409, but was withdrawn there in 2007. For the determination, a 1 liter water sample is mixed with sodium sulfate to salt out non-polar components and then extracted twice with 25 ml each of pentane , hexane or heptane .
A one-liter volumetric flask serves as the extraction vessel. Since the solvent is lighter than water, it collects in the neck of the flask and is pipetted off from there. The collected extract, in which the extractable constituents are enriched, of twice 25 ml is made up to 50 ml and dried with sodium sulfate.
EOX in solids and sludges
EOX in solids and sludges is carried out according to the method according to DIN 38414-17 (DEV S 17). The sludge or sediment sample is first dried at 105 ° C. Volatile halogen compounds such as organochlorine solvents such as chloroform are lost. Such components must therefore be blown out beforehand and determined as POX.
The dried material is extracted with hexane in a Soxhlet extractor , in a proportion of 20 g of substance with 75 ml of extractant. The extract is evaporated to below 50 ml and made up to exactly 50 ml.
Incineration of the extract and determination
The result of the extraction is an extract, a solution of the sought-after components in a hydrocarbon. A sample of this extract is incinerated, with the halogenated organic compounds being liberated from hydrogen halides such as hydrogen chloride or hydrogen bromide . These hydrogen halides are then determined argentometrically by coulometry , the halide ions forming sparingly soluble precipitates with silver ions.
Process H8 involves burning the extract in an oxyhydrogen flame in a Wickbold apparatus. The method S17 does not specify the method. In practice, devices are used in which, as with the AOX, the sample is burned in oxygen. The combustion apparatus can be an additional part to the existing AOX apparatus or a separate device. The coulometric determination is carried out as with the AOX.
See also
- AOX - Adsorbable Organically Bound Halogens
- DEV - German standard procedure for water, waste water and sludge testing
Individual evidence
- ↑ Organically bound halogens , nei sewa.de
literature
- Hans-Jürgen Voigt: Manual for the investigation of the subsurface of landfills and contaminated sites: Volume 6: Geochemistry , 491 pages, Verlag Springer Berlin Heidelberg, 1998, ISBN 3540594647