This analysis is performed using gas chromatography. Organic halogenated compounds in water can almost entirely be traced back anthropogenic emissions. Where they are found in the environment, these compounds serve as indicator substances for industrial pollution. Moreover, they can be produced through application of oxidizing agents during water and wastewater treatment. They are introduced through improper treatment or bad practices. Furthermore, formation through the degradation of higher molecular organohalogen derivatives is possible.
Drinking water intended for use as an ingredient in the production of beer (brewing liquor) or other foods
Due to physico-chemical properties of these substances, a number of effective enrichment processes are available for analysis using gas chromatography and can be summarized as follows:
pentane extraction
adsorption onto solid materials using thermal desorption (purge and trap)
headspace techniques
Pentane extraction
The sample is cooled with ice and extracted using chilled pentane. Subsequently, the pentane phase is separated with a micro separator.
Purge and Trap
The purge gas, as a rule, the carrier gas of the gas chromatograph, passes through the exhaust vessel filled with the water sample. Through stripping, the volatile substances are driven out and then accumulate on the sorbent, e.g., Tenax. After the stripping process is complete, the substances are thermally desorbed by rapidly heating the adsorber column. They are then conveyed to the gas chromatograph through a heated transfer tube.
Headspace techniques
The static headspace method is an ideal technique for the analysis of the volatile substances found in water, due to the simple sample preparation and the substantial sensitivity of the analysis. A further advantage of this procedure is that particulate matter as well as other substances present in the sample with a low volatility and high molecular weight do not interfere with the analysis, since they are not carried by the steam into the headspace and are therefore do not reach the separation system. Moreover, the high degree of automation combined with the aforementioned short time required for sample preparation allows for a rapid, precise and user-friendly analysis for water samples.
Gas chromatography
For the gas chromatographic analysis, an electron capture detector (ECD) is employed due to its high selectivity and high sensitivity. If the ECD is combined with a flame ionization detector (FID), methylene chloride, benzene and its homologues can also be analyzed. With the aid of cryo-focusing, this method can be adapted to detect more volatile substances, such as vinyl chloride or chlorofluorocarbons.