48 February / March 2019
Figure 5. Benzothiophenes presented by ion chromatograms at m/z 184, 198, 212, 226 and 240 respectively in the range time of 18-45 min.
3.6. Linear Alkylbenzens (LABs)
A very important group of pollutants found in the sediment river samples are Linear Alkylbenzenes (LABs). This group of compounds was the subject of investigation in many early papers [7,16,17]. They can be seen by extracting the ion chromatogram at m/z 91 on fraction a. This class of compounds originates from the biodegradation of alkyl sulfonic surfactants which are present in numerous detergents. They comprise isomers of LABs with a number of carbons from 10 to 13 (Figure 6). The investigation of linear alkyl benzenes is performed in order to study the impact of sewage water on aquatic sediments.
3.7. Trialkylamines and 2M-Ketones
Trialkylamines (TAMs) are cationic surfactants that originate from detergents. Methyl- ketones are photo-oxidation products of TAMs produced in sedimental conditions.
The detection of these families of compounds is very important in studying the impact of sewage water on the sediment organic matter composition [18,19].
Based on chromatogram at m/z 58, two families of organic compounds can consecutively be detected: methyl- ketones and trialkylamines, as can be seen in the Figure 7, using fraction c. The general structure of TAMs used as cationic
surfactants is (CH3 N-Cn )2 H2n+1 (n=12, 14,
16, 18). The ion to m/z 58 originating from methyl-ketones is produced by a rearrangement process, leading to the structure CH3
-(CO+.H)=CH2
. The ion at m/z
58 is also produced from trialkylamines by a fission reaction involving C-C bond along of the amine chain (beta-position) lading to structure (CH3
)2N+ =CH2 4. Conclusions
In the sediment samples collected from the Somes river, several important groups of molecular markers were identified. These detected groups of markers and their main characteristic are shown in Table 1. The main advantage of the GC-MS method
.
Figure 6. GC/MS Chromatogram of m/z 91 for a sediment rivers sample for visualisation of Lineal Alkyl Benzenes (LABs). The alkyl n range 10-13.
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