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Detection of molecular markers in aquatic sediments by ion profiles obtained by GC/MS system
by Zaharie Moldovan
National Institute of Research and Development for Isotopic and Molecular Technology, 400293 Cluj-Napoca, Str. Donat 67-103, e-mail:
zaha@itim-cj.ro
An analytical method has been developed that permits the determination of molecular markers in aquatic sediments. The procedure consists of ultrasonic solvent extraction followed by a clean-up operation and then analysis by a GC-MS method. The molecular markers are visualised by selected ion chromatograms. The compounds are identified based on mass spectra obtained by Electron Ionisation (EI) in full scan mode.
Figure 1. GC/MS chromatogram of m/z 85 for a sediment sample collected from river for visualisation of n-alkanes (n range 12-26) 1. Introduction
The sedimentary organic matter results from a complex combination of both natural and anthropogenic sources [1-7]. The activities of present-day civilisation have released into the aquatic environment a wide variety of natural and synthetic compounds not found previously. Many of these compounds when found provide a means of identification of sources of input and pathways of movement of chemicals through the ecosystem.
The concentrations of organic compounds in an environmental sample reflect both the original source of organic matter, as well as the alteration processes, which have occurred in the environment. The anthropogenic and naturally occurring compounds are found mixed together in recent environmental samples and several of these compounds may be used as tracers to study natural processes affecting the fate
and effects of chemical contaminants in aquatic sediments.
The sediments constitute archives of environmental processes. In order to differentiate the various inputs of organic matter, molecular marker approaches have been developed on the potential of molecules to be source specific [2-4,8,9].
The purpose of the present paper is the characterisation of organic molecular markers detected in the river sediment by GC/MS analysis to evaluate the degree of contamination and identify the sediment sources in a surface water catchment in Romania. The GC/MS method has the advantage of generating several parameters from a single analysis. The study presents data for several families of organic compounds used as molecular markers [8- 10] in sediment organic matter investigation: n-Alkanes, Acyclic isoprenoid, Pentacyclic triterpanes (Hopanes), Polyaromatic
Hydrocarbons (PAHs), Benzothiophenes, Linear Alkylbenzens (LABs), Trialkylamines (TAMs) and 2M-Ketones.
2. Experimental section
Sample sites The samples were collected from places along a 60 km section (between Cluj-Napoca and Dej, Romania) of the Somes River catchment and were analysed for a large number of organic compounds commonly used as molecular markers for sediment mater composition
Ultrasonic solvent extraction
An aliquot (2g) of freeze-dried sediment was extracted successively with 10 ml CH2
Cl2 :methanol (2:1) 3 times for 15
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