Rapid contamination screening of river sediments by flash pyrolysis-gas chromatography–mass spectrometry (PyGC–MS) and thermodesorption GC–MS (TdGC–MS)

Abstract

For 20 years, pyrolysis-gas chromatography–mass spectrometry (PyGC–MS) has been currently used in order to improve the knowledge on recent (soils and sediments) and fossil complex organic matter. Actually, PyGC–MS is also proposed as a rapid tool for the investigation of different types of sediment contaminations. Such rapid investigations allowed to increase the number and the frequency of the controls of river sediments, which are generally time and money consuming. However, during flash pyrolysis, the molecules generated derive from both macromolecules breakdown and thermovaporization of free compounds. Then, a methodology allowing the fractionation of these two types of effluents should be developed. Two river sediments showing different contamination degrees have been investigated in order to test the different modes of pyrolysis. The efficiency of thermodesorption-gas chromatography–mass spectrometry (TdGC–MS) at low temperature (300°C) for the study of free molecules (PAH, hydrocarbons, …) is compared with the results derived from traditional analysis (extraction, liquid chromatography and GC–MS). On the other hand, pyrolysis of pre-thermodesorbed sediments is carried out in order to analyze the residual organic matter. However, the use of thermodesorption instead of solvent extraction for free organic matter removal is not always efficient especially for high molecular mass compounds. On the other hand, although heavy molecular mass compounds are frequently underestimated, the use of TdGC–MS remains an efficient tool for the rapid screening for contaminant investigation. Moreover, low molecular mass organic compounds which are generally lost during traditional pre-treatment (extraction followed by reconcentration steps) are detected after thermodesorption of the raw sediment.