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

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 pro posed as a rapid tool for the investigation of different types of sediment contaminations. Such rapid investigations allowed to increase the number an d the frequency of the controls of river sediments, which are generally tim e and money consuming. However, during flash pyrolysis, the molecules gener ated derive from both macromolecules breakdown and thermovaporization of fr ee compounds. Then, a methodology allowing the fractionation of these two t ypes of effluents should be developed. Two river sediments showing differen t contamination degrees have been investigated in order to test the differe nt modes of pyrolysis. The efficiency of thermodesorption-gas chromatograph y-mass spectrometry (TdGC-MS) at low temperature (300 degreesC) for the stu dy of free molecules (PAH, hydrocarbons,...) is compared with the results d erived from traditional analysis (extraction, liquid chromatography and GC- MS). On the other hand, pyrolysis of pre-thermodesorbed sediments is carrie d out in order to analyze the residual organic matter. However, the use of thermodesorption instead of solvent extraction for free organic matter remo val is not always efficient especially for high molecular mass compounds. O n the other hand, although heavy molecular mass compounds are frequently un derestimated. the use of TdGC-MS remains an efficient tool for the rapid sc reening for contaminant investigation. Moreover, low molecular mass organic compounds which are generally lost during traditional pre-treatment (extra ction followed by reconcentration steps) are detected after thermodesorptio n of the raw sediment. (C) 2001 Elsevier Science B.V. All rights reserved.