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Deliverables
A method was developed subjecting the asphalt sample to a soxhlet extraction with CH2Cl2 (2mL solvent per g asphalt) during 4 hours. For purification of this extract, a liquid-liquid extraction method was developed transferring the phenols from the CH2Cl2 phase into an alkaline aqueous solution at pH 14. The recovery of this step in the presence of matrix was determined (100% for phenol, but only 34% for 1,3,5 trimethylphenol. The alkaline solution is neutralized, filtered and directly injected into HPLC. An isocratic reversed phase HPLC method using a special C18 column with polar modification was developed for an appropriate separation of the 10 selected phenols. Quantification of the phenols is carried out using individual external calibration. The use of a UV photodiode array detector enables peak identification. For the application to the asphalt samples, trace determination capability was required, since several phenols are present below 1ppm.
A 3 step batch extraction under sonication was developed to extract contaminants from asphalt. 5mL CH2Cl2 are applied per g asphalt, sonication is applied for 15 minutes and the solid residue and supernatant are separated by centrifugation. To the combined extracts a defined amount of C23 is added as internal standard. Then 100µL of the organic extracts in CH2Cl2 obtained as described above are deposited on a small, dry, silica gel column (55mm x 5mm) for purification. A Pasteur pipette can be used for that purpose.
The first fraction (1000µL) eluted with CH2Cl2 contains the PAH. This fraction can be directly injected into the GC applying a standard method for separation of the 16 EPA PAHs. Quantification of PAHs using a flame ionisation detector is carried out relative to C23 considering the individual ratio of C-atoms.
Applying alternatively the highly selective mass spectrometric detection, individual calibration curves (relative to C23) were recorded and considered for quantification. The methods were validated for application with the original course asphalt sample and with a fine homogeneous powder obtained by milling. It turned out that only the milling of the asphalt prior to subdividing and extraction enables separation of representative aliquots and reliable analysis.
Following the protocol for a HPLC method described under result 5, the quantitative determination of the original PAH content in the selected asphalt sample 2702/4 (Einstreudecke grob / Juchem) was carried out. The global PAH content determined with this method was 4794mg/kg and thus by 50% higher than the value determined with GC-MS. The pattern of distribution of the 16 PAHs, however, was similar. The significantly higher amount must be attributed to the poorer chromatographic resolution and the less selective detection. Since the matrix of asphalt is very complex the bias of quantification is very high with HPLC-UV. From this result the conclusion was drawn to carry out PAH analysis in the project only by GC and GC-MS.
Applying the HPLC method described under result 6, the determination of the original concentration of phenols was determined in the same sample. The results in mg/kg were phenol (3.8), 3-,4-methyl phenol (3.2), 2-methyl phenol (1.0), 2,6-dimethyl phenol (5.2), 4- ethyl phenol (1.0), 2,4-dimethyl phenol (1.0), 2-naphthol (0.2), 2,4,6-Trimethyl phenol (1.0), 1-Naphthol (not found). The total amount of small phenols in sample 2702/4 is thus 16.2mg/kg.
A method was developed subjecting the asphalt sample to a soxhlet extraction with CH2Cl2 (2mL solvent per g asphalt) during 4 hours. The extract was purified on a silica column following the protocol described under result 4. From the eluted solution the CH2Cl2 was evaporated under rotation at 100 mbar and the residue was filled up to a defined volume with methanol.
The methanolic solution could be directly injected into HPLC. An elution gradient reversed phase HPLC method using a standard C18 column was developed for an appropriate separation of the 16 EPA PAHs, since no specialized PAH column was available.
The recovery for the complete sample preparation procedure was determined for each individual PAH (between 81% for naphthalene and 99% for phenanthrene). Quantification was carried out using individual external calibration. The use of a UV photodiode array detector enabled peak identification and individual optimisation of selective detection wavelength.
Following the GC- and GC-MS methods, the quantitative determination of the original PAH content in the selected asphalt sample 2702/4 (Einstreudecke grob / Juchem) was carried out.
The most reliable results were obtained, when the method was applied to the finely milled sample and quantification was carried out by GC-MS. The determined PAH contents in mg/kg were naphthalene (9), acenaphthylene (<0.1), acenaphtene (97), fluorine (133), phenanthrene (955), anthracene (261), fluoranthene (550), pyrene (407), benzo(a)anthracene (136), chrysene (129), benzo(b)fluoranthene (85), benzo(k)fluoranthene (60), benzo(a)pyrene (126), indeno(1,2,3-cd)pyrene (69), dibenzo(a,h)anthracene (19), benzo(g,h,i)perylene (67). The global concentration of PAHs is thus determined as 3103mg/kg.
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