19892 Environ Sci Pollui Res (2015) 22:19887-19895 Ô Springer Time [min] Fig. 3 Time-dependent release of silicone oligomers from silicone strips of different batches using ASE at constant temperature and solvent (100 °C, hexane/acetone (1:1)) typical repeating peaks of silicone oligomers, with the peaks containing the ions m/z 73, 147, 221, 282, 355 and 429, finally leading to silicone coating of GC finer and column. In all different pre-clean-up procedures used, a significant amount of mass (>2 %) was released from the PDMS strips (Table 3). While the swelling of the PDMS strips was highly variable from 42 % (ASE) to 124 % (extraction with hexane/ acetone), release rates were quite uniform, all above 2 %, ranging from 2.2 % (ASE) to 2.5 % (Soxhlet extraction with ethylacetate and extraction with hexane/acetone). Silicone rubber pre-cleaning with ASE takes only 70 min and is thus much faster as other classical pre-cleaning methods like Soxhlet or shaking extraction (36-100 h) (Smedes and Booij 2012; Shahpoury and Elageman 2013). Thus, ASE-based methods enhance the suitability of sili cone rubber samplers for routine applications profoundly as it reduce labour time considerably. In addition, no long term preparation of campaigns is necessary, making this sampler type suitable for deployments on short notice (which is not possible using traditional clean-up methods). Although the silicone sheets have been thoroughly pre cleaned, traces of oligomers are still co-extracted during sam pler extraction after deployment. Quantitative determination of silicones was not carried out by GC or GC-MS because they quickly destroy the GC performance. Instead, we found that TXRF proved to be a very fast and easy procedure to detect and quantify silicone oligomers. Measurements with TXRF revealed that more than 90 % of extractable silicone oligomers could be removed by the pre-cleaning step with ASE similar to other cleaning procedures. Thus, further cleanup of the sample extract is still mandatory to avoid instrument interferences, such as silicone coating of gas chromatography (GC) liners. Optimization of the organic solvent for ASE extraction Results of the solvent extraction experiments using ASE showed that the analytes were extracted within the first 10 min. The recovery rates of IS (CHC and PAH) increased with decreasing polarity of the solvent (Fig. 4). Within the more polar solvents (acetonitrile and acetonitrile/methanol) recovery rates were better for aromatic compounds with 4- or more rings like fluoranthene, benz[e]pyrene and benz[ghi]perylene (56-108 %) than for the more volatile 2- and 3-ring aromatic compounds naphthalene, acenapthene and anthracene (4-32 %). Polar solvents need to be transferred to non-polar solvents as recommended by Smedes and Booij (2012), and this addi tional step may be responsible for lower recovery yields of lower boiling point analytes (2- and 3-ring PAH, e-HCH and TCN). Thus, in terms of better extract efficiencies and higher recoveries of non-polar contaminants, non-polar extraction solvents such as hexane or dichloromethane should be used. However, non-polar extraction solvents co-extract more sili cone oligomers, simultaneously. Therefore, an additional cleanup step is necessary, which was performed by HPLC- SEC as described in “Removing silicone oligomers from sam ple extracts by HPLC-SEC”. Fig. 4 Recovery rate of internal CHC and PAH standards using different solvents (dichloromethane, acetonitrile) and solvent mixtures (n-hexane/ acetone (1:1 v/v); acetonitrile/ methanol (2:1 v/v)) by ASE extraction (n=2 for each solvent (-mixture)) Solvent NAPH-D8 ACE-D10 ANT-D10 FLU-D10 1 BEP-D12 BGHIP-D12 e-HCH TCN CB185