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