Environ Sci Pollui Res (2015) 22:19887-19895 
19891 
4) Springer 
Fig. 1 Scheme of silicone rubber 
sample extraction, clean-up and 
analysis 
Extraction 
•ASE 
(100°C, 10 Min, Hexane/DCM (1:1)) 
A 
i 
Extract purification 
•Si0 2 
Extraction (Hexane/DCM (70:30)) 
j 
i 
Removing 
oligomers 
' 
•HPLC-SEC Fractionation 
(60°C, 1ml/mîn, Hexane/DCM (80:20)) 
4 
\ 
Monitoring extract for 
oligomers 
' 
•TXRF (5|jl on sapphire plate) 
à 
\ 
Quantifying 
^ concentrations ^ 
' 
•GC/MSfor CHC 
•GC/MSfor PAHs 
à 
(0-10 min) contained the non-crosslinked silicone oligomers 
and the second fraction the CHCs and PAHs fraction (10- 
28 min). Column temperature was set to 60 °C to avoid adhe 
sion of silicone in the system. The second fraction was con 
centrated to 0.2 mL with nitrogen and monitored for its olig 
omer load with TXRF before instrumental analysis. For this, 
an aliquot of 5 )iL was slowly dropped onto pre-cleaned sap 
phire disc, allowing the organic solvent time to evaporate. The 
disc was loaded into the TXRF and measured for 1000 s for its 
silicium load, which is the representative element of the sili 
cone oligomer. A rubidium reference standard was used for 
instrument calibration. If the silicium load of the sample was 
in the range of SEC blanks, an analysis of CFfCs (GC-MS/ 
MS) and PAFls (GC-MS) was performed. The complete ex 
traction and analysis process is illustrated in Fig. 1. 
Results and discussion 
Optimization of the silicon rubber pre-cleaning 
Different solvents showed different patterns of swelling and of 
total oligomer release (Fig. 2). No swelling and release of 
oligomers was induced by water, while up to 2.3 % of silicone 
oligomers were released when non-polar solvents were used 
(«-hexane/acetone (1:1 v/v)) (Fig. 2). The release of oligomers 
was exponentially dependent on the swelling of the silicone 
strips (R 2 =0.99) (Fig. 2), from 0 to 60 %. In contrast to a study 
of Shahpoury and Flageman (2013), none of the used solvents 
expanded the silicone rubber as drastically as to block the 
solvent flow. Flowever, the blockage might depend on the 
volume of silicone rubber relative to the volume of the extrac 
tion cell. Rusina et al. (2007) showed that PDMS strips be 
came more breakable after increased swelling. Thus, the 1:1 
combination of hexane/acetone was used as the solvent of 
choice in further pre-cleaning experiments, providing a high 
oligomer release rate with medium swelling (20 %). In all 
experiments, PDMS strips regained their original size and 
strength after the drying process (evaporation of the solvent). 
It was found that the amount of released oligomers from 
silicone rubber strips increased with increasing extraction time 
up to 70 min with no further release with increasing time 
(Fig. 3), indicating the oligomer release from the silicone rub 
ber strips to be fairly exhausted. The final amount released is 
dependent on the batch from which the passive sampler strips 
were prepared. 
The variation of temperature showed no differences in the 
amount of released oligomers and hence was excluded as a 
factor for optimization of oligomer release rates. Thus, the 
ASE default temperature of 100 °C was applied. 
Additionally to the determination of the weight of the PDMS 
strips, corresponding extracts were analysed by GC-MS to 
proof the differences in weight to be a result of oligomer re 
lease. All extracts of silicone rubber pre-cleaning showed the 
a> 
E 
o 
cn 
a> 
tn 
« 
a> 
a> 
a: 
n-Hexane/Acetone T 
_ -(1:1) . n-Hexaighyiacetatf 
, n Acetone n-Hexane/ ■ - 
z,u- Acetone (3:1) 
r ‘ Methanol/n-Pentane Acetone (1:1) 
(1:1) 
1,5- 
1,0- 
0,5 - " Methanol/Acetonitrile (1:2) y = yO + A*exp(R0*x) 
R 2 = 0.99 
■ Oligomer release 
0,0 - u water Exponential fit 
I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 
0 5 10 15 20 25 30 35 40 45 50 55 60 
n-Hexane/Acetone 7. 
_ -(1:1) . n-Hexaighyiacetatt 
Acetone n-Hexane/ ■ i 
Acetone (3:1) 
ri Methanol/n-Pentane Acetone (1:1) 
(1:1) 
- N Methanol/Acetonitrile (1:2) 
■ “ Water 
y = yO + A*exp(R0*x) 
R 2 = 0.99 
Oligomer release 
- Exponential fit 
Swelling [%] 
Fig. 2 Release of oligomers as a function of swelling for different 
organic solvents (water, methanol/acetonitrile, methanol/pentane, 
acetone, hexane, hexane/acetone, dichloromethane/acetone, 
ethylacetate) using ASE (100 °C, 2x10 min)