2.5 Quality control/quality assurance
Utmost care was taken to avoid contamination of sampling devices (stir
bars and PU foams) with PAHs. Blank runs were performed on cleaned SBSE
devices and pristine PU foam items and revealed PAH contents below
detection limits. Each sampling point in time and space was performed in
triplicate after preliminary SBSE runs had been performed to assess
suitable exposure periods. Transport of SBSE devices and sampling
filters from the sampling site to the laboratory was done with utmost
care to avoid contamination with PAHs. PAH recovery rates from the
polyurethane foam was determined by extraction of PU foam cartridges
fortified with solutions the 16 EPA PAH in toluene prepared from SRM
NIST SRM 1647f (1:10). After evaporation of the solvent the cartridges
were submitted to pressurized fluid extraction as described in section
2.4 either directly or after having rested for one to ensure compete
solvent evaporation. Peak areas for each PAH as determined form the
extracts and a solution of NIST SRM 1647f diluted in the extraction
solvent to simulate a 100% recovery were compared (see supplementary
Table S2). Linearity of the PAH recovery from the SBSE devices over the
relevant range was investigated by spiking cleaned devices with 1 µL of
solutions of NIST SRM 1647f diluted in toluene. The solvent was allowed
to evaporate at ambient temperature and after 1 h the SBSE device were
submitted to thermal desorptive extraction as described in section 2.4.
For amounts of substances spiked and coefficients of determination see
supplementary Table S3. Limits of detection and quantification were
determined by the linear regression method laid down in ISO
1184320 and implemented in the software package
DINTEST21 and it could be shown to reach at least
between 0.26 and 3.4 pg absolute per device depending on the PAH
congener, for details see supplementary Table S3. In order to estimate
the sorption capacity of PAHs a number of SBSE devices was incubated in
the headspace of charcoal. It was seen that all 16 PAH congener were
adsorbed to an extent far beyond the concentration range observed in
this work (data not shown).