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).