Recovery experiments on solvents: Since it was observed that ethyl acetate lead to unusually high recoveries of some polyfluorinated compounds, different solvents (acetone, toluene, MTBE, DCM, butanone, acetone:petroleum ether 1:1 (v:v), and THF) were applied and evaluated in addition to ethyl acetate (Picograde and SupraSolv). The solvents were chosen because of similar polarity compared to ethyl acetate, their use in literature, and/or general laboratory use for semi-polar compounds. 100 µL of a standard solution containing 4:2 FTOH, 6:2 FTOH, 8:2 FTOH, 10:2 FTOH, 12:2 FTOH, 6:2 FTA, 8:2 FTA, 10:2 FTA, 7:1 FA, 9:1 FA, 11:1 FA, 13:1 FA, MeFOSE, EtFOSE, MeFOSA, EtFOSA, MeFBSA, MeFBSE, and Me2FOSA in ethyl acetate were spiked at two concentration levels (100 pg µL
-1, 500 pg µL-1) to 50 mL of each solvent. The solvents were firstly evaporated to about 1 mL using rotary evaporators and then to 200 µL using a gentle stream of nitrogen. Fifty µL of HCB (500 pg µL-1) were added as injection standard prior to the measurement to correct for volume differences. In addition to these experiments, 100 µL of the analyte standard solution, at the same two concentration levels, and 50 µL of HCB were added to 100 µL of each solvent directly within the vial. All experiments were performed in triplicate.
Extraction experiments: To evaluate the extraction efficiency of three pre-selected solvents (acetone, MTBE, and DCM) in comparison to ethyl acetate, glass cartridges (Orbo Tubes 6000 Supelco, Munich, Germany) industrially filled with 25 g XAD-2 between two 6 cm polyurethane foam (PUF) plugs, were spiked with 50 µL of a standard solution containing 4:2 FTOH, 6:2 FTOH, 8:2 FTOH, 10:2 FTOH, 12:2 FTOH, 6:2 FTA, 8:2 FTA, 10:2 FTA, MeFOSE, EtFOSE, MeFOSA, EtFOSA, MeFBSA, MeFBSE, Me2FOSA, and PFOSA (200 pg µL-1). As internal standard 50 µL of a solution containing 13C 6:2 FTOH,
13C 8:2 FTOH, 13C 10:2 FTOH, D3 MeFOSA, D5 EtFOSA, D7 MeFOSE, and D9 MeFOSE (200 pg µL-1) were added. Solvent was filled into the cartridges until the entire sandwhich was covered with solvent. For the extraction, the solvent was allowed to soak for 1 hour (first
STUDY 1 EXPERIMENTAL
extraction) and ½ hour (second extraction). After each extraction step, the remaining solvent in the cartridge was blown out using nitrogen. All cartridges were extracted twice and the solvent (approximately 350 mL) was evaporated with ethyl acetate as keeper to 150 µL using rotary evaporators and nitrogen. Fifty µL of the injection standard containing TCB D3 and
13C HCB (500 pg µL-1) were added prior to the measurement to correct for volume differences. Experiments were performed in triplicate.
Confirmation of the quality of the chosen extraction solvent: Since it turned out that a mixture of acetone and MTBE might be a suitable alternative to ethyl acetate, 50 mL MTBE:acetone 1:1 (v:v) and two PUF/XAD-2/PUF cartridges were spiked with 50 µL of a standard solution containing 4:2 FTOH, 6:2 FTOH, 8:2 FTOH, 10:2 FTOH, 12:2 FTOH, 6:2 FTA, 8:2 FTA, 10:2 FTA, MeFOSE, EtFOSE, MeFOSA, EtFOSA, MeFBSA, MeFBSE, Me2FOSA, and PFOSA (200 pg µL-1). Additionally the method was applied to two real samples which were collected at a site close to Hamburg within 3 days in June 2006 using high volume air samplers (about 1500 m³. 50 µL of the solution containing 13C 6:2 FTOH, 13C 8:2 FTOH,
13C 10:2 FTOH, D3 MeFOSA, D5 EtFOSA, D7 MeFOSE, and D9 MeFOSE (200 pg µL-1) were added to all samples for correction of analyte recoveries. All cartridges were extracted twice with MTBE:acetone 1:1 (v:v) as described above. The solvent was evaporated with ethyl acetate as keeper to 150 µL using rotary evaporators and nitrogen. Fifty µL of the injection standard containing TCB D3 and 13C HCB (500 pg µL-1) were added prior to the measurement to correct for volume differences.
2.3. Instrumental Analysis & Quantification
Quantification was performed by gas chromatography-mass spectrometry with positive chemical ionization (PCI) using the selected ion monitoring (SIM) mode. For confirmation, samples were also run in negative chemical ionization (NCI) mode. The 6890 GC (Agilent Technologies, Waldbronn, Germany) was equipped with a PTV inlet and coupled to a 5975 inert MS (Agilent Technologies, Waldbronn, Germany). The following previously optimized instrumental conditions were used: injection volume: 2 µL; injection mode: pulsed splitless;
pulse pressure: 40 psi, initial inlet temperature 60 °C hold for 0.10 min; heating rate:
400 °C min-1 to 270 °C hold for 20.00 min; oven temperature program: initial oven temperature 50 °C hold for 2 min, 3 °C min-1 to 70 °C hold for 0 min, 10.00 °C min-1 to 130 °C hold for 0 min, 20 °C min-1 to 220 °C hold for 0 min, 120 °C min-1 to 275 °C hold for 5 min, 10 °C min-1 to 270 °C hold for 10 min; transferline temperature: 250 °C; column flow:
EXPERIMENTAL STUDY 1
quadrupole temperature (PCI) 150 °C; ion source temperature (NCI): 150 °C; quadrupole temperature (NCI) 150 °C. The capillary column was thoroughly chosen in separate experiments (also see supplemental information), finally analytes were separated on a Supelcowax10 (Supelco, Munich, Germany) capillary column, 0.25 mm i.d., 0.25 µm film thickness, 60 m and 30 m for the evaluation of pure solvents, 60 m for the remaining experiments.
Recoveries of analytes spiked to 50 mL of pure solvents were calculated using standard solutions of the equal concentration levels in the same solvent. For quality assurance a five point calibration was measured with each set of solvent and used for control calculations of evaporated and not evaporated samples.
Quantification was based on peak areas. Analyte concentrations in the extraction experiments were calculated using a seven point calibration. Internal standards were used to correct for analyte losses. Based on the signal to noise ratio, the limit of detection was between 0.2 pg (various analytes) and 8.2 pg (PFOSA), the limit of quantification was between 0.4 pg (various analytes) and 16.4 pg (PFOSA, also see supplemental information).
2.4. Quality Assurance & Quality Control
All experiments were performed in a clean lab (class 10.000). Perfluorinated materials or fluorinated polymers were avoided. Silicon-Teflon septa were used for measurements (vials), however, extensive pre-tests showed no contamination with (semi-)volatile polyfluorinated compounds. The glassware was machine-washed, heated at 250 °C for twelve hours, and washed with the used solvent before use. Standard solutions were only used at room temperature. If not mentioned differently, mass-labeled injection standards and internal standards were used to correct for losses and irregularities during analysis and measurement.
For each compound, one target ion (PCI) and one qualifier ion (PCI and/or NCI) were measured for the GC-MS identification of the compounds. If not mentioned differently, a seven point calibration was run with each set of samples measured. Linearity of the GC-MS measurements was determined as described in DIN 32645 (1994). Blank samples were measured to determine possible cross contamination of the entire method. No signals were found.
STUDY 1 RESULTS &DISCUSSION
3. Results & Discussion