Two extraction techniques that avoid solvent consumption and cut down the sample preparation to a minimum – Solid Phase MicroExtraction (SPME) and Stir Bar Sorptive Extraction (SBSE) – were compared on the basis of their reproducibility and sensitivity for 16 US EPA PAH compounds.
For the comparison of both techniques, water samples spiked with 10 ppt to 4 ppb of PAHs and a NIST Standard Reference Material were used as model systems. For SBSE reproducibilities at 100 ppt (in water) were found to be in the range of 4 to 15 % for compounds from naphthalene to benzo[a]pyrene and between 18 and 28 % for indeno[1,2,3]pyrene, dibenz[a,h]anthracene and benzo[g,h,i]perylene. For SPME reproducibilities at 2 ppb were in the range of 7 to 15 % for compounds from naphthalene to pyrene and between 38 and up to 79 % for the higher boiling compounds. Both techniques showed good linearity for four-point calibrations. Detection limits were calculated to be in the range from 0.08 to 2 ppt for SBSE and 0.3 to 84 ppt for SPME. Theoretical calculations indicated nearly quantitative recovery of all compounds under consideration except naphthalene for SBSE (10 mm GERSTEL TWISTER, df = 0.5 mm) whereas for SPME (100 μm PDMS) only higher boiling compounds benz[a]anthracene to benzo[g,h,i]perylene will show quantitative recovery and naphthalene for example will show only 10 % recovery.
The analysis of PAHs by SPME has certain limitations due to carry-over when using the 100 μm PDMS fiber. This problem is not encountered when using SBSE since we used multiple TWISTERs in parallel instead of using one TWISTER again and again. So far we did not test the behavior of TWISTER when running several samples one after another on the same stir bar.
First experiments with soil samples that contain a complex matrix indicated that both techniques can probably be used adequately for this analysis although the SPME technique showed too low sensitivity to quantitate the PAHs. This is most likely due to the fact that our very simple approach was insufficient to completely extract the PAHs from the soil into the liquid phase.
