Microextraction by packed sorbent coupled with gas chromatography-mass spectrometry: a comparison between "draw-eject" and "extract-discard" methods under equilibrium conditions for the determination of polycyclic aromatic hydrocarbons in water

In this work, two different extraction procedures for the analysis of different polycyclic aromatic hydrocarbons (PAHs) in water by microextraction by packed sorbent (MEPS) have been compared in terms of sensitivity, reliability and time of analysis. The first method, called "draw-eject", consists of a sequence of cycles of aspirations and injections in the same vial; the second one, called "extract-discard", consists of a similar cycle sequence, but the aspired sample in this case is discarded into waste. The relevant partition equilibriums and extraction rates have been calculated by multivariate regression from the data obtained after MEPS gas chromatography-mass spectrometry (MEPS-GC-MS) analysis of 16 PAHs from water samples. Partitioning parameters for a priori prediction of solute sorption equilibrium, recoveries and preconcentration effects in aqueous and solvent systems have been calculated and compared for the two extraction procedures. Finally, real samples from sea, agricultural irrigation wells, streams and tap water were analyzed. Detection (S/N≥3) and quantification (S/N≥10) limits were calculated for the extraction processes. Under the experimental conditions used for the "draw-eject" procedure, these values were in the range 0.5-2 ng L(-1) and 1.6-6.2 ng L(-1), while for the "extract-discard" procedure they ranged from 0.2 to 0.8 ng L(-1) and from 0.8 to 2.0 ng L(-1), respectively.