Polydimethylsiloxane extraction, polar volatiles

As indicated above the fiber coatings can range from a rather nonpolar polydimethyl-siloxane to the more polar polyacrylate film. The polydimethylsiloxane phase is used for the determination of nonpolar volatile compounds in water samples [174,175]. In comparison, the polyacrylate fiber is preferred for the extraction of more polar compoimds. The first application of SPME to the analysis of polar compounds was the determination of phenols performed by Buchholz and Pawlisz)m [176]. These authors reported a detection limit at the ng/L level for the GC/FID and GC/MS procedures using a saturated sodium chloride solution at pH 4 to increase the SPME sensitivity. In connection with... 

To carry out the analysis of PAHs by SPME-DED, the DED was introduced into the core of solid gelatines and thereafter, the needle of the SPME holder was placed into the DED. Once inside the solid material, the fibre was exposed to the small space inside the DED, which has small holes that allow the volatiles from the sample to enter into the space in which the fibre is kept. Figure 1 shows the DED, the way in which it is coupled to SPME, and how SPME-DED is used to extract PAHs from gelatines. The used SPME fibre was that made up of polydimethylsiloxane (PDMS 100 pm). PDMS is a liquid and non-polar polymer that is commonly used in the extraction of PAHs due to the non-polar nature of these compounds. However, since there are a variety of stationary phases for SPME fibres, we previously carried out the selection of the most appropriate SPME fibre for PAHs analysis (Martin and Ruiz, 2007). In such study, different SPME fibres were evaluated (PDMS 100 pm divinylbenzene/polydimethylsiloxane 65 pm and polyacrilate 85pm). The three SPME fibres showed good and similar efficacy, reproducibility, linearity and limit of detection for extraction of PAHs by SPME-DED, but PDMS stand out from the others because its better results for most studied PAHs and other desirable characteristics like its higher resistance or lower conditioning time. Extractions were carried out at 25°C for 60 min. 

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