Solidphase Microextraction Devices For Passive Sampling In Soil And Sediment

The SPME technique was first introduced by Pawliszyn et al. in 1990 [24]. Since then, the SPME technique has been widely applied to the sampling and analysis of environmental, food and pharmaceutical samples [25]. Nilsson et al. introduced an SPME device for in situ sampling of groundwater and soil gas [26]. In this device, the SPME fibre was protected with a cap and a number of holes were drilled into the cap for liquid exchange or gas flow. The analytes passed through the holes and were then extracted by the SPME fibre. This SPME device was placed in the headspace to monitor underground soil gas or was lowered into a well for direct groundwater sampling. Toluene and naphthalene were detected by underground soil gas sampling and their presence was confirmed by extractions using Tenax® tubes. This type of SPME device requires a sampling time that is long enough to reach equilibrium. The results obtained by this device are the concentrations of analytes at the time the samplers were retrieved, not the TWA concentrations of the analytes in the sampling period.

It has also been demonstrated that SPME can be used as a TWA passive sampling technique. SPME TWA passive samplers for air and water sampling have been developed by Pawliszyn et al. between 1999 and 2005 [27-29]. Such devices are referred to as fibre-in-needle SPME devices [29]. For these devices, the SPME fibre is retracted a known distance into its needle during the sampling period. Analyte molecules access the fibre coating only by means of diffusion through the static air or water gap between the opening and fibre coating. The face velocity of air or water across the needle opening will not affect the sampling, due to the extremely small inner diameter of the fibre needle. The mass uptake can therefore be predicted by Fick's law of diffusion. This type of SPME device was also designed for field sampling. Figure 17.1 illustrates an SPME diffusive sampler for air sampling designed by Chen and Pawliszyn [30] and then modified by Supelco Company. Figure 17.2

Fig. 17.1. Supelco® SPME TWA air sampler.

Fig. 17.1. Supelco® SPME TWA air sampler.

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