SPME Fiber Materials and Extraction Parameters

There are several stationary phases in use for SPME. Table 9.6 lists the most common stationary phases as well as their interaction mode. 

Besides the nature of the stationary phase, the thickness of the coating also plays a key role. The thickness varies from 100 pm downward to 7 pm. The thirmer the coating, the shorter the equilibration time needed. Depending on the volatility of the analytes, the SPME procedure can be optimized by choosing the appropriate stationary phase thickness. The more volatile the compound, the thicker the coating. Low-volatile compounds are extracted using a thin coating. 

Factors, other than the already mentioned, affecting the adsorption during SPME are pH, ionic strength, use of water and organic solvents, temperature, agitation, and time. 

Polydimethylsiloxane-divinylbenzene (PDMS-DVB) Nonpolar to moderate polar 

Best recoveries are obtained when the analytes are in their uncharged state. This means, as with the other extraction techniques discussed, that the pH of the sample should suppress ionization of basic and acidic compounds. Neutral compounds are not affected by pH. It should be noted that since SPME fibers can be reused up to 100 times, it is important that the pH range of extraction should be within 2 and 10 (in case of immersion SPME). 

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