Variables affecting SPME

The variables that influence SPME performance can be classified according to whether they relate to the retention step or the desorption step. 

Direct SPME Routine In situ chemical derivatization In situ redox reaction Most compounds Polar compounds Inorganic ions Gaseous and liquid 

Headspace SPME Routine Heating/cooling In situ chemical derivatization Volatile and semivolatile compounds Volatile and semivolatile compounds with small partition coefficients Polar compounds Any 

Testing of various types of needles has revealed good manufacturer control of the stationary phase thickness that results in good reproducibility (3-9% as RSD) [211]. The repeatability of extraction with the same fibre depends on phase thickness and is better with thicker phases, but is adversely affected by stirring (particularly when extracting by hand). 

One recent development in this context is an HPLC stationary phase of 5 pm particle size glued to the metal needle. Silica, and C reversed phases have been tested for 

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The variables that affect SBSE extraction performance are similar to the ones affecting SPME, namely, extraction time, extraction temperature (mainly for headspace mode, it should be noted however that the sorption process on the PDMS coating is not favored at high temperatures), selection of modifiers to increase the extraction efficiency (sueh as small amounts of organic solvents or high contents of salts), pH, stirring, and sample volume. 

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