Solid Phase Microextraction (SPME) is an extraction process for both volatile and semi volatile compounds in preparation for GC or HPLC analysis. One of the major benefits of SPME is that by choosing the proper extracting phase coated on a SPME fiber, target analytes can be extracted leaving unwanted compounds behind in the matrix. This makes SPME very popular in applications where the resulting chromatograms are complex, with many different types of compounds (link to SPME application notes). Maybe an analyst wants to see polar compounds that are typically related to a food’s taste or smell. A polar extraction phase can be chosen to target these compounds, resulting in a simpler and easier chromatogram. Since the extraction uses no solvent, part per trillion (ppt) detection levels are possible and an analyst would not come in contact with potentially dangerous solvents during the analysis.

SPME is performed with a SPME fiber. The fiber is coated with a liquid phase polymer and/or a solid sorbent and is mounted within a needle. There are many different phases available and choosing the correct fiber that is optimal for your analysis is part of the method development process. Some systems, such as the Flex Autosampler, have automated fiber exchange systems (MFX) where multiple fibers can be run in a single sequence. The fiber can be extended out of the needle during extraction or desorption, but retracted inside the needle when the needle needs to pass through septa.

The steps involved in SPME are different depending upon whether you are targeting volatile or semi volatile compounds. For volatiles, the sample is typically placed in a 20ml headspace vial and the sample is heated until the analytes come to equilibrium (For more information about headspace, visit our What is Headspace? page). The SPME needle punctures the vial septa and the fiber is extended into the headspace of the vial. Typically the vial is slowly mixed during this extraction step. Extraction times vary depending upon the analyte, fiber phase etc. and must be optimized as part of the method development. Due to the affinity of the selected fiber for the target analytes, these are absorbed onto the fiber. Once extraction is complete, the fiber is pulled back into the needle; the needle is placed into the injection port. The heat from the injection port and the carrier gas from the GC sweep the compounds off the fiber and into the GC column. The fiber can stay in the injection port, or be moved to a SPME fiber conditioning station to clean it before going onto the next sample.

For semi volatile samples the fiber is exposed directly in the liquid of the sample during extraction. For GC analysis, the fiber can be placed in the injection port and compounds will be swept into the GC. For HPLC analysis, the fiber can be placed into a vial containing a small amount of solvent, extracting the compounds off the fiber.

The Flex 2’s SPME (Solid Phase Microextraction) option is an excellent choice for labs who need a precise and accurate autosampler. The Flex 2 is Capable of both volatile and semi-volatile analysis, method development decisions include incubation time and temperature, extraction time, chromatographic conditions and most importantly SPME fiber type.