Solid-phase extraction in speciation analysis

SPE for speciation analysis
The SPE process is based on the selective distribution of analytes between the solid extraction material and liquid mobile phase. The analytes are transferred to the solid phase when they possess greater affinity for the solid phase than for the sample matrix. Once retained during the loading step, the analytes are recovered in a second step by elution using a suitable eluent or by thermal desorption into the gas phase. SPE can process large volumes of liquid samples in relatively short time in a reproducible manner.

photo: SPE station

Generally, there are several formats of SPE: SPE cartridges, SPE disks, SPE pipette tips and SPE microcolumns.  Commercial SPE cartridges, disks and pipette tips are widely used, but often operated in an manual off-line mode.

In contrast, the SPE microcolumn can easily be operated on-line coupled to compatible analytical techniques. The separation process can be tailored by selecting the solid phase from a variety of sorbents including reversed phase sorbents, normal phase sorbents, ion exchange sorbents to biological sorbents, carbon nanotubes, graphene, graphene oxide, metal–organic frameworks, mesoporous nanoparticles and functional magnetic nanoparticles, to name only some. Since the interactions between sorbents used for commercial cartridges and target species are not specific, these are most often used for sample clean-up rather than preconcentration of the species.

Speciation studies making use of SPE for species preconcentration and separation are often based on the development of sorbents designed to interact with a given group of species. Strategies to obtain high selectivity of sorbents are based on the use of ion/molecule imprinted materials, biological substrates or nanoparticles. Using nanoparticles as sorbents offers the possibility of surface functionalization for improved analyte selectivity.  

Miniaturization of SPE has been realized with the development of solid-phase micro-extraction (SPME) in the early 1990s. Beyond miniaturization, SPME integrates sampling, sample preparation, and preconcentration into a single step prior to instrumental analysis with special designed interfaces for  sample introduction. Compared to conventional SPE, SPME features many advantages such as simplicity, rapidity, convenience, and low sample/reagent consumption. Common formats of SPME include fibre SPME, in-tube SPME (also termed as CME), and stir bar sorptive extraction (SBSE).

SPE/SPME has been widely used in elemental speciation of biological, environmental and food samples because of their excellent matrix tolerance and high EF obtainable during short collection time. SPE is more suited for the analysis of large volume biological samples, while SPME, CME and SBSE are used with smaller volumes, less than 1 mL.

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Chapter 15: Liquid-liquid extraction in speciation analysis
Chapter 16: Solid-phase extraction in speciation analysis

Chapter 17: Mercury 'speciation analysis' by using thermal desorption analysis
Chapter 18: Multielement speciation analysis

Chapter 19: Chemical speciation modelling