Solid phase microextraction, or SPME, is a

solid phase extraction Solid-phase extraction (SPE) is a solid-liquid extractive technique, by which compounds that are dissolved or suspended in a liquid mixture are separated, isolated or purified, from other compounds in this mixture, according to their physical and ...

sampling technique that involves the use of a fiber coated with an extracting phase, that can be a liquid (

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

) or a solid (

sorbent A sorbent is an insoluble material that either absorbs or adsorbs liquids or gases. They are frequently used to remove pollutants and in the cleanup of chemical accidents and oil spills. Besides their uses in industry, sorbents are used in comm ...

), which extracts different kinds of

analyte An analyte, component (in clinical chemistry), titrand (in titrations), or chemical species is a substance or chemical constituent that is of interest in an analytical procedure. The remainder of the sample is called the matrix. The procedure ...

s (including both volatile and non-volatile) from different kinds of media, that can be in liquid or gas phase. The quantity of analyte extracted by the fibre is proportional to its concentration in the sample as long as

equilibrium Equilibrium may refer to: Film and television * ''Equilibrium'' (film), a 2002 science fiction film * '' The Story of Three Loves'', also known as ''Equilibrium'', a 1953 romantic anthology film * "Equilibrium" (''seaQuest 2032'') * ''Equilibr ...

is reached or, in case of short time pre-equilibrium, with help of

convection Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...

or agitation.

Analysis

After extraction, the SPME fiber is transferred to the injection port of separating instruments, such as a

gas chromatography Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for Separation process, separating and analyzing compounds that can be vaporized without Chemical decomposition, decomposition. Typical uses of GC include t ...

and

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used ...

, where

desorption Desorption is the physical process where Adsorption, adsorbed atoms or molecules are released from a surface into the surrounding vacuum or fluid. This occurs when a molecule gains enough energy to overcome the activation barrier and the binding e ...

of the analyte takes place and analysis is carried out.

Advantages

The attraction of SPME is that the extraction is fast, simple, can be done usually without solvents, and detection limits can reach parts per trillion (ppt) levels for certain compounds. SPME also has great potential for field applications; on-site sampling can be done even by nonscientists without the need to have gas chromatography-mass spectrometry equipment at each location. When properly stored, samples can be analyzed days later in the laboratory without significant loss of volatiles.

Fiber Coatings

The coating on the SPME fiber can be selected to improve sensitivity for specific analytes of interest; ideally the sorbent layer will have a high affinity for the target analytes. There are many commercially available SPME fiber coatings that are combinations of

polydimethylsiloxane Polydimethylsiloxane (PDMS), also known as dimethylpolysiloxane or dimethicone, is a silicone polymer with a wide variety of uses, from cosmetics to industrial lubrication and passive daytime radiative cooling. PDMS is particularly known for its ...

divinylbenzene Divinylbenzene (DVB) is an organic compound with the chemical formula and structure (a benzene ring with two vinyl groups as substituents). It is related to styrene (vinylbenzene, ) by the addition of a second vinyl group.CRC Handbook of Chemi ...

, Carboxen,

polyacrylate An acrylate polymer (also known as acrylic or polyacrylate) is any of a group of polymers prepared from acrylate monomers. These plastics are noted for their transparency, resistance to breakage, and elasticity. Acrylate polymer is commonly used ...

, and

polyethylene glycol Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular wei ...

. However, one downside to many of the commercially available SPME fibers is that they tend to be physically brittle due to their composition. Depending on the characteristics of the target analytes, certain properties of the coating improve extraction such as polarity, thickness, and surface area. The sample matrix can also influence the fiber coating selection. Based on the sample and analytes of interest, the fiber may need to tolerate direct immersion as opposed to a

headspace Headspace may refer to: Science and technology * Headspace gas chromatography, a technique in analytical chemistry * Headspace or ullage, the unfilled space in a container * Headspace technology, the gaseous constituents of a closed space abo ...

extraction. In one of the study the fiber coating method significantly enhances the performance of SPME by ensuring a high binding capacity and improved mass transfer efficiency. By preventing the ingress of the polymeric adhesive matrix into the pores of the sorbent particles, the method allows for faster adsorption and desorption times, which is crucial for high-throughput applications.

Application of SPME in Forensic Science

SPME has become an essential technique in forensic science, particularly for analyzing complex matrices such as blood, urine, and environmental samples. Its advantages include the ability to perform rapid and sensitive extractions without the need for extensive sample preparation, which is crucial in forensic investigations where sample integrity is paramount. For instance, SPME has been successfully employed to detect drugs of abuse, explosives, and other volatile compounds from various samples, allowing for the efficient identification of substances relevant to criminal cases. The automation and miniaturization of SPME techniques further enhance their applicability in forensic settings, enabling high-throughput analysis and reducing the risk of contamination.

Green Sample Preparation

SPME is recognized as a green analytical method for sample preparation, particularly in forensic drug analysis. This technique offers several advantages over traditional methods like liquid-liquid extraction (LLE) and solid-phase extraction (SPE), including automation, rapid sample processing, and reduced solvent usage. SPME allows for the extraction of analytes directly from complex matrices, such as biological and environmental samples, while minimizing the environmental impact associated with conventional extraction techniques.

References

Interactive lectures

Introduction to Solid Phase Microextraction

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