Solid phase microextraction (SPME) is a revolutionary method in analytical chemistry that allows the extraction and concentration of volatile and semi-volatile compounds without the use of solvents.
Developed in the 1990s by Janusz Pawliszyn, this technique has transformed extraction processes, particularly in sectors such as food, cosmetics , and the environment. Due to its high sensitivity, versatility, and low environmental impact, SPME has become an essential tool in modern laboratories.
1. What is SPME?
A technical and historical definition
Solid-phase microextraction is an analytical technique that combines the extraction and concentration of analytes. It relies on the use of a fiber coated with a stationary phase capable of adsorbing trace chemical compounds present in liquid, solid, or gaseous matrices. Invented in the early 1990s, this technique is part of an effort to optimize analyses by eliminating the use of organic solvents, which are often costly and polluting.
Difference with traditional methods
Unlike liquid-liquid extraction methods, which require significant amounts of solvent to isolate analytes, SPME is a more environmentally friendly and cost-effective technique. Furthermore, it allows for complete automation, a key advantage for laboratories that need to handle large volumes of samples. These characteristics make SPME a preferred alternative for trace analysis, particularly in sectors where precision is critical.
The fundamental principles of the technique
The SPME is based on three main stages:
- Adsorption of analytes on the fiber : A fiber coated with a specific stationary phase is exposed to a sample, either by immersion in a solution, or in the headspace of a vial containing the sample.
- Establishment of equilibrium : After a defined exposure time, an equilibrium is established between the stationary phase and the sample matrix. This process allows for optimal adsorption of the analytes.
- Desorption and analysis : The fiber is then placed in a heated gas chromatography (GC) injector, where the analytes are thermally desorbed and transported to an analytical column for identification.
These steps, although simple in principle, require rigorous optimization to ensure efficient and reproducible extraction.
A technique suitable for multiple industries
The versatility of SPME allows its application in a variety of sectors. In the food industry, it is used to analyze terpenes and other volatile compounds present in essential oils, alcoholic beverages, and processed products. In cosmetics, it enables the detection of volatile allergens and the optimization of formulations. Finally, in the environmental field, it is commonly used to monitor air quality and detect volatile organic pollutants (VOCs).
This technique, at the crossroads of technological innovation and ecological concerns, is now becoming an indispensable tool to meet the requirements of modern analyses.
2. Why use the SPME
An environmentally friendly and economical technique
Solid-phase microextraction (SPME) stands out for its environmentally friendly approach. Unlike conventional methods, such as liquid-liquid extraction, which require the use of large quantities of organic solvents, SPME requires none. This reduces not only the costs associated with purchasing and disposing of solvents, but also their environmental impact.
This absence of solvents also eliminates the risk of sample contamination, thus ensuring greater purity of results. In laboratories, this approach contributes to a more sustainable transition, aligned with current requirements for reducing environmental footprint.
Increased sensitivity and versatility
SPME is particularly valued for its ability to detect trace compounds, with detection limits reaching levels of ng/L or µg/L , depending on the matrix analyzed. This exceptional sensitivity makes it a preferred tool for industries requiring high-precision analyses, such as food and cosmetics.
Furthermore, this technique is extremely versatile. It can be applied to a wide range of matrices, including:
- Liquid matrices (floral waters, alcoholic beverages, aqueous solutions).
- Solid matrices (food powders, plant extracts).
- Gaseous matrices (air analysis, headspace in packaging).
This flexibility allows it to be used for many applications, from laboratory quality control to research and development.
Automation for increased efficiency
One of the major advantages of the SPME is its compatibility with automated systems. Modern laboratories, often faced with an increasing number of samples to analyze, seek solutions that combine speed and reproducibility. The SPME meets these needs through its integration into automated sample changers.
These systems allow:
- The processing of long series of samples, sometimes up to 32 in a single sequence.
- Reducing human error through a standardized protocol.
- A significant time saving, with reduced analysis times.
Automation is particularly beneficial for laboratories performing routine analyses, where repeatability of results is essential.
Comparison with other extraction methods
Although SPME offers many advantages, it is useful to compare it with other extraction techniques to better understand its added value:
- Liquid-liquid extraction (LLE) : This traditional method requires solvents and additional steps to concentrate analytes, increasing costs and processing time.
- Stir Bar Sorptive Extraction (SBSE) : Although SBSE is effective for low detection limits, it lacks automation and remains expensive in terms of equipment.
- Microwave-assisted extraction : This technique is fast but less suitable for volatile compounds, which limits its application to certain matrices.
In summary, the SPME offers an excellent compromise between analytical performance, ease of use and respect for economic and environmental constraints.
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3. The main stages of the SPME
Sample preparation
Sample preparation is a crucial step to ensure efficient and reproducible extraction. Before extraction, the sample must be conditioned to optimize interactions between the analytes and the SPME fiber.
- Suitable materials : SPME is used on solid, liquid, or gaseous samples. For example, for solid matrices, a dilution or maceration step may be necessary to release volatile compounds.
- Thermostatic heating : Most analyses require controlled heating of the sample to release volatile analytes. This step, called thermostatic heating, ensures homogeneous extraction and improves the repeatability of results.
- pH adjustment : pH can influence the adsorption equilibrium for certain compounds, particularly acids and bases. For example, volatile amines are more efficiently extracted under slightly alkaline conditions.
Extraction and adsorption
Extraction is performed by exposing the SPME fiber to the sample. This step relies on two main modes, chosen according to the nature of the analytes and the matrix to be analyzed.
- Headspace :
- In this mode, the fiber is placed in the gaseous space above a liquid or solid.
- This mode is ideal for volatile compounds such as terpenes, aromas or volatile organic contaminants (VOCs).
- The headspace minimizes interference from non-volatile compounds present in the matrix.
- Direct immersion :
- The fiber is directly immersed in a liquid sample.
- This method is suitable for semi-volatile analytes or compounds present in aqueous solution, such as alcohols or phenols.
- To prevent any degradation or oxidation of the analytes, it is sometimes necessary to add stabilizing agents, such as a saline solution.
- Extraction time and temperature :
- These parameters must be optimized for each type of sample. Insufficient or excessive duration can affect the sensitivity of the method.
Establishing balance
During extraction, a dynamic equilibrium is established between the analytes present in the sample and those adsorbed by the SPME fiber. This equilibrium depends on several factors:
- The chemical nature of the analytes.
- The properties of the stationary phase used on the fiber.
- Extraction conditions (temperature, duration, pH).
For quantitative analyses, it is essential that the extraction reaches a reproducible equilibrium state. This ensures that the measured signals correspond to precise concentrations in the sample.
Desorption and analysis
Once extraction is complete, the SPME fiber is transferred to the injector of a chromatograph for the desorption phase. This step releases the analytes trapped on the fiber, delivering them to the analytical instrument.
- Thermal desorption in a gas chromatograph (GC) :
- The fiber is introduced into a heated injector (often at 250°C or more) to allow complete desorption of the analytes.
- The volatile compounds are then transported by a carrier gas (e.g. helium or nitrogen) to an analytical column for separation.
- Desorption in a high-performance liquid chromatograph (HPLC) :
- In this case, a liquid mobile phase elutes the analytes from the fiber.
- This mode is primarily used for non-volatile or thermolabile compounds.
- Optimization of injection parameters :
- The use of a split/splitless injector must be adjusted to avoid compound losses during desorption.
- The choice of liner (insert) is also critical to ensure efficient desorption and optimal separation in the analytical column.
Importance of optimizing the steps
Each step of SPME requires rigorous optimization to obtain reliable and reproducible results. Poorly balanced extraction or incomplete desorption can lead to analyte losses or biased results.
For example, in food and beverage applications, insufficient desorption time could underestimate volatile aroma concentrations. In environmental analyses, poor optimization could miss traces of critical pollutants.
These well-controlled steps make SPME a powerful and precise method, suitable for varied and demanding analytical needs.
4. Types of SPME fibers and their selection
The most common stationary phases
SPME fibers are coated with specific stationary phases that determine their ability to extract analytes. Each type of stationary phase is designed for specific applications based on the chemical properties of the compounds to be analyzed. The most commonly used phases are:
- PDMS (polydimethylsiloxane) :
- Nonpolar phase suitable for volatile compounds of low molecular weight (60–275 u).
- Main applications: hydrocarbons, light alcohols, and non-polar compounds present in food or environmental matrices.
- PA (polyacrylate) :
- Polar phase designed to extract polar analytes, such as high molecular weight acids or alcohols (80–300 u).
- Main applications: aqueous matrices, cosmetic products containing hydrophilic components.
- PDMS/DVB (polydimethylsiloxane-divinylbenzene) :
- Mixed phase combining nonpolar and polar properties.
- Suitable for semi-volatile and polar analytes (alcohol, amines).
- Main applications: analysis of perfumes, volatile allergens, or contaminants in the air.
- PDMS/Carboxen :
- Phase very sensitive to volatile compounds present in trace amounts (30–225 u).
- Main applications: air quality control, analysis of volatile organic compounds (VOCs).
- DVB/Carboxen on PDMS :
- Hybrid phase offering a wide range of applications (C3 to C20).
- Main applications: complex samples combining volatile and semi-volatile compounds.
Phase thickness and specific applications
The thickness of the stationary phase coating plays a key role in the sensitivity and specificity of the extraction. Here are some recommendations based on the properties of the analytes:
- 100 µm PDMS : Ideal for volatile compounds with low molecular weight.
- 85 µm polyacrylate : Recommended for polar analytes in aqueous matrices.
- 75 µm PDMS/Carboxen : Suitable for volatiles present in minute quantities.
- 50/30 µm DVB/Carboxen/PDMS : Suitable for general analyses requiring high versatility.
The SPME Arrow: a technological breakthrough
The SPME Arrow is an evolution of the classic SPME, offering superior adsorption capacity thanks to an increased surface area and volume.
- Main features :
- Larger fiber diameter (1.1 mm or 1.5 mm) compared to traditional SPME.
- Thicker stationary phase, increasing sensitivity and reducing detection limits.
- Compatibility with complex and demanding sample analyses.
- Specific applications :
- 1.1 mm fibers: Optimal for headspace analysis, such as the study of aromas in beverages or food.
- 1.5 mm fibers: Ideal for direct immersion analysis, especially for liquid matrices such as plant extracts.
- Advantages compared to SBSE (Stir Bar Sorptive Extraction) :
- Total automation is possible with systems like PAL.
- A wider choice of stationary phases, allowing for better customization of analyses.
- Cost reduction through automated processes and simplified preparation.
Selection criteria for choosing the right SME fiber
The choice of SPME fiber depends on several factors, including:
- Nature of the analytes :
- Volatile or semi-volatile compounds.
- Polar or nonpolar analytes.
- Sample matrix :
- Gases, liquids, or solids.
- Presence of potential interferences (e.g., oils or fats in food matrices).
- Objective of the analysis :
- Qualitative analyses to identify the compounds present.
- Quantitative analyses to measure specific concentrations.
Best practices for optimal use of fibers
To guarantee reliable and reproducible results, it is essential to follow certain precautions for use:
- Conditioning the fiber : Before each analysis, the fiber must be heated to eliminate residual contaminants.
- Respect the maximum temperature : A fiber heated beyond its limits can degrade, compromising the integrity of the results.
- Use a suitable insert : Opt for a liner without glass wool to avoid interference and ensure optimal desorption.
- Adjusting injection parameters : The split ratio and desorption time must be adapted to each type of sample.
5. Analytical Applications of SPME
A technique suitable for many sectors
Solid-phase microextraction is a versatile method that can be integrated into a variety of analytical processes. Its ability to extract and concentrate volatile and semi-volatile analytes makes it an essential tool in several industries, including food and beverage, cosmetics, and environmental science.
Analysis in the agri-food sector
- Identification of aromas and terpenes :
- SPME is commonly used to analyze volatile compounds responsible for aromas and flavors in food and beverages.
- Examples of applications:
- Analysis of terpenes in essential oils (mint, lavender, lemon).
- Study of aromatic profiles in wine, coffee, or chocolate.
- Importance: These analyses allow for the optimization of formulations and ensure product quality.
- Contaminant detection :
- SPME makes it possible to identify undesirable residues, such as pesticides, mycotoxins, or volatile organic compounds (VOCs) present in food.
- Example: The detection of traces of contaminants in fruit juices or processed meats, ensuring compliance with food safety standards.
- Beverage Analysis :
- In the brewing industry, SPME is used to analyze the volatile profiles of hops and their interactions in beer.
- Concrete example: The development of specific sensory profiles in craft beers through in-depth analysis of volatile compounds.
Applications in cosmetics
- Detection of volatile allergens :
- SPME is used to analyze the volatile components of perfumes and creams in order to identify potential allergens.
- Example: Detection of compounds such as limonene or linalool, which are common allergens in cosmetic formulations.
- Formulation optimization :
- The analyses make it possible to assess the stability of perfumes and aromas in cosmetic products over time.
- Example: Study of the volatility of perfumes in moisturizing creams or body lotions.
- Migration test for packaging :
- Cosmetic products are often stored in plastic or metal packaging. SPME allows for the assessment of the potential migration of substances from the packaging into the product.
- Compliance with EC Regulation No. 1935/2004 to guarantee consumer safety.
Environmental monitoring
- Air quality analysis :
- SPME is a key technique for monitoring air pollutants, such as VOCs or polycyclic aromatic hydrocarbons (PAHs).
- Example: Analysis of industrial emissions to assess their impact on air quality.
- Water quality control :
- The method makes it possible to detect volatile contaminants in drinking water or industrial effluents.
- Example: Detection of traces of organic solvents in wastewater, contributing to pollution control efforts.
- Soil analysis :
- SPME can be used to extract volatile residues from contaminated soils.
- Example: Detection of petrochemical compounds or chlorinated solvents in industrial sites.
Case study: hops and beer
- Aroma profiling in hops :
- SPME has been used to analyze more than 150 varieties of hops, revealing the diversity of aromatic compounds they contain.
- Importance: These analyses have made it possible to develop craft beers with specific aromatic profiles, thus optimizing their appeal to consumers.
- Analysis of interactions in beer :
- By studying the interactions between hops and other ingredients, SPME helps to predict the evolution of aromas during brewing or storage.
- Example: Identification of the compounds responsible for the pine, citrus, or resin aromas characteristic of certain beers.
Impact on research and development
The analytical capabilities of the SPME make it an indispensable tool in research and development projects. Its role is particularly significant in:
- The development of new formulations (e.g., cosmetic products, beverages).
- Optimizing manufacturing processes (e.g., controlling aromas in food products).
- Quality assurance, guaranteeing products that meet consumer expectations and regulations.
6. Scientific dimension and laboratory analysis
Complementary techniques used with SPME
Solid phase microextraction integrates perfectly into various laboratory analysis protocols, often in combination with advanced techniques to ensure complete characterization of samples.
- Gas chromatography coupled with mass spectrometry (GC/MS) :
- SPME is particularly effective when combined with GC/MS, an ideal method for separating and identifying volatile and semi-volatile compounds.
- Advantages : High sensitivity, precise identification through mass spectrometry, and rapid analysis.
- Example application : Analysis of terpenes in essential oils to ensure product quality and conformity.
- High-performance liquid chromatography (HPLC) :
- Although SPME is often associated with GC, it can also be used with HPLC to analyze non-volatile or thermolabile compounds.
- Advantages : Ability to analyze polar or ionized analytes not suitable for GC/MS.
- Example of application : Dosage of active compounds in cosmetic or nutraceutical products.
- Coupling with IR or UV-Vis spectroscopy :
- The desorption of analytes extracted by SPME can be monitored by spectroscopic techniques to obtain additional information on their chemical structure.
- Example of application : Analysis of natural pigments in food products or additives in cosmetics.
Rheological tests and chemical interactions
Although SPME is primarily used to extract and analyze volatile compounds, it can also play an indirect role in studying the chemical interactions and physical properties of samples.
- Analysis of chemical interactions :
- In complex products, such as cosmetics or food formulations, SPME can be used to study the interactions between volatile compounds and the matrix.
- Example: Study of the evaporation of perfumes in a hand cream as a function of temperature or pH.
- Rheological tests :
- The physical properties of food or cosmetic matrices, such as their texture or stability, often influence the release of volatile compounds.
- Example: Measuring the texture of a sauce or emulsion after analyzing the aromas extracted by SPME.
- Formulation optimization :
- The results obtained with SPME can guide formulation adjustments to improve product quality.
- Example: Reducing flavor loss in long-term stored beverages through additive optimization.
7. YesWeLab and the SPME
YesWeLab's expertise in SME analysis
YesWeLab, with its network of over 200 partner laboratories, has positioned itself as a major player in the field of SPME analysis. Thanks to its expertise, YesWeLab offers solutions tailored to the specific needs of the food, cosmetics, environmental, and many other industries.
- Extensive analytical capabilities :
- Identification and quantification of volatile and semi-volatile compounds in various matrices.
- Development of customized protocols for specific analyses.
- Strategic partnerships :
- Collaboration with laboratories equipped with the latest technologies in SPME and GC/MS.
- Access to a rich database of several thousand compounds identified by SPME.
- Optimizing results :
- Use of validated and reproducible protocols.
- Technical support to help companies interpret results and optimize their processes.
Concrete examples: applications of the SPME with YesWeLab
YesWeLab has demonstrated the effectiveness of SPME in several complex analytical projects, helping to improve products and ensure their regulatory compliance.
- Aroma analysis in essential oils :
- Objective: To identify volatile and semi-volatile terpenes to guarantee the quality of essential oils.
- Result: Accurate detection of key components such as limonene, linalool, and pinene, allowing validation of the authenticity and purity of the products.
- Quality control in the agri-food industry :
- Objective: To detect volatile contaminants in food matrices, such as fruit juices and processed products.
- Result: Identification of traces of pesticides and other undesirable compounds, ensuring compliance with European standards.
- Study of migrations in packaging :
- Objective: To test materials in contact with food to ensure they do not release toxic substances.
- Result: Detailed analysis of specific migrations according to EC Regulation No. 1935/2004, enabling improvements in packaging formulations.
Services offered by YesWeLab in connection with the SPME
To meet the diverse needs of its clients, YesWeLab offers a full range of services based on SME, adapted to different industrial sectors.
- Development of customized protocols :
- Creation of customized analytical methods to meet the specific requirements of the products.
- Examples: Complex aroma analysis, allergen testing in perfumes.
- Regulatory support :
- Support to ensure compliance with European (EC No. 1935/2004, INCO, etc.) and international (FDA) standards.
- Assistance in preparing approval or certification files.
- Analysis and interpretation of results :
- Provision of detailed reports and interpretation of analytical data.
- Recommendations for optimizing formulations or improving production processes.
The advantage of the YesWeLab platform
YesWeLab stands out for its digital platform, designed to simplify the analysis process and offer a seamless experience to its clients.
- Centralization of analytical needs :
- Access to an online catalogue of over 10,000 analyses, including advanced options for SMEs.
- Simplification of the process, from ordering to receiving results.
- Traceability and transparency :
- Real-time tracking of samples, from shipment to obtaining results.
- Detailed history of analyses to facilitate data management.
- Reduction of execution times :
- Collaboration with certified laboratories for optimal turnaround times.
- Automation of analytical processes using state-of-the-art equipment.
The benefits of working with YesWeLab
- A network of experts :
- Access to diverse expertise covering all analytical needs.
- Ability to handle complex requests thanks to advanced technologies such as SPME.
- Flexibility and customization :
- Adapting services to the specific needs of each project.
- Tailor-made options for industries requiring in-depth analysis.
- Regulatory compliance assured :
- Analyses aligned with ISO standards and sector-specific requirements.
- Guarantee of reliable results accepted by certification authorities
