The need for greater efficiency in the preparation of samples has already started to stimulate the search for combinations of extraction processes to revolutionize the production and research and development sector in the public and private environment. Conventional techniques such as solid phase extraction (SPE), liquid-liquid extraction (LLE) can be well combined with some microextraction techniques such as solid phase microextraction (SPME) and dispersive liquid-liquid microextraction (DLLME), while, taken individually they have advantages and limitations.
Innovative strategies such as combining different methods serve to limit the problems related to complex matrices such as environmental ones (soil, water, air, etc.), food products and biological samples.
The main objective is to optimize separation, enrichment and purification of analytes. The overall improvement of the analysis is achieved through the synergistic approach which allows the isolation of compounds even in traces and very low concentrations, fundamental for accurate and sensitive detection.
Technological advances are driving the demand for protocols for more efficient and reliable analytical methods. Indeed, these hybrid techniques are not only designed to meet specific extraction requirements, but also to simplify and reduce the number of steps in analytical work, especially by reducing the use of solvents and decreasing the need for specialized equipment.
Why Combining Extraction Processes?
Combining extraction processes is driven by several compelling reasons that address the inherent challenges and limitations of individual extraction methods. One of the primary motivations is the need to handle complex matrices effectively. Traditional extraction techniques often struggle with samples that contain multiple interfering substances. For example, by combining methods such as SPE with Dispersive Liquid-Liquid MicroExtraction of UAE with µ-SPE , better separation and purification can be achieved during laboratory analyses, thus improving purity and increasing concentration.
MAE in combination with simultaneous Liquid-Phase Micro Extraction (LPME) can ensure maceration and extraction in a single step, optimizing time and costs. This not only increases operational efficiency but is intended to be in line with the principles of green chemistry, reducing waste and energy consumption to a minimum.
The flexibility offered by combined methods allows for customization to specific analytical needs. Whether solid or liquid samples, extractors can select the appropriate combinations that best suit the nature of their samples and the analytes of interest.
Combining Extraction Processes for Solid Samples
Combining extraction processes for solid samples is a highly effective strategy for improving analyte recovery, selectivity, and overall analytical performance. Solid samples often present challenges due to their complex matrices and difficulty accessing target compounds. Traditional methods alone may not be sufficient to achieve the desired levels of efficiency and sensitivity.
By integrating techniques such as microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE) with microextraction methods, results can be significantly improved, responding to market demands. Technologies based on microextraction exploit small quantities of solvents and materials, in line with the principles of green chemistry. Miniaturizing the process means increasing extraction efficiency and reducing environmental impact. The analyzes can also be automated and coupled with further advanced analytical tools (HPLC, GC, MS).
If you integrate technologies like the MAE or UAE with microextraction you can notice improvements in the quality of extraction, let’s see some examples.
MAE combined with Microextraction
MAE, which uses microwave energy to rapidly heat the solvent, increases the transfer speed of the analytes into solution, with evident time savings. This method is particularly advantageous for solid samples that require the disruption of strong intermolecular forces to release target analytes. One of the main advantages of this combination is the significant increase in extraction yields.
MAE’s efficient heating mechanism ensures that a greater proportion of target compounds are transferred from the solid sample to the extraction solvent. This is particularly useful for extracting thermally stable compounds from plant materials, soil and food samples, where traditional methods may prove lacking.
If microextraction techniques such as SPME or Liquid-Phase Microextraction are combined, the process benefits from high enrichment factors due to MAE and the specificity offered by these miniaturized methods.
UAE combined with Microextraction
Researchers also use ultrasound-assisted extraction techniques (UAE) because this technology takes advantage of the production of cavitation bubbles induced by a device equipped with a probe (called sonotrope) which is immersed in the solution. Ultrasounds are generated by means of piezoelectric materials such as quartz or barium titanate: the frequency, the power of the generated waves and the type of propagation in the materials vary based on the material chosen.
Ultrasound facilitates the release of analytes from the solid matrix into the solvent by stimulating the rupture of membranes or cell walls through the implosion of bubbles near the surfaces of the solid creating microjets at very high temperatures and pressures, while microextraction allows selective extraction of compounds based on chemical characteristics. This synergy leads to extracts with reduced contamination or co-extracted impurities with considerable time savings.
When UAE is combined with microextraction methods such as SPME or DLLME there are multiple advantages. The mechanical action of UAE guarantees complete extraction of analytes, even those deeply embedded in complex matrices.
The microextraction technique concentrates these analytes into a smaller volume, improving the detection limits and sensitivity of the assay. An advantage of this combination is the improvement in yield. The ability of UAE to break down solid/complex matrices more effectively than conventional methods leads to higher recovery rates of target compounds. This is particularly advantageous for bioactive compounds in medicinal plants, pesticides in soil, and contaminants in food products, where achieving high yields is critical for accurate quantification. Selectivity is another significant advantage.
Combining Extraction Processes for Liquid Samples
One of the main disadvantages of extraction from liquid samples is the large variety of polarities of the analytes and the presence of interfering substances. Even in this case, the combination of extraction processes can represent a solution. In fact, traditional extraction methods such as LLE may not be sufficient to address these complexities.
By integrating advanced techniques such as SPE with microextraction methods, extractors can significantly improve the efficiency and effectiveness of the extraction process. One of the main advantages of combining extraction processes for liquid samples is the ability to achieve high enrichment and improved cleanliness.
For example, SPE-DLLME is a popular combination in which SPE serves to isolate and pre-concentrate target analytes from large volumes, while DLLME further improves the concentration of these analytes, leading to significantly improved detection sensitivity. This two-step approach ensures that even trace-level analytes can be accurately quantified.
SPE combined with Microextraction Techniques
The objective of combining techniques such as SPE with microextraction techniques such as DLLME or SPME is to improve the efficiency and selectivity of the extraction method applied to liquid samples. SPE is renowned for its ability to handle large volumes of liquid, offering robust cleanup and pre-concentration of analytes.
When combined with microextraction methods, the overall analytical performance is significantly enhanced, and the volumes of materials are reduced. Microextraction techniques typically use very small amounts of solvents, which complements the SPE process, making the overall extraction procedure more economical and environmentally friendly, reducing the environmental footprint of the extraction process.
One of the primary advantages of combining SPE with microextraction techniques is the substantial increase in enrichment in the analyte’s concentration.
SPE can efficiently isolate and concentrate target analytes from large liquid volumes, removing many interfering substances. The following application of microextraction methods like DLLME further concentrates the analytes into a much smaller volume, resulting in exceptionally high enrichment factors and improved sensitivity for trace-level detection.
The selectivity of the extraction process is also greatly improved through this combination. SPE cartridges can be tailored with specific sorbents to target particular classes of compounds, while microextraction methods add another layer of selectivity based on the physicochemical properties of the analytes. This dual selectivity ensures that the final extract is highly purified and free from many potential contaminants.
Summary of Combining Extraction Methods
The combination of extraction processes creates innovative solutions to overcome the limitations of individual methods. By integrating techniques such as MAE and UAE with microextraction methods like SPME and DLLME, extractors can achieve superior extraction yields, enhanced selectivity, and more efficient workflows.
For solid samples, the synergy between advanced extraction techniques and microextraction facilitates the thorough disruption of complex matrices, enabling the efficient release and concentration of target analytes. In liquid samples, combinations like SPE-DLLME provide enhanced cleanup and ultra-high enrichment factors, ensuring precise and sensitive detection of trace compounds.
While combined extraction methods offer numerous advantages, including reduced solvent usage, minimized procedural steps, and improved adherence to green chemistry principles, they also present challenges such as increased operational complexity and time. Future research should focus on addressing these challenges through the development of automated and online coupled extraction systems. Such advancements could streamline the analytical process, reduce the likelihood of human error, and further enhance the efficiency and reliability of combined extraction methods.
References:
- M. Sajid, J. Płotka-Wasylka, Combined extraction and microextraction techniques: recent trends and future perspectives. Trends in Analytical Chemistry. 2018.
