An Ecologically Sustainable Approach to Solid-Phase Microextraction Techniques Using Deep Eutectic Solvents

Deep eutectic solvents (DESs) have attracted significant attention as eco-friendly and sustainable alternatives to conventional, often toxic, organic solvents. They are easy to synthesize, and their tunable physicochemical properties enable their application in microextraction techniques for a wide range of analytes. However, some DESs may exhibit thermal instability, and their high viscosity or solubility can influence the extraction efficiency. Despite these limitations, in recent years, DESs have been successfully used in multiple roles in solid-phase microextraction (SPME). They may be used to functionalize or modify sorbent materials, thereby forming composite sorbents with enhanced performance. Moreover, DESs can be combined with polymers to produce hybrid materials with improved extraction capabilities. Additionally, DESs can act as porogens within SPME sorbents, increasing sorption capacity and, consequently, extraction efficiency. They can also serve as green desorption solvents, replacing traditional volatile organic solvents during the recovery of analytes from sorbent materials. This review synthesizes current knowledge on the implementation of DESs in SPME techniques, critically evaluating their primary advantages and inherent limitations. The novelty of this review lies in the assessment of DES-based SPME through the metrics of greenness and sustainable chemistry. Furthermore, the review identifies research perspectives and priorities to advance DES-based SPME, including: the integration of predictive modeling (COSMO-RS, machine learning) to elucidate DES-analytes interactions; the adoption of 3D printing for the precision fabrication of DES-based sorbents; the standardization of DES-based SPME performance; and the exploration of natural DESs for in vivo SPME in biomedical applications.