Review of Packed Sorbent Solid-Phase Extraction and Microextraction Methods From Manual to Automated

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Studies published over the last five years have focused on fully or semi-automated approaches and their applications in extraction of both organic and inorganic pollutants, while modern robotic tools and 3D printing are starting to make impacts.

Four researchers in Iran have collaborated on a new report that reviews advanced studies published from 2018 to 2022 of sorbent-packed methods of solid-phase extraction (SPE), micro-solid-phase extraction (µSPE), and solid-phase microextraction (SPME), and their various associated techniques (1). Automated approaches which demonstrate advantages such as high sample throughput, sensitivity, extraction efficiency and reproducibility are assessed in the paper, but the research team also took care to highlight semi-automated or manual methods, as well as the history of SPE that has led to the current menu of options.

Solid-phase extraction (SPE) is a sample preparation technique widely used in analytical chemistry. It involves the separation and purification of compounds from complex mixtures using a solid adsorbent material. In SPE, a sample is passed through a column or cartridge containing the adsorbent, where specific compounds of interest selectively interact with the adsorbent while unwanted substances are washed away. After the sample is loaded onto the column, the adsorbed compounds are eluted using a solvent, resulting in a concentrated and purified analyte fraction. SPE is employed to enhance sensitivity, remove interfering substances, and prepare samples for subsequent analysis.

The review article, published in the Journal of Chromatography A and co-authored by Mahsa Samadifar, Yadollah Yamini, and Mohammad Mahdi Khataei of Tarbiat Modares University in Tehran and Mahboue Shirani of the University of Jiroft, additionally investigates the relatively recent integration of technologies such as robotic platforms and 3D printing, noting that human error in manual extraction methods is a cause for decreased repeatability, while high back pressure and potential for column clogging are problems inherent in semi-automation (1).

Solid-phase extraction (SPE) by packed sorbent, which is described by the authors as a cylinder packed with an adsorbent in which granular activated carbon was originally the sorbent, gained popularity in the 1950s (1). But a wide range of sorbents can be used in SPE, and many novel sorbents have been introduced in that intervening time, which the researchers said has helped improve simplification, miniaturization, and automation of SPE.

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To be sure, as this review also covers, SPE itself has splintered into specific miniaturized or automated techniques including solid-phase microextraction (SPME), in-tube, needle hub, and pipette tip SPE, dispersive and magnetic dispersive µSPE, stir-bar sorptive extraction (SBSE), and microextraction in a packed syringe (MEPS) (1). Many of these offshoots, the researchers said, are more compatible with packed sorbent, namely adding lab-on-a-chip (LOC) and lab-on-valve (LOV) to that list.

These methods have gradually been developed, in part, in the interest of separating and determining organic and inorganic pollutants, with SPE-based operations combined either with high performance liquid chromatography coupled to ultraviolet-visible (UV-vis), fluorescence (FL), diode array detector (DAD), or mass spectrometry (MS) detectors, or gas chromatography (GC) coupled to tandem mass spectrometry (MS/MS) or flame ionization detection (FID) for the analysis of organic pollutants, according to the researchers (1).

Summarizing their review of SPE approaches compatible with packed sorbent, the researchers said these methods are more compatible with automation, which naturally leads to higher precision and accuracy (1). Such techniques also tend to be easier and faster. But one final consideration is their greenness. In keeping with the terms of green analytical chemistry (GAC), the automation facilitated by SPE with packed sorbent promises a more environmentally friendly setting for separations, even when compared to custom or miniature forms of extraction.

Reference

(1) Samadifar, M.; Yamini, Y.; Khataei, M. M.; Shirani, M. Automated and semi-automated packed sorbent solid phase (micro) extraction methods for extraction of organic and inorganic pollutants. J. Chromatogr. A 2023, 1706, 464227. DOI: 10.1016/j.chroma.2023.464227