Sample Cleanup: Method Development for Solid Phase Extraction and Beyond

Significance of the Topic

Solid-phase extraction (SPE) remains a cornerstone of modern analytical workflows, offering robust sample cleanup and pre-concentration for a broad spectrum of applications in environmental, food, pharmaceutical, and clinical analysis. By selectively removing interferences while retaining target analytes, SPE enhances method sensitivity, reproducibility, and throughput, supporting regulatory compliance and high-throughput screening.

Objectives and Overview of the Study

This presentation outlines a structured approach to SPE method development and troubleshooting, with a survey of current and emerging sample cleanup technologies. Key objectives include:

• Defining criteria for SPE selection based on analyte chemistry and matrix properties.
• Describing workflow steps—conditioning, loading, washing, elution—and their optimization.
• Illustrating example methods for water and food analysis.
• Introducing recent SPE and pass-through cleanup products for lipids, PFAS, and mycotoxins.

Methodology and Instrumentation

Method development follows a systematic SPE workflow:

• Sample Pretreatment: pH adjustment and dilution to optimize analyte form and matrix compatibility.
• Sorbent Conditioning and Equilibration: wetting with organic solvent followed by aqueous buffer.
• Sample Loading: controlled flow (vacuum or positive pressure) to maximize retention.
• Washing: removal of non-target compounds using weak solvents or buffers, typically ≥2× void volume.
• Elution: recovery of analytes with strong organic solvents, applied in aliquots or soaking steps.

Instrument platforms and consumables include:

• Agilent SPE cartridges (open-top, Luer-top, 96-well plates, pipette tips) and sorbent chemistries (C18, C8, silica, polymeric, mixed-mode, ion exchange).
• Processing systems: VacElut and PPM vacuum/positive-pressure manifolds, VersaPlate racks.
• Detection: LC/MS/MS, GC/MS, HPLC-FL/UV and LC-Q-TOF for method validation and performance benchmarking.

Main Results and Discussion

• SPE Sorbent Selection: Nonpolar phases (C18, C8, phenyl, polymeric) excel for hydrophobic analytes in polar matrices; mixed-mode and ion-exchange phases broaden applicability to ionic compounds.
• Troubleshooting Strategies: Low recovery is addressed by pH adjustments, flow-rate reduction, solvent strength tuning, and sorbent conditioning. Dirty extracts can be improved by multistep washes, selective sorbents, or mixed-mode stacks.
• Example Methods:

• Bond Elut PPL for 39 pharmaceuticals and personal care products (PPCPs) in drinking water: dual-step elution with acidified methanol/acetonitrile.
• Bond Elut Plexa for simultaneous extraction of PAHs, chlorinated pesticides, and triazines from 800 mL water using sequential ethyl acetate and dichloromethane fractions.

• New Cleanup Products:

• EMR-Lipid SPE for lipid removal in metabolomic studies, enabling smaller sample volumes and improved reproducibility over liquid–liquid extraction.
• PFAS WAX SPE cartridges tailored for regulated PFAS methods (EPA-533, EPA-1633, ISO 21675) with ultraclean sorbent and blank performance.
• Bond Elut HLB polymers featuring hydrophilic–lipophilic balance, high capacity, wide pH tolerance, and broad analyte recovery.
• Carbon S hybrid sorbent for pigment removal in food and environmental matrices, available in QuEChERS, SPE cartridges, and pass-through filtration formats.
• Captiva EMR series for PFAS in food, mycotoxins, and mixed-mode pesticide cleanup, offering targeted pass-through cleanup with minimal manual steps.

Benefits and Practical Applications

SPE and targeted pass-through solutions deliver:

• Enhanced method sensitivity and lower detection limits through effective cleanup and concentration.
• Improved reproducibility and reduced matrix effects, critical for LC/MS and GC/MS quantitation.
• Streamlined workflows with reduced solvent usage, faster processing times, and compatibility with automated platforms.
• Compliance with regulatory protocols (e.g., EPA, ISO) across water, food, and biological testing.

Future Trends and Opportunities

Emerging directions in sample cleanup include:

• Integration of mixed-mode sorbents for one-step removal of diverse interferences (lipids, proteins, pigments, salts).
• Miniaturized and high-throughput formats (96-well, pipette tips) with robotics and online SPE coupling.
• Advanced hybrid materials (carbon nanostructures, molecularly imprinted polymers) for ultra-selective cleanup.
• Expansion of pass-through modalities for challenging analyte classes such as PFAS, mycotoxins, and lipidomics.

Conclusion

A methodical approach to SPE selection, combined with rigorous troubleshooting and adoption of new cleanup chemistries, enables robust sample preparation across diverse analytical challenges. By leveraging tailored sorbents and formats, laboratories can achieve higher throughput, better data quality, and regulatory compliance in environmental, food, and life-science applications.