The Complete Guide to Solid Phase Extraction (SPE)

Importance of the Topic

Solid phase extraction (SPE) is a cornerstone of modern analytical chemistry for isolating target analytes from complex matrices. By selectively retaining compounds of interest and removing interfering substances, SPE improves detection sensitivity, extends column life, concentrates samples for enhanced chromatographic performance, and enables solvent compatibility for both gas and liquid chromatography.

Objectives and Overview

This guide presents a systematic workflow for SPE method development and application, focusing on polymer-based (Strata-X) and silica-based (Strata) sorbents. It covers:

• Sorbent selection based on retention mechanisms (reversed phase, ion exchange, normal phase, mixed-mode)
• Sample pre-treatment protocols for biological, environmental, and food matrices
• General starting methods including conditioning, loading, washing, and elution guidelines
• Industry application examples across pharmaceuticals, clinical research, food safety, and environmental testing

Methodology and Instrumentation

Methodology

• Step 1: Choose sorbent chemistry and particle/pore size tailored to analyte polarity, ionic state, and sample volume
• Step 2: Pre-treat samples to achieve uniform liquid phase, control pH, reduce viscosity, and remove particulates (e.g., protein precipitation, homogenization, filtration)
• Step 3: Apply starting SPE protocols: condition cartridge (organic solvent then water or buffer), load sample, perform sequential washes to eliminate matrix contaminants, and elute analytes in minimal volume based on bed volume guidelines (4–8 bed volumes)
• Optimization: Adjust wash/elution solvents, pH, and solvent composition through small-scale elution studies

Instrumentation

• LC/MS/MS platforms (e.g., SCIEX Triple Quad 4500, API 4000) with electrospray ionization for pharmaceutical and clinical assays
• GC/ECD and GC/MS with Zebron ZB-MultiResidue columns for pesticide and environmental analyses
• Core-shell UHPLC columns (e.g., Kinetex C18, Biphenyl, XB-C18) for rapid separations
• Vacuum and positive pressure SPE manifolds for 1 mL, 3 mL, 6 mL tubes and 96-well plates

Main Results and Discussion

• Microelution SPE using Strata-X 2 mg plates enabled skipping the dry-down step, preserving thermolabile peptides (e.g., DALDA C8) with 95% recovery and 5.7% CV, compared to ~50% recovery when evaporated.
• Comparison of SPE and liquid-liquid extraction (LLE) for diclofenac in plasma: SPE delivered 86% absolute recovery (10% RSD) versus 46% (35% RSD) by LLE.
• Amphetamines in urine were quantified at levels 25% below SAMHSA cut-offs using Strata-X-C microelution plates, with recoveries of 82–108% and RSDs under 16%.
• Extraction of cortisol, cortisone, prednisone, and prednisolone from urine achieved >80% recovery across low and high QC levels using Strata-X polymeric SPE with optimized elution solvent.
• Strata Alumina-N SPE efficiently removed humic acids and isolated 16 chlorinated pesticide residues from poultry fat, meeting EPA 550.1 criteria by GC/ECD.
• Strata-X-A SPE of phenylbutazone in ground meat yielded >90% recovery and high precision in a 5-minute LC/MS/MS run on a Kinetex core-shell column.
• Strata PAH sorbent provided consistent high recoveries for 16 PAHs in water samples and effectively eliminated humic interference.

Benefits and Practical Applications

• High sample throughput with 96-well microelution and automated manifolds
• Reduced solvent consumption and minimal elution volumes for faster downstream analysis
• Robust pH stability (1–14) and broad loading capacity for diverse matrices
• Enhanced reproducibility and method ruggedness via well-characterized sorbent chemistries
• Versatile applications across pharmaceutical development, clinical assays, food safety, and environmental monitoring

Future Trends and Potential Uses

Advancements in SPE design are expected to include micro- and nano-sorbent formats, integration with online and in-line automation, coupling to mass spectrometry for direct analysis, and expansion into supercritical fluid SPE. Emerging sorbent chemistries tailored for metabolomics, proteomics, and trace-level environmental contaminants will further broaden SPE utility.

Conclusion

SPE remains an essential and adaptable sample preparation approach. The combination of polymeric and silica-based sorbents, guided by systematic method development, delivers ultra-clean extracts, high recoveries, and reproducible performance across a wide range of analytical challenges.