Solid Phase Microextraction Theory and Basics of a modern Sample Preparation Technique

Importance of the Topic

Solid phase microextraction (SPME) has transformed sample preparation by integrating extraction and concentration into a single, solvent-free step. Its micro-scale fiber technology offers high sensitivity and rapid turnaround for trace analysis across diverse matrices, including water, air, soil, food, forensic and clinical specimens. The ability to automate SPME on autosamplers further enhances its appeal for high-throughput laboratories.

Objectives and Study Overview

This bulletin presents the fundamental theory and operational principles of SPME, traceable to its invention by Prof. Janusz Pawliszyn at the University of Waterloo. Key aims include:

• Describing fiber assemblies and coating chemistries
• Explaining adsorption/desorption mechanisms and equilibrium modeling
• Comparing extraction modes (headspace vs direct immersion)
• Reviewing factors affecting recovery (temperature, stirring, sample modifications)
• Illustrating practical applications through representative case studies

Methodology and Instrumentation

SPME relies on fused-silica or Stableflex fibers coated with absorbent films (e.g. PDMS, PA, PEG) or adsorbent particles (CAR-PDMS, PDMS-DVB, CW-DVB). Extraction proceeds by exposing the fiber to sample headspace or direct immersion until an equilibrium of analyte partitioning is reached. Thermal desorption in a gas chromatograph inlet releases analytes to analytical columns. Key instrumentation includes:

• Manual and autosampler SPME holders (Varian AS-8200, CTC CombiPal)
• Gas chromatographs equipped with split/splitless inlets and various column types (SPB-35, Supel-Q PLOT, MDN-5)
• Detectors such as mass spectrometry (quadrupole), electron capture (ECD) and flame ionization
• Controlled heating, stirring, salt addition and pH adjustment systems

Main Results and Discussion

Comparative studies demonstrate that:

• Carboxen/PDMS fibers excel at extracting light volatiles (C2–C6 hydrocarbons, sulfur gases, nitrosamines) from air or headspace
• PDMS of different film thicknesses optimizes nonpolar analyte uptake, while polar polymers (PA, PEG) target phenols and alcohols
• Dual-coated fibers (DVB/Carboxen/PDMS) extend molecular weight range and enhance capacity for aroma compounds (MIB, geosmin) at ppt levels
• Extraction efficiency benefits from sample salting out, acidification for phenols, and elevated temperatures for headspace analyses
• Liner internal diameter influences desorption kinetics and peak shape for gaseous VOCs

Equilibrium models quantify analyte mass on fiber (ns = KVfC0Vs/(KVf+Vs)) and guide optimization of extraction time to reach equilibrium for different compounds.

Benefits and Practical Applications

SPME offers numerous advantages:

• One-step, solvent-free sample preparation
• Trace-level sensitivity and quantitative performance
• Compatibility with liquids, gases and solids
• Automatable workflows for high-throughput laboratories
• Wide application scope including environmental monitoring, flavor and fragrance analysis, forensic drug screening, and QA/QC in pharmaceutical and chemical industries

Future Trends and Potential Applications

Ongoing developments are expected to include:

• Novel fiber materials (metal cores, advanced polymer composites) with tailored porosity
• On-fiber derivatization reagents for reactive analytes
• Integration with liquid chromatography and ambient ionization mass spectrometry
• Miniaturized, field-deployable SPME devices for real-time monitoring
• Biocompatible fibers for in vivo sampling in biological studies

Conclusion

SPME is a versatile, robust sample preparation technique that streamlines trace analysis while eliminating solvents. Its adaptability to multiple matrices, combined with high sensitivity and automation potential, ensures continued growth in analytical laboratories worldwide.