Solid Phase Microextraction of Semivolatile Compounds

Importance of the Topic

Solid Phase Microextraction (SPME) represents a significant advancement in environmental and analytical chemistry by enabling solventless extraction of organic pollutants from water. Traditional EPA protocols rely on liquid–liquid extraction with chlorinated solvents, which pose environmental and health hazards and require extensive handling and disposal. SPME addresses these issues by integrating sampling, concentration, and injection into a single step, reducing solvent use, improving safety, and streamlining laboratory workflows.

Objectives and Study Overview

This application note evaluates the performance of a 7 µm polydimethylsiloxane (PDMS) SPME fiber for the extraction of semivolatile organic compounds—including polynuclear aromatic hydrocarbons (PAHs) and phthalate esters—spiked into aqueous samples at concentrations between 10 ppb and 200 ppb. The study aims to demonstrate the linearity, sensitivity, and reproducibility of SPME coupled with GC–MS analysis compared to established methods.

Methodology and Instrumentation

A 7 µm PDMS-coated fused-silica fiber was immersed directly in 4 mL water samples spiked with target analytes. Extraction times ranged from 2 to 30 minutes, reaching equilibrium within 15 minutes under the selected conditions. After sampling, the fiber was thermally desorbed into a GC injection port at 280 °C (split/splitless mode), transferring the analytes to a narrow-bore PTE™-5 capillary column (30 m × 0.25 mm ID × 0.25 µm film) under a helium carrier flow of 40 cm/s at 60 °C. Detection was performed by an MS detector scanning m/z 45–465 at 0.6 s/scan.

Main Results and Discussion

The response factors for PAHs and phthalates exhibited good linearity across the tested concentration range, with relative standard deviations (RSDs) below 13 % for most compounds. Nonpolar analytes such as naphthalene, phenanthrene, and anthracene showed RSDs between 3.5 % and 9.8 %. More polar phthalates (dimethyl- and diethylphthalate) showed higher RSDs (20.7 % and 26.8 %, respectively), reflecting lower affinity for the nonpolar PDMS coating. Overall, the method achieved parts-per-trillion detection limits with ion-trap MS detectors, demonstrating high sensitivity.

Benefits and Practical Applications

SPME offers multiple advantages for water analysis laboratories:

• Elimination of chlorinated solvents, reducing environmental impact and disposal costs.
• Minimized sample preparation time by combining extraction and preconcentration.
• Reusability of fibers, lowering per-sample costs.
• Compatibility with standard GC and GC–MS systems for volatile to semivolatile analytes.
• High sensitivity and reproducibility suitable for trace-level environmental monitoring.

Applied Instrumentation

The study employed:

• SPME fiber and holder (7 µm PDMS coating) for direct aqueous sampling.
• Capillary GC with split/splitless injection port (280 °C).
• PTE™-5 fused-silica column (30 m × 0.25 mm ID × 0.25 µm film).
• Helium carrier gas at 40 cm/s and temperature ramp from 60 °C to 320 °C at 10 °C/min.
• Mass spectrometer scanning m/z 45–465.

Future Trends and Potential Uses

Emerging directions in SPME research include:

• Development of polar fiber coatings (e.g., polyacrylate) for improved recovery of polar semivolatiles.
• Integration with automated sampler interfaces to increase throughput and reproducibility.
• Expansion to complex matrices such as soils, tissues, and food products.
• Coupling with portable GC–MS systems for field-based environmental monitoring.
• Advances in fiber chemistries to target a broader range of analytes, including emerging contaminants.

Conclusion

The 7 µm PDMS SPME fiber proves to be an efficient, reproducible, and environmentally friendly alternative to solvent-based extraction for semivolatile organic compounds in water. The method delivers excellent linearity, low detection limits, and streamlined sample preparation, making it a valuable tool for routine environmental analysis and regulatory compliance.

References

1. Zhang Z., Pawliszyn J. Anal. Chem. 65:1843–1852 (1993).