Theoretical and Practical Comparison of Solid Phase Micro-extraction and Liquid-Liquid Extraction with Large Volume Injection for Analysis of Aqueous Samples by Gas Chromatography

Significance of the Topic

Solid-phase microextraction (SPME) and combined liquid-liquid extraction with large volume injection (LVI) have become essential for ultra-trace analysis of organic contaminants in water at sub-part per billion concentrations. By enabling efficient preconcentration and minimizing solvent use, these methods support environmental monitoring, industrial quality control and food safety screening.

Objectives and Study Overview

This study compares theoretical recovery and practical performance of SPME versus micro-liquid-liquid extraction with large volume injection (MLLE-LVI) for gas chromatographic analysis of aqueous samples. Through partition theory calculations and experimental evaluation using a polycyclic aromatic hydrocarbon (PAH) test mixture, it assesses extraction efficiency, detection limits, linear range and operational factors.

Methodology

Theoretical recoveries were derived from fundamental partition equations relating phase volumes and partition coefficients. Experimentally, an EPA Method 610 PAH mixture was diluted in water, extracted by SPME fibers or 1 mL liquid-liquid extraction, and analyzed by capillary gas chromatography. Recoveries were predicted over partition coefficient values spanning four orders of magnitude and compared with observed chromatographic responses.

Instrumentation Used

• Agilent 5890 Series II gas chromatograph with flame ionization detector
• Atas Optic 2 large volume injection inlet with Tenax-packed liner
• Supelco SPB-1 capillary column (30 m × 0.32 mm × 0.25 µm)
• Hamilton gas-tight syringe for sample introduction

Main Results and Discussion

Theoretical analysis indicates MLLE achieves near-exhaustive extraction down to partition coefficients of ~20, whereas SPME requires coefficients above 10⁴ for exhaustive transfer. However, injection volume limits for MLLE-LVI (100 µL) contrast with near-complete desorption of SPME fibers. Consequently, SPME delivers higher on-column mass for analytes with partition coefficients >200, while MLLE-LVI is superior for K <200. Experimental chromatograms confirm volatility discrimination in LVI and more uniform transfer in SPME.

Benefits and Practical Applications of the Method

• SPME eliminates solvent consumption and offers efficient preconcentration for high-partition-coefficient analytes
• MLLE-LVI supports compounds with moderate partitioning by injecting larger extract volumes
• Both approaches facilitate automation and simplified workflows in environmental, industrial and food laboratories

Future Trends and Potential Applications

Advances in novel fiber coatings, automated sampling and improved inlet designs are expected to lower detection limits further. Integration of SPME with tandem mass spectrometry and adaptation of MLLE-LVI to polar or complex matrices will expand application areas. Emerging sorbent materials and on-line extraction systems will enhance throughput and selectivity.

Conclusion

A combined theoretical and practical comparison demonstrates that analyte partition coefficient dictates the optimal extraction approach: SPME is preferred for strongly lipophilic compounds (K >200), whereas MLLE-LVI excels for moderately partitioning analytes. Analysts should consider solvent consumption, detection requirements and matrix effects when selecting between these techniques.

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