Solid Phase Microextraction of Alcohols and Small Polar Analytes for Capillary GC

Importance of the Topic

Solid Phase Microextraction (SPME) represents a rapid, solvent-free approach to isolating volatile and semi-volatile compounds directly from aqueous and biological samples. By eliminating liquid solvents and minimizing sample handling, SPME accelerates analytical workflows, reduces environmental impact, and enhances sensitivity for trace polar analytes such as alcohols and small organics.

Objectives and Study Overview

This study evaluates a novel 65 µm Carbowax/divinylbenzene fiber for extracting alcohols and other polar analytes from water and blood. Two sampling modes—direct immersion and heated headspace—are compared to establish linearity, detection limits, reproducibility, and compatibility with GC/MS and GC/FID analysis.

Methodology and Instrumentation

Samples were prepared in neutral pH water saturated with 27 % NaCl to enhance volatility. For headspace SPME, vials (4 mL) were equilibrated at 50 °C and exposed for 1.5 minutes. Direct immersion extractions used the same fiber in liquid phase. Analytes were thermally desorbed in a split/splitless injection port at 250 °C and separated on capillary columns followed by detection:

• GC/MS (quadrupole) in selected ion monitoring for quantitation of methanol, ethanol, acetone, acetonitrile, isopropanol, n-propanol, and ethyl acetate
• GC/FID for comparison of baseline noise and sensitivity

Main Results and Discussion

Headspace SPME delivered lower limits of detection (0.05–0.1 ppm) and better precision (%RSD < 6 %) for most alcohols compared to direct immersion (LOD 0.25–0.75 ppm). Linearity extended from sub-ppm to 100 ppm (ethyl acetate 0.01–50 ppm), surpassing US EPA Method 1671 requirements. In forensic blood analyses, ethanol was quantified at 25 mg/dL with r2 = 1.00 and a coefficient of variance of 2.2 % at 100 mg/dL, demonstrating robustness in complex matrices.

Benefits and Practical Applications

SPME with Carbowax/DVB fiber offers:

• Solvent-free, rapid sample preparation
• High sensitivity for trace polar analytes
• Minimal matrix interference in water and biological fluids
• Compatibility with existing GC/MS and GC/FID systems
• Field-deployable sampling for forensic and environmental monitoring

Future Trends and Potential Applications

Development of porous polymer and polar coatings will broaden SPME to semi-volatile analytes such as anilines, benzidines, and glycols at low ppb levels. Integration with automated autosamplers and miniaturized GC detectors will support on-site environmental screening, clinical diagnostics, and food safety testing. Continued coating innovations may enable direct solid sampling and expanded pH-range extractions.

Conclusion

The 65 µm Carbowax/divinylbenzene SPME fiber provides a fast, sensitive, and reproducible method for extracting alcohols and small polar compounds from aqueous and biological samples. Heated headspace mode offers superior detection limits and precision, making this approach valuable for environmental analysis, forensic toxicology, and quality-control laboratories.

Instrumentation Used

• SPME fiber, 65 µm Carbowax/divinylbenzene (Supelco)
• SPME manual holder or autosampler upgrade (Varian 8100/8200)
• Gas chromatograph with split/splitless injector (250 °C)
• GC/MS quadrupole detector (SIM mode)
• GC/FID detector (260 °C)
• Capillary columns: SPB-1 Sulfur (30 m×0.32 mm, 4 µm), Nukol (30 m×0.25 mm, 0.25 µm), SUPELCOWAX 10 (30 m×0.20 mm, 0.20 µm)

Reference

1. Shirey R., Mani V., “New Developments in Solid Phase Microextraction — Polar Analytes and Fast Analysis,” 1995 Pittsburgh Conference, Supelco publication T495014.