Application of Stir Bar Sorptive Extraction (SBSE) Coupled to Thermal Desorption GC-MS for Determination of Ultra-Trace Level Compounds in Aqueous Samples

Importance of the Topic

The ability to detect ultra-trace levels of hydrophobic contaminants in water is critical for ensuring drinking water safety and protecting aquatic ecosystems. Solvent-free, miniaturized extraction approaches offer environmental and operational advantages over traditional liquid–liquid extraction.

Study Objectives and Overview

This work evaluates stir bar sorptive extraction (SBSE) coupled to thermal desorption GC–MS for quantifying sub-ng/L to ng/L concentrations of off-flavor compounds in drinking water and alkylphenols with bisphenol A in river water.

Methodology and Instrumentation

SBSE employed 24 µL PDMS‐coated stir bars stirred at 1 000 rpm and 25 °C for 60–120 min in 10–40 mL aqueous samples. After extraction, bars were rinsed, dried, and thermally desorbed using a GERSTEL TDS‐2/A with CIS‐4 inlet. An Agilent 6890 GC fitted with an HP-5MS column (30 m × 0.25 mm × 0.25 µm) coupled to a 5973N MSD operating in SIM mode provided analyte separation and detection.

Main Results and Discussion

Off-flavor compounds 2-methylisoborneol, geosmin and 2,4,6-trichloroanisole were quantified in 40 mL water with linear calibration (0.2–100 ng/L, r²>0.9987), recoveries of 93–104 % and RSDs of 0.8–2.8 %. Limits of detection ranged from 0.052 to 0.15 ng/L. In situ acetylation of phenolic compounds using K2CO3 and acetic anhydride improved hydrophobicity, enabling determination of alkylphenols and bisphenol A in 10 mL river water at 0.11–3.6 ng/L LODs, recoveries of 85–106 % and RSDs below 11 %.

Benefits and Practical Applications

• Solventless extraction minimizes chemical usage and waste.
• High enrichment factors allow reliable quantification at ultra-trace levels.
• Adaptable to various aqueous matrices including drinking and environmental waters.

Future Trends and Potential Applications

• Design of novel polymer coatings to extend analyte coverage.
• Coupling with high-resolution mass spectrometry for greater selectivity.
• Automated sampling systems for field deployment and real-time monitoring.
• Application to other matrices such as food and biological fluids.

Conclusion

SBSE–TD-GC–MS proves to be a robust, sensitive and eco-friendly approach for ultra-trace analysis of hydrophobic contaminants in water, offering excellent detection limits, linearity, recovery and precision.

Instrumentation

• Twister™ SBSE stir bars (24 µL PDMS)
• GERSTEL TDS-2/A thermal desorption system with CIS-4 inlet
• Agilent 6890 GC with HP-5MS column (30 m × 0.25 mm × 0.25 µm)
• Agilent 5973N MS operated in selected ion monitoring mode

Reference

Baltussen E., Sandra P., David F., Cramers C., Journal of Microcolumn Separations 11, 737–747 (1999)