Use of SBSE for clean-up of QuEChERS extracts from complex matrices

Significance of the Topic

QuEChERS is a popular multi-residue extraction technique valued for its simplicity and cost-effectiveness, but complex sample matrices often introduce interferences that challenge detection limits for trace analytes such as polycyclic aromatic hydrocarbons (PAHs). Integrating stir bar sorptive extraction (SBSE) as a cleanup and enrichment step addresses these limitations by selectively extracting target compounds and reducing matrix effects.

Objectives and Study Overview

This study evaluates the use of SBSE to clean up and concentrate PAHs from QuEChERS extracts of complex matrices. QuEChERS extracts, prepared on behalf of EA Leeds, were subjected to SBSE to assess its effectiveness in improving sensitivity, selectivity, and detection limits when combined with GC-MS/MS analysis.

Methodology

Sample Preparation and SBSE Cleanup:

• Aliquot 1 mL of QuEChERS extract in acetonitrile.
• Add 4 mL of 0.1 M sodium hydrogen carbonate solution.
• Perform SBSE for 90 minutes at 1200 rpm using a 10 mm × 0.5 mm PDMS-coated Twister™ stir bar.
• Rinse Twister with water, dry, and transfer into a thermal desorption (TDU) tube.

Thermal Desorption and GC-MS/MS Conditions:

• Desorb analytes in a GERSTEL Thermal Desorption Unit (TDU) from 40 °C to 300 °C (5 min hold) under splitless conditions.
• Trap analytes on a GERSTEL Cooled Injection System (CIS) at −120 °C, then heat to 300 °C (3 min hold) for injection onto the GC column.
• Analyze using an Agilent 7890B GC coupled to a 7000 Triple Quadrupole MS in multiple reaction monitoring (MRM) mode, with two transitions per analyte.

Instrumentation

• GERSTEL MultiPurpose Sampler (MPS) 2 XL Dual Head
• GERSTEL Cooled Injection System (CIS) 4
• GERSTEL Thermal Desorption Unit (TDU)
• Agilent 7890B Gas Chromatograph
• Agilent 7000 Triple Quadrupole Mass Spectrometer

Main Results and Discussion

Calibration and Recovery:
Calibration curves for PAHs over 25–500 µg/L exhibited excellent linearity (R2 ≥ 0.9992), using quadratic or linear fits as appropriate. Recovery of an analytical quality control sample at 250 µg/L ranged from 78.4 % to 112.6 %, demonstrating robust accuracy across 20 PAH compounds.

Repeatability and Sensitivity:
Duplicate quality control injections showed high method precision. A low-level standard at 2.5 µg/L indicated a signal-to-noise performance corresponding to an estimated limit of detection of approximately 96 ng/L in the cleaned extract.

These findings confirm that SBSE effectively removes polar and high-molecular-weight matrix components while concentrating PAHs, allowing for high-throughput, selective MRM analysis with low detection limits.

Benefits and Practical Applications of the Method

• Combined cleanup and enrichment step reduces overall sample preparation time compared to multi-step SPE procedures.
• Enhanced selectivity and sensitivity for trace PAH analysis in complex food and environmental matrices.
• Compatibility with existing QuEChERS workflows increases laboratory efficiency without additional solvent usage.

Future Trends and Potential Applications

Further method optimization could leverage more sensitive triple quadrupole platforms (e.g., Agilent 7010) to achieve lower detection limits. SBSE may be extended to other semi-volatile or non-polar analyte classes, and automation of Twister desorption can support high-throughput screening in food safety, environmental monitoring, and industrial quality control.

Conclusion

This technical note demonstrates that integrating SBSE as a cleanup and enrichment step for QuEChERS extracts significantly improves the analysis of PAHs in complex matrices. The approach delivers accurate recoveries, excellent precision, and low detection limits using targeted MRM on a triple quadrupole GC-MS, offering a streamlined and robust solution for trace-level monitoring.

Reference

• GERSTEL Application Note 6/2010a: Alternative Procedure for Extraction and Analysis of PAHs in Seafood by QuEChERS-SBSE-GC-MS.
• GERSTEL Application Note 6/2010b: High Throughput Method for the Determination of PAHs in Seafood by QuEChERS-SBSE-GC-MS.
• Anatune Technical Note AS127: Trace Analysis of Polycyclic Aromatic Hydrocarbons (PAHs) in Water Using Twister SBSE Technology.