Off-line supercritical fluid extraction/gas chromatography-mass spectrometry analysis of pesticides in fish

Off-line Supercritical Fluid Extraction/Gas Chromatography-Mass Spectrometry Analysis of Pesticides in Fish

Importance of the Topic

Monitoring pesticide residues in fish tissue is critical for protecting public health and informing consumption advisories issued by regulatory agencies. Conventional extraction methods, such as accelerated solvent extraction (ASE), often involve large solvent volumes and may co-extract matrix components that interfere with analysis. Employing supercritical fluid extraction (SFE) offers a cleaner, more efficient alternative that can reduce solvent consumption and matrix effects while maintaining sensitive detection limits.

Study Objectives and Overview

This study evaluates an off-line SFE protocol combined with gas chromatography–tandem mass spectrometry (GC-MS/MS) for quantitative analysis of 18 widely used organochlorine pesticides in fish muscle. Using walleye samples with low lipid content (%L=0.9), the work aims to optimize SFE parameters, assess recovery rates, minimize matrix interference, and demonstrate suitability for routine monitoring workflows.

Methodology and Instrumentation

Samples of frozen walleye fillets were homogenized and freeze-dried. Aliquots (0.5 g) were spiked with internal standards, overlaid with activated alumina to serve as an in-vessel cleanup sorbent, then subjected to SFE under the following conditions:

• Vessel temperature: 50 °C
• Pressure: 30 MPa with 100 % CO₂ at 1.0 mL/min
• Static extraction: 25 min; dynamic extraction: 30 min
• Trap column: Shimadzu C18 (4.6 × 50 mm, 5 µm), 20 °C during extraction, 50 °C for elution with hexane rinse

Used Instrumentation

• Supercritical fluid extractor (Shimadzu SFE system)
• GC-MS/MS: GCMS-TQ8040 with AOC-20i/s autosampler
• Capillary column: SH-Rxi-5MS (30 m × 0.25 mm, df = 0.25 µm)
• Injection: 275 °C splitless, 1 µL; linear velocity control at 43.5 cm/s
• MS settings: ion source 230 °C, interface 290 °C; event time 0.3 s
• Oven program: 50 °C (0.5 min), 28 °C/min to 265 °C, 3 °C/min to 285 °C, 25 °C/min to 330 °C (1 min)

Main Results and Discussion

Calibration for 18 pesticides showed linearity over 10–100 ppb with R² > 0.98. Initial recoveries from low-lipid walleye ranged widely (40–105 %), with poorer performance for compounds such as 4,4′-DDT and methoxychlor. Lowering the trap column temperature during extraction improved retention and desorption profiles. Spiking experiments demonstrated that adding a small amount of corn oil to low-lipid samples prior to SFE substantially enhanced recoveries to 77–98 % for nearly all analytes.

Benefits and Practical Applications

• Reduced solvent use and lower matrix interferences compared to traditional extraction methods
• A single-step extraction and cleanup simplifies sample preparation
• High-throughput capability—automated processing of up to 48 samples
• Sensitivity and accuracy suitable for regulatory monitoring and environmental surveys

Future Trends and Opportunities

Advances in SFE hardware and expanded sorbent chemistries promise even greater selectivity and throughput. Integration with other high-resolution detectors (e.g., orbitrap MS) could further improve trace-level quantification. The approach may be extended to other low-fat matrices or complex environmental samples by tailoring co-matrix additives and cleanup strategies.

Conclusion

Off-line SFE coupled with GC-MS/MS provides a robust, efficient workflow for quantifying organochlorine pesticides in fish tissue. Optimized extraction parameters, in-vessel cleanup, and strategic use of co-matrix oils yield consistent recoveries and minimal interference, supporting reliable routine analysis.

Reference

No formal reference list provided in the source document.