Low Background Solid Phase Extraction and Capillary GC Analysis of Chlorinated Pesticides

Importance of the Topic

• Chlorinated pesticides are persistent environmental contaminants of concern at trace levels in water.
• Rapid, reliable sample preparation methods are essential for on-site screening and decision making at hazardous waste sites.
• Solid phase extraction (SPE) with low-background, high-capacity sorbents enables efficient enrichment of semivolatiles prior to GC analysis.

Objectives and Study Overview

• Develop and evaluate a polymerically bonded octylsilane-silica SPE packing (ENVI-8) for extraction of 21 chlorinated pesticides from aqueous hazardous waste samples.
• Demonstrate performance at two concentration levels: a high “capacity” level (250 ng each pesticide/100 mL) and a low “contamination” level (10 ng/100 mL).
• Establish a rapid, low-background SPE protocol compatible with GC-ECD screening methods (US EPA quick-turnaround style).

Methodology

• Condition SPE tubes (0.5 g ENVI-8 in 6 mL glass, Teflon frits) with methanol and aqueous buffer.
• Spike 100 mL water samples (pH 5–7) with pesticide standards and surrogate decachlorobiphenyl.
• Load samples at 5 mL/min under vacuum (Visiprep DL manifold).
• Dry sorbent under nitrogen for 2–3 minutes (Visidry attachment).
• Elute analytes with two 5 mL portions of hexane:acetone (90:10), reduce to 1 mL under nitrogen.

Instrumentation

• GC with electron capture detector (ECD).
• 0.53 mm × 15 m PTE-5 QTM capillary column, 0.5 μm film.
• Visiprep DL SPE Vacuum Manifold (12- or 24-port) and Visidry Drying Attachment.
• Visiprep large volume sampler with custom glass adapters.

Main Results and Discussion

• High Recovery: At the 250 ng level, average recoveries exceeded 91% for most pesticides, with coefficient of variation (CV) < 10% for most compounds.
• Low-Level Performance: At 10 ng/100 mL, recoveries remained high (77–104%) and background interferences were minimal.
• Consistency: Lot-to-lot SPE variability was acceptable; endrin and its ketone showed greater variation but still within screening tolerance.
• Low Background: Unused tubes yielded negligible pesticide contamination, ensuring reliability at trace levels.

Benefits and Practical Applications

• Rapid Screening: SPE procedure completes sample prep in under 30 minutes, facilitating on-site decisions.
• High Sensitivity: Compatible with GC-ECD detection limits (10–250 ng/100 mL).
• Durability: Polymeric bonding resists pH extremes and enhances sorbent capacity.
• Flexibility: Method applicable to a wide range of chlorinated semivolatiles in environmental monitoring and QA/QC.

Future Trends and Applications

• Integration with automated SPE-GC platforms for higher throughput.
• Extension to emerging contaminants (e.g., brominated flame retardants, polar pesticides) using tailored sorbent chemistries.
• Combination with mass spectrometric detection for non-target screening and confirmatory analysis.
• Miniaturized SPE cartridges and field-deployable devices for remote sampling.

Conclusion

• The ENVI-8 SPE packing delivers robust, low-background extraction of chlorinated pesticides from aqueous matrices.
• High recovery and reproducibility at both high and trace levels support its use in rapid screening applications.
• The described workflow offers a practical, sensitive solution for environmental monitoring and hazardous site assessments.

References

• Sigma-Aldrich Supelco Application Note 64, 2004.
• US EPA Office of Solid Waste Quick-Turnaround Screening Methods.