Cleanup of Hazardous Waste Site Samples by Solid Phase Extraction

Significance of the Topic

Effective cleanup and analysis of pesticide residues in samples from hazardous waste sites is critical to ensure compliance with environmental regulations and to protect human health. Solid phase extraction (SPE) using Florisil sorbents offers a reliable approach to remove matrix interferences and concentrate target analytes prior to chromatographic analysis. This method facilitates accurate quantification of persistent organic pollutants in water, soil, and sediment matrices.

Objectives and Overview

This study evaluates the performance of ENVI-Florisil SPE tubes in the US EPA Contract Laboratory Program (CLP) pesticide method. The primary goal is to confirm that these commercially available tubes deliver recoveries between 80 and 120 percent for the nine priority pesticides specified by the CLP protocol. Both 0.5 g and 1.0 g sorbent bed configurations were assessed at mid-level analyte concentrations.

Methodology and Instrumentation

The SPE procedure follows the EPA CLP guidelines with minor adaptations:

• Conditioning: Tubes were preconditioned with 5 mL of 90:10 hexane:acetone.
• Sample Loading: A 0.5 mL aliquot of pesticide standard mix was applied to each tube.
• Elution: Analytes were eluted using 9.0 mL of hexane:acetone at a dropwise rate, followed by 2.0 mL of pure hexane.
• Concentration: The combined eluants were reduced to a final volume of 1.0 mL for manual injection.

Gas chromatographic analysis was performed on a 30 m × 0.53 mm ID, 1.0 µm film SPB-608 fused silica capillary column. Detector and oven temperature programs adhered to the CLP pesticide method specifications.

Used Instrumentation

• ENVI-Florisil SPE tubes (0.5 g and 1.0 g Florisil packing, 6 mL polypropylene tubes with stainless steel frits)
• SPB-608 fused silica capillary GC column (30 m × 0.53 mm ID, 1.0 µm film)
• Standard pesticide mix containing alpha- and gamma-BHC, heptachlor, endosulfan I, dieldrin, endrin, 4,4'-DDD, 4,4'-DDT, and methoxychlor in hexane

Results and Discussion

Recovery experiments were conducted at mid-level concentrations for both bed sizes. Mean recoveries exceeded 82% for all nine pesticides, with values spanning from approximately 89% to 110%. Key findings include:

• Alpha- and gamma-BHC recoveries of around 90% for both 0.5 g and 1.0 g beds.
• Dieldrin and 4,4'-DDT recoveries near 95%.
• Endrin showed slightly higher recovery on 1.0 g beds (108%) compared to 0.5 g (93%).
• Methoxychlor recovery averaged above 91% in both configurations.

These results confirm that ENVI-Florisil tubes meet the EPA CLP requirement of 80–120% recovery, while offering consistent performance across multiple production lots.

Benefits and Practical Applications

The use of ENVI-Florisil SPE tubes provides:

• Reduced matrix interferences through selective sorbent cleanup.
• High and reproducible analyte recoveries in complex environmental samples.
• Flexible bed sizing (0.5 g or 1.0 g) to accommodate different extract volume requirements.
• Compatibility with manual or automated GC injection systems.

This approach supports routine monitoring of pesticide residues in water, sediment, and soil under regulatory frameworks.

Future Trends and Potential Applications

Emerging directions include:

• Integration of SPE with high-resolution mass spectrometry for enhanced sensitivity and selectivity.
• Development of mixed-mode sorbents to target a broader range of polar and non-polar analytes in a single cleanup step.
• Miniaturization and automation of SPE workflows to reduce solvent consumption and increase throughput.
• Application of SPE methods to novel environmental contaminants such as neonicotinoids and per- and polyfluoroalkyl substances (PFAS).

Conclusion

ENVI-Florisil solid phase extraction tubes have been demonstrated to fulfill the stringent recovery criteria of the EPA CLP pesticide method. The method offers robust cleanup, high analyte recoveries, and adaptability to different sample types and instrumentation. This makes it a valuable tool for environmental laboratories engaged in pesticide monitoring at hazardous waste sites.

Reference

1. US EPA Contract Laboratory Program Statement of Work for Organic Analysis, Multimedia Multiconcentration, Doc. No. 0LM01.0