Automated Solid-Phase Extraction of Phthalates for Drinking Water Samples

Significance of the topic

Phthalates are widespread plasticizers used in consumer goods and packaging. They can leach into water supplies, posing potential health risks even at trace levels. Monitoring phthalate contamination in drinking water is essential to comply with regulatory limits, protect public health, and ensure environmental safety. Automated sample preparation methods can streamline analysis, reduce human error, and lower operational costs.

Objectives and overview

This study demonstrates an automated solid-phase extraction (SPE) workflow for isolating six priority phthalates from large-volume drinking water samples at parts-per-billion (ppb) levels. The goals are to compare disk- and cartridge-based SPE, assess recovery and precision, and illustrate integration with gas chromatography for routine laboratory use.

Methodology and instrumentation

The core of the procedure is the Dionex AutoTrace 280 SPE system, capable of unattended processing of up to six samples (20 mL to 20 L) per run using normal- or reversed-phase cartridges and 47 mm disks. Sample pretreatment includes addition of sodium thiosulfate and a phthalate standard. SPE conditioning and loading use solvent rinses (dichloromethane, methanol) and deionized water, followed by sample loading (1.2 L) and drying under positive pressure.

Instrumentation used

• Dionex AutoTrace 280 SPE instrument with Thermo Scientific SolEx SPE 6 mL C-18 cartridges and 3M Empore 47 mm C-18 disks
• Milli-Q deionized water system
• Gas Chromatograph with Electron-Capture Detector (GC-ECD)
• Thermo Scientific TraceGOLD TG-1MS GC column

GC-ECD conditions: splitless injection at 250 °C, nitrogen makeup gas, constant flow 1.5 mL/min, oven ramp from 100 °C to 320 °C.

Main results and discussion

The disk-based SPE method delivered recoveries between 89 % and 113 % for all six phthalates, with relative standard deviations (RSDs) below 17 %. Cartridge-based extraction yielded acceptable recoveries for most analytes but showed low recovery (49 %) and high variability (RSD 39 %) for diisononyl phthalate (DINP). These data support selection of the 47 mm disk format for regulatory compliance with U.S. EPA Method 506. Automated positive-pressure loading and elution ensured consistent flow rates and minimized solvent usage.

Benefits and practical applications

• Unattended operation accelerates sample throughput: six samples ready in 2–3 hours with just 15 minutes of operator time
• Reduced solvent consumption and exposure by closed-system handling
• Improved precision and reproducibility through automated loading and elution
• Compatibility with U.S. EPA drinking water methods facilitates regulatory compliance

Future trends and potential applications

Advances in automated SPE could include integration with online evaporation and direct interfacing to mass spectrometry, further reducing manual intervention. Adoption of greener sorbents and miniaturized formats may decrease solvent demand. Extensions to other organic contaminants and coupling with high-resolution MS will broaden the scope of automated environmental analysis.

Conclusion

The Dionex AutoTrace 280 SPE instrument provides an efficient, reproducible, and regulatory-compliant approach for extracting phthalate esters from drinking water. Disk-based SPE delivers superior recovery and precision, lowering cost and labor while safeguarding analyst safety. This automated workflow supports high-throughput monitoring of trace contaminants in environmental and quality-control laboratories.

References

U.S. EPA Method 506 for determination of phthalates in drinking water by SPE and GC-ECD.