Determination of Perchlorate in Vegetation Samples Using Accelerated Solvent Extraction and Ion Chromatography

Importance of the Topic

Perchlorate is a persistent, water-soluble anion that has contaminated drinking, ground and surface waters, as well as vegetation, primarily near military, propellant and fireworks manufacturing sites. Its interference with iodide uptake by the thyroid gland poses human health risks, prompting regulatory attention and state-level action limits for drinking water.

Objectives and Study Overview

This work evaluates an automated, water-based accelerated solvent extraction (ASE) method coupled with ion chromatography (IC) for the determination of perchlorate in complex solid matrices, including soil, milk and various plant tissues (alfalfa, spinach, melon, corn). The study aims to achieve low-ppb quantification with high recoveries and minimal manual cleanup.

Methodology and Instrumentation

Samples (~3–5 g) were spiked with perchlorate, mixed with ASE Prep DE diatomaceous earth and loaded into stainless steel extraction cells. In-cell cleanup combined Dionex OnGuard ion-exchange resins (H+, Ag+, Ba2+, RP) and basic alumina to remove co-extractives. Extractions were performed at 80 °C and 1500 psi for three static cycles of 5 min each, followed by water flush and nitrogen purge. Extracts were filtered (0.2 µm) and analyzed by IC using a NaOH eluent gradient (0.5–65–100 mM) and suppressed conductivity detection.

Used Instrumentation

• Dionex ASE 200/300 Accelerated Solvent Extractor
• Thermo Scientific Dionex ICS-2500 IC system with GP50 pump, EG50 eluent generator and AS40 autosampler
• IonPac AS16 analytical column, AG16 guard column and Cryptand C1 preconcentration column
• ASRS ULTRA II suppressor and CD25 conductivity detector

Main Results and Discussion

Recoveries at 10, 50 and 200 ng/g spikes in melon, corn and spinach ranged from 88.7 % to 118.7 % with RSDs below 9 %. Soil and milk matrices showed similar performance. Method detection limits (MDLs) of 0.7–2.0 µg/kg and reliable quantitation limits (RQLs) of 2.9–8.0 µg/kg were achieved. In-line cleanup markedly reduced chloride/sulfate interferences, enabling direct injection of ASE extracts.

Benefits and Practical Applications

• Rapid, fully automated extraction and cleanup with minimal solvent use
• High throughput: up to 24 samples per run without manual intervention
• Direct IC analysis of clean extracts, eliminating SPE or additional cleanup
• Reliable low-ppb quantification of perchlorate in vegetation and soil for environmental monitoring and food safety testing

Future Trends and Opportunities

Further integration of ASE with on-line preconcentration and multi-mode detection (e.g., mass spectrometry) could push detection limits lower. Expansion to other emerging anionic contaminants and diverse biosolid matrices will broaden applicability. Continuous development of resin and sorbent materials may improve selectivity and simplify workflows.

Conclusion

The ASE-IC method offers a fast, robust and reproducible approach for perchlorate analysis in complex solid samples. In-cell cleanup with ion-exchange resins and alumina delivers clean extracts suitable for direct IC injection, achieving recoveries near 100 % and low-ppb detection limits while reducing solvent, labor and analysis time.

Reference

• Cheng Q. et al., Talanta, 2005.
• Jackson W.A. et al., J. Agric. Food Chem., 2005, 53, 369.
• U.S. EPA Method 314.1: Preconcentration/Matrix Elimination IC with Suppressed Conductivity, 2005.
• Richter B., Murphy B., Thermo Fisher Scientific Application Note 356, 2012.