China Soil Pollution Survey: Elemental Analysis of Soil and Sediment Digests by ICP-MS

Importance of the Topic

Soil and sediment contamination by heavy metals and metalloids is a critical public health and environmental challenge worldwide. Rapid industrialization, intensive agriculture, mining, and improper waste disposal introduce toxic elements into ecosystems, threatening water quality, food safety, and biodiversity. Reliable multi-element analysis is essential to map contamination levels, guide remediation strategies, and enforce regulatory standards.

Objectives and Study Overview

This study aimed to establish and validate a high-throughput analytical workflow for quantifying 16 elements in soil and sediment digests in support of China’s national soil pollution survey. The focus was to combine an optimized low-pressure microwave digestion protocol with the Agilent 7800 ICP-MS—equipped with High Matrix Introduction (HMI) and a helium collision cell—to demonstrate accurate, sensitive, and rapid analysis compliant with the Technical Stipulation of Soil Analysis for China Soil Pollution Survey.

Methodology and Used Instrumentation

A two-step low-pressure microwave digestion, capable of processing 30 samples per batch, was performed using an Ethos One system (Milestone). The digest mixture comprised HNO₃, HCl, H₂O₂, and HF neutralized by H₃BO₃, yielding final total dissolved solids of ~0.3%. Analytical measurements were carried out on an Agilent 7800 ICP-MS with HMI aerosol dilution, ORS4 collision cell in He mode, Ni cones, and standard glass/quartz sample introduction. An SPS 4 autosampler delivered samples along with online internal standards (⁶Li, ⁷⁴Ge, ¹⁰³Rh, ¹¹⁵In, ¹⁸⁵Re). Calibration employed six matrix-matched standards, and quality control included initial, periodic, and low-level verification checks as per Chinese guidelines.

Main Results and Discussion

• Calibration curves for major and trace elements exhibited excellent linearity (R²>0.9999).
• Method detection limits of 0.001–0.228 µg/L (0.001–0.114 mg/kg) surpassed regulatory requirements.
• Internal standard recoveries remained stable within ±30% over 109 runs spanning 7 hours, indicating minimal drift or matrix buildup.
• Continuing calibration verifications consistently met ±10% recovery, with low-level checks within ±30%.
• Matrix spike recoveries at 50 ppb were within ±20%, confirming method accuracy.
• Analysis of five sediment and eight soil certified reference materials (CRMs) yielded mean recoveries of 83–123% relative to certified values for all elements.

Benefits and Practical Applications

• HMI allows direct introduction of low-dilution digests, reducing preparation time, contamination risk, and detection limit compromise.
• Helium collision mode efficiently removes polyatomic interferences under a single condition, simplifying method development.
• The 7800 ICP-MS offers a wide dynamic range, enabling simultaneous quantification of major (ppm–wt%) and trace (ppt) elements in one run.
• The streamlined digestion and analysis workflow supports large-scale environmental surveys and routine QA/QC in industrial and governmental laboratories.

Future Trends and Opportunities

Emerging technologies such as discrete sampling systems (e.g., ISIS 3) can further increase throughput by overlapping rinse and measurement steps. Analytical scope may expand to include critical technology metals (e.g., rare earth elements) as emerging contaminants. Integration of automated data processing, cloud-based quality control, and real-time mapping tools will enhance the efficiency and responsiveness of environmental monitoring programs.

Conclusion

The combination of low-pressure microwave digestion and Agilent 7800 ICP-MS with HMI and He collision cell delivers a robust, precise, and efficient solution for comprehensive multi-element analysis of soil and sediment samples. The validated method meets stringent survey requirements, maintains excellent stability over extended runs, and provides reliable data to support environmental assessment and remediation efforts.

References

• Environmental Development Centre of Ministry of Environmental Protection. Technical Stipulation of Soil Analysis for China Soil Pollution Survey, 2017.
• Kubota, T. Simple and Reliable Soil Analysis using the Agilent 7800 ICP-MS with ISIS 3, Agilent Technologies, 2017, publication 5991-8674EN.
• Yamanaka, K., Wilbur, S. Maximizing Productivity for High Matrix Sample Analysis using the Agilent 7900 ICP-MS with ISIS 3, Agilent Technologies, 2014, publication 5991-5208EN.