Analysis of Soil

Significance of the topic

Soil contamination by heavy metals and toxic elements presents significant risks to public health and the environment. Regulatory frameworks such as the Soil Contamination Countermeasures Law establish maximum concentration standards and drive the need for robust analytical techniques. Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) enables sensitive, multi‐element quantification essential for risk assessment and remediation planning.

Objectives and overview of the study

This study evaluates the quantitative performance of the ICPE-9000 multi‐type ICP‐AES system for analyzing soil contaminants. It compares two sample preparation approaches—acid dissolution (official HCl method) and total decomposition (microwave‐assisted digestion)—and benchmarks results against certified reference materials and ICP‐MS data to verify accuracy and precision.

Methodology and instrumentation

The investigation employed two soil standards (NIST SRM2710 and SRM2711) and a volcanic ash soil reference (JSAC0411). Two digestion protocols were applied:

• Official HCl dissolution: 6 g soil dissolved in 200 mL of 1 M HCl (with buffer for Cr VI), filtered, then acidified and boiled to 20 mL before dilution.
• Total decomposition: Microwave high‐pressure digestion of 0.2 g sample with HNO₃, H₂O₂ and HF followed by evaporation and nitric acid treatment.

Instrumentation used:

• Shimadzu ICPE-9000 ICP‐AES (axial view, coaxial nebulizer, cyclone chamber, mini torch).
• Shimadzu ICPS-8100 high‐resolution sequential ICP‐AES for spectral interference comparison.
• Shimadzu ICP-MS (ICPM-8500) for method validation.

Main results and discussion

Quantitative analysis demonstrated:

• Microwave digestion matched certified values for most elements (Cd, Pb, Cr, As, Hg, B) when compared to NIST SRM2711; HCl dissolution underestimated elements like Cr and Hg due to incomplete decomposition.
• High‐resolution ICP resolved spectral overlaps (e.g., As interference on Cd at 228.802 nm) more effectively than the multi‐type ICPE-9000, although inter‐element correction in ICPE-9000 improved accuracy.
• Calibration curves exhibited excellent linearity (r ≥ 0.9999) for trace to high‐concentration ranges, enabling reliable quantitation down to sub‐mg/kg levels.
• Spike and recovery tests on JSAC0411 showed recoveries between 93 % and 108 %, demonstrating method robustness.

Benefits and practical applications

The ICPE-9000 ICP‐AES system offers:

• Simultaneous multi‐element analysis with wide dynamic range, covering regulatory limit monitoring to trace‐level contaminants.
• High throughput for routine soil screening in environmental laboratories, redevelopment projects, and site risk assessments.
• Ability to apply inter‐element correction to mitigate spectral interference without resorting to ultra‐high resolution equipment.

Future trends and opportunities

Advances in ICP‐AES will focus on:

• Enhanced spectral resolution and data processing algorithms to further reduce interferences in complex matrices.
• Integration with hyphenated techniques (e.g., laser ablation ICP‐MS) for in situ elemental mapping and rapid screening.
• Automation of sample preparation and on‐line calibration for real‐time monitoring in field applications.

Conclusion

This study confirms that the ICPE-9000, combined with appropriate digestion methods and inter‐element correction, provides accurate, sensitive, and efficient soil contaminant analysis. Microwave total decomposition yields results closest to certified values, while the official HCl method remains suitable for bioavailability‐based risk assessments. Overall, ICP‐AES stands as a reliable tool for environmental monitoring and regulatory compliance.

Reference

• Environmental Quality Standards for Soil (Ministry of Environment Notification No.46, 1991)
• Soil Contamination Countermeasures Law, Enforcement Regulation (Ministry of Environment Ordinance No.29, 2002)
• Measurement Methods for Soil Dissolution Test (Ministry of Environment Notification No.18, 2003)
• Measurement Methods for Soil Content Test (Ministry of Environment Notification No.19, 2003)
• EPA Method 3052: Microwave Assisted Acid Digestion of Siliceous and Organically Based Matrices