Content Analysis of Heavy Metals in Soil by ICP-MS

Importance of Topic

Soil contamination by heavy metals can pose serious threats to human health and ecosystems. Accurate quantification of elements such as As, Cd, Cr, Pb and Se at trace levels is essential to ensure compliance with environmental regulations and to assess the effectiveness of remediation efforts. High sensitivity, minimal interference and stable performance are key requirements for reliable soil analysis.

Objectives and Study Overview

This work evaluates the performance of the ICPMS-2050 system for soil content testing under Japan’s Soil Contamination Countermeasures Act. The study aims to:

• Achieve detection limits below 1/100 of the soil content standard
• Assess interference from rare earth elements (REEs) on As and Se measurements
• Compare two spectral correction methods
• Verify long-term stability and reproducibility over multiple samples

Five distinct soil samples (Soil A–E) were analyzed according to standard pretreatment protocols, and results were validated by spike recovery tests.

Methodology and Instrumentation

Sample Pretreatment:

• Elements except Cr: Soil mixed with 1 mol/L HCl (3 % w/w), shaken 2 h, filtered (0.45 µm), acidified and diluted
• Cr(VI): Soil extracted with carbonate/bicarbonate buffer, shaken, filtered, oxidized with HNO3 and diluted; total Cr reported

Calibration and Standards:

• Multi-element calibration solutions spanning 1/100 of the soil standard
• Internal standards (Be, Ga, In, Tl) added automatically at 1:9 ratio

Instrument and Conditions:

• ICPMS-2050 with mini torch and cyclone chamber
• Plasma RF power 1.2 kW; gas flows: plasma 9.0 L/min, auxiliary 1.1 L/min, carrier 0.6 L/min, dilution 0.25 L/min
• Collision/reaction cell gases: He for As and most elements; H2 for Se
• Sampling depth 7 mm; peristaltic pump 15 rpm

Main Results and Discussion

Detection Limits and Quantification:

• LOQ in solution corresponds to < 1/100 of soil regulatory values for all target elements
• LOQ in soil: 0.03 mg/kg for As, 0.4 mg/kg for B, 0.005 mg/kg for Cd, 0.04 mg/kg for Cr, 0.005 mg/kg for Pb, 0.06 mg/kg for Se

Interference from REEs:

• He collision mode yields significant spectral overlap from Nd and Sm on As and from Gd on Se
• Interelement correction (IEC) and half-mass correction both reduce REE interference; half-mass correction is less affected by matrix variability
• H2 reaction gas effectively eliminates interference on Se, enabling high-sensitivity measurement

Validation and Stability:

• Spike recovery tests on soils show 98–103 % recovery across all elements
• Continuous measurement of 50 samples demonstrates intensity variation of internal standards within 88–104 %
• Quantitative values remain stable within 98–103 % after internal standard correction
• Advanced rinse function reduces carryover and shortens cycle time

Benefits and Practical Applications

• High throughput soil analysis with robust performance under regulatory requirements
• Flexible correction methods allow adaptation to sample matrix and sensitivity needs
• Reduced argon consumption with mini torch lowers operating costs
• Automated rinse and internal standard addition enhance reproducibility and workflow efficiency

Future Trends and Potential Uses

• Application of advanced collision/reaction cell chemistries to further minimize spectral interferences
• Integration with automated sample preparation and data processing for higher throughput
• Extension to other complex matrices such as sediments, sludges and biological tissues
• Development of portable or miniaturized ICP-MS systems for field screening

Conclusion

The ICPMS-2050 system delivers sensitive and reliable quantification of heavy metals in soil at levels well below regulatory standards. Effective REE interference correction, stable long-term performance and efficient sample handling make it a powerful tool for environmental monitoring and quality control in the laboratory.

Reference

1 The Ministry of the Environment Notification No. 19 Determination Method for Soil Content Survey
2 The Ministry of the Environment Notification No. 29 The Ordinance for Enforcement of the Soil Contamination Countermeasures Act