Reliable analysis of soil samples for environmental monitoring using triple quadrupole ICP-MS

Significance of the topic

Reliable determination of elemental composition in soils is crucial for environmental monitoring, ecological risk assessment and compliance with regulatory standards. Advanced multi-element techniques help track pollutant distribution, assess remediation efficacy and support policy decisions.

Objectives and study overview

This study evaluates the performance of the Thermo Scientific iCAP TQe triple quadrupole ICP-MS using oxygen as the sole reactive gas and argon gas dilution for soil sample analysis. The goal is to demonstrate simplified interference removal, improved sensitivity, and high throughput across diverse soil and sludge matrices, including certified reference materials.

Methodology and instrumentation

• Sample preparation: Microwave-assisted digestion of 0.1 g soil in aqua regia (HCl, HNO3, H2O2), diluted to 50 mL with ultrapure water; eight soil and sludge types, including three CRMs.
• Instrument setup: iCAP TQe ICP-MS with quartz cyclonic spray chamber (2.7 °C), Micromist nebulizer (400 µL/min), quartz torch, nickel interface cones; QCell in TQ-O2 mode with O2 (0.2 mL/min) and argon gas dilution (55 %, 1000 mL/min).
• Autosampler: iSC-65 with Step Ahead feature (10 s overlap) enabling continuous runs and over 300 samples per day.
• Calibration and QC: Seven-point multielement calibration (0.002–100 mg/L in 2 % HNO3) with online addition of Ge, Rh, Re internal standards; QC standards measured every 15 samples.
• Detection limit assessment: Ten reagent blanks analyzed to calculate 3σ detection limits, comparing TQ-O2 and KED modes.

Key results and discussion

• Linearity: All elements displayed calibration correlation coefficients above 0.999.
• Detection limits: TQ-O2 mode achieved lower DLs versus single-quadrupole KED, notably for As (1 vs 7 ng/L), Cd (0.003 vs 0.6 ng/L) and Se (5.7 vs 22940 ng/L for 80Se).
• Throughput and stability: Continuous 12 h run analyzed >300 samples at 2 min 41 s per sample; QC recoveries remained within 86–113 %.
• Internal standard performance: Recoveries of Ge, Rh and Re stayed between 82–108 %, confirming matrix tolerance and signal stability.
• CRM accuracy: Certified reference materials (NIST 2702, NIST 2709a, NRCC PACS-2) yielded recoveries between 86–113 % across sub-ppm to thousands ppm levels.

Benefits and practical applications

• Single-mode operation with only oxygen simplifies method development and reduces total analysis time by avoiding mode switching.
• Advanced interference removal ensures accurate quantification of challenging analytes in complex matrices without extensive sample dilution.
• High sample throughput and robust performance suit environmental testing laboratories handling large batches.
• Argon gas dilution enhances matrix tolerance, eliminates manual dilutions and reduces contamination risk.

Future trends and potential applications

Emerging developments may include full automation of sample preparation, coupling with data analytics for large-scale environmental surveillance, and extending the single-reactive-gas approach to other challenging matrices such as biological fluids and industrial wastes. Remote monitoring and real-time field deployments could further broaden application scope.

Conclusion

The Thermo Scientific iCAP TQe ICP-MS with oxygen reaction gas and argon gas dilution delivers rapid, sensitive, and accurate multi-element soil analysis. Its ability to maintain stability and meet regulatory requirements over extended runs makes it a powerful tool for routine environmental monitoring and research.