Simple, Reliable Analysis of High Matrix Samples According to US EPA Method 6020A ICP-MS

Significance of the Topic

High‐matrix environmental samples present substantial challenges for trace metal analysis due to varying dissolved solids, polyatomic interferences and unknown sample composition. US EPA Method 6020A provides a versatile protocol for quantifying sub‐µg/L concentrations of multiple elements in water, waste extracts and digests without imposing restrictions on advanced ICP‐MS technologies. Integrating helium collision cell technology and high matrix introduction simplifies interference removal and enhances robustness, enabling reliable routine analysis of diverse environmental matrices.

Objectives and Study Overview

This application note demonstrates the capability of the Agilent 7700x ICP‐MS to meet EPA Method 6020A requirements across a broad range of matrices and analyte concentrations. A 15‐hour, 156‐run sequence mimicked a contract laboratory workload, encompassing reference waters, soil and sediment standards, synthetic seawater and spikes. Key performance metrics include method detection limits, dynamic range, calibration stability, precision, accuracy and long‐term robustness in high total dissolved solids (TDS) samples.

Methodology

All analyses followed EPA 6020A guidelines:

• Single initial calibration covering 0.1–100 ppb for trace elements, 10–10 000 ppb for minerals and 0.01–2 ppb for Hg
• Automatic continuing calibration blanks (CCB) and verification standards (CCV, LLCCV) after every 10 samples
• Sample sequence: NIST 1643e water, soil and sediment CRMs at 1/10 and 1/50 dilutions, synthetic and spiked seawater
• Low‐level standard replicates for method detection limit (MDL) determination
• Periodic matrix spikes and duplicates in 1/10 seawater to assess matrix tolerance

Instrumentation Used

The Agilent 7700x ICP‐MS was operated under robust plasma conditions (<1 % CeO/Ce) with integrated High Matrix Introduction:

• Helium collision cell mode for universal polyatomic interference removal
• No‐gas mode for elements free of common interferences
• High Matrix Introduction system to minimize matrix suppression
• Continuous internal standard monitoring to ensure >70 % recovery

Main Results and Discussion

Method detection limits were predominantly in the single‐digit ppt to low ppb range, well below typical regulatory requirements. Dynamic range spanned 2 ppt to >120 ppm without additional dilutions. Continuing calibration verification recoveries remained within ±10 % for all elements over 15 hours. Low‐level CCV recoveries were ±10 % with RSDs <5 %. Certified reference material analyses at 1/10 and 1/50 dilutions yielded recoveries of 90–110 % and RSDs <5 %. Seawater matrix spikes in 3 % NaCl showed recoveries of 88–105 % and RSDs <6 %, confirming excellent suppression control and stability. Internal standard signals stayed above 70 % throughout, with only one recalibration event needed for cone conditioning.

Benefits and Practical Applications

The described approach delivers:

• Universal interference removal using He mode without correction equations
• Wide dynamic range accommodating trace to mineral elements
• High throughput of mixed unknown samples with minimal reruns
• Enhanced long‐term stability in complex, high‐TDS matrices
• Simplified compliance with EPA 6020A for environmental laboratories

Future Trends and Applications

Advancements in collision/reaction cell chemistries and high matrix introduction will further streamline analysis of emerging contaminants in challenging matrices. Integration with automated sample preparation and real‐time data quality monitoring can extend applicability into industrial process control, food safety and clinical bioanalysis. Continued development of robust plasma sources and novel cell gases promises to expand detectable element lists and lower detection limits.

Conclusion

The Agilent 7700x ICP‐MS, leveraging helium collision technology and high matrix introduction, fulfills US EPA Method 6020A requirements for reliable, accurate, high‐throughput analysis of diverse environmental samples. Robust interference removal, broad dynamic range and long‐term stability enable contract and research laboratories to process unknown high‐matrix samples in a single sequence without extensive prior knowledge or repeated calibrations.

References

1. US EPA. Method 6020A Revision 4, Determination of Trace Elements by ICP‐MS. February 2007.
2. Wilbur S, Soffey E. Meeting Worldwide Regulatory Requirements for the Analysis of Trace Metals in Drinking Water Using the Agilent 7500c ICP‐MS. Agilent Technologies Application Note 5988-8902EN, 2005.
3. Wilbur S, Jones C. Simple, Reliable Analysis of High Matrix Samples According to US EPA Method 6020A ICP‐MS. Agilent Technologies, 2021;5990-5514EN.