Determination of trace elements in steel using the Agilent 7900 ICP-MS

Significance of the topic

The control of trace element impurities in steel and alloys is critical for ensuring mechanical properties, corrosion resistance and overall performance of metal components. As modern engineering demands ever higher purity and tighter specifications, analytical methods with lower detection limits and robust handling of complex sample matrices become essential.

Objectives and study overview

This work aims to develop and validate a method for quantifying a broad range of elements in steel digests using the Agilent 7900 ICP-MS equipped with Ultra High Matrix Introduction (UHMI). The method is benchmarked against ASTM and JIS standards and demonstrated on certified reference materials.

Methodology

Steel samples were digested following a modified JIS G1258 procedure. A 0.5 g sample was pre-digested in 12 mL of a 1:1:1 HNO₃/HCl/UPW acid mix, heated to 200 °C, cooled and diluted to 100 g. Calibration standards were prepared in the same acid matrix without added iron. A mixed internal standard (Sc, Y, Tb) was introduced on-line. The peristaltic pump speed was fixed at 0.1 rps to ensure consistent sample and standard uptake.

Instrumentation

• Agilent 7900 ICP-MS with standard nickel sampling and skimmer cones
• Quartz glass concentric nebulizer and spray chamber
• Quartz torch with 2.5 mm injector
• ORS4 collision/reaction cell (He, HE-He and H₂ modes)
• Ultra High Matrix Introduction aerosol dilution system
• Agilent ASX-520 autosampler

Main results and discussion

• Calibration linearity for all analytes (10 ppb–10 000 ppb) achieved R² > 0.9999 across He, HE-He and H₂ cell modes.
• Method detection limits (3σ blanks) ranged from 0.002 to 1.7 mg/kg, meeting or exceeding ASTM/JIS quantitation requirements and surpassing typical ICP-OES performance.
• Analysis of SRM NIST 2165 showed recoveries between 93 % and 106 % for certified elements; spike recoveries (100 ppb) of non-certified elements fell within 95 %–105 %.
• Two Japanese Steel Standard CRMs (JSS 152-5 and JSS 168-2) were measured with excellent agreement to reference values, demonstrating robustness across steel grades.
• Six-hour continuous measurement of a 0.5 % Fe matrix spiked with P (500 ppb), Si (2 ppm) and trace elements (100 ppb) yielded RSD < 3 %, confirming minimal signal drift due to UHMI dilution.

Benefits and practical applications

• High matrix tolerance allows direct analysis of 0.5 % TDS steel digests without matrix-matched standards.
• Wide dynamic range (11 orders of magnitude) enables simultaneous measurement of major and trace elements in a single run.
• Lower detection limits facilitate stricter quality control in high-performance alloys and high-purity steels.
• Simplified sample preparation and improved plasma stability reduce downtime and maintenance.

Future trends and applications

The UHMI approach is poised to expand ICP-MS use in other challenging matrices such as soils, salts and complex industrial digests. Continued advances in aerosol dilution and collision/reaction cell chemistries will further lower interferences and detection limits, supporting next-generation materials analysis and regulatory compliance.

Conclusion

The Agilent 7900 ICP-MS with UHMI and ORS4 effectively addresses the challenges of high-matrix steel sample analysis. The method delivers excellent accuracy, sensitivity and stability, aligning with ASTM and JIS standards and outperforming conventional techniques for trace element determination in steel.

Reference

1. Yamanaka K and Wilbur S. Maximizing productivity for high matrix sample analysis using the Agilent 7900 ICP-MS with ISIS 3 discrete sampling system. Agilent Technologies publication 5991-5208EN (2014).
2. Proper W, McCurdy E and Takahashi J. Performance of the Agilent 7900 ICP-MS with UHMI for high salt matrix analysis. Agilent Technologies publication 5991-4257EN (2014).
3. Cheng Y. Procedia Engineering, 24, 447–453 (2011).
4. Tran TN. Analysis of Metals in High Alloy Steel by ICP-OES. Agilent Technologies publication ICPES-6 (2010).