WCPS: Direct Metal Analysis by New Galvano-Mirror fs-LA-ICP-MS using 100%-Normalization Method with NIST 612 Glass CRM as Calibration Standard

Significance of the Topic

The precise quantification of metals and alloys is critical in fields ranging from materials science to quality control in industry. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) offers a direct solid-sampling approach that avoids time-consuming digestion steps and reduces contamination risks. However, calibration remains a key challenge, especially when matrix-matched standards are unavailable. The development of robust methods combining non-matrix matched glass standards with novel normalization strategies and femtosecond laser ablation can greatly enhance the accuracy and versatility of solid-sample analysis.

Objectives and Study Overview

This work evaluates a new calibration protocol for the direct analysis of metal alloys and pure metals using femtosecond LA-ICP-MS. Key goals include:

• Demonstrating the 100% normalization method with NIST 612 glass standard to compensate for differences in ablation yield between the glass standard and metal samples.
• Assessing the reduction of elemental fractionation by employing a galvano-mirror scanned, high-repetition-rate femtosecond laser (fsLA).
• Validating the approach through quantitative analysis of three certified reference metal materials.

Methodology and Instrumentation

A dual approach was adopted:

• 100% normalization: Total concentrations of all measured elements are adjusted to a sum of 100% using a built-in function in the MassHunter software. This corrects for variances in ablation rates between the sample and calibration standard.
• Femtosecond laser ablation: Ultrashort pulses (290 fs, 257 nm) minimize thermal effects and melt-induced fractionation, yielding particles representative of the bulk metal.

Used Instrumentation

• Agilent 8900 Triple Quadrupole ICP-MS in Advanced Applications configuration.
• RAIJINα fsLA system (Seishin Trading) with galvano-mirror scanning, 30×30 mm scan area, and up to 60 kHz repetition rate.

Operating parameters (selected): spot size 10 µm, repetition rate 20 kHz, ablation depth ~8 µm, carrier gas Ar (1.0 L/min) and He (3.0 mL/min), fluence 5–7 J/cm2.

Main Results and Discussion

Three metal CRMs were analyzed: an Al/Mg alloy (BAM 310), a nickel alloy (NIST 1249), and pure copper (ERM-EB385). Key findings:

• Recoveries of certified elements generally fell within 80–120%, demonstrating high accuracy across trace to major element concentrations.
• Half-mass correction for 48Ti++ interference on 24Mg in NIST 1249 yielded accurate Mg quantification.
• Multi-tune approach reduced detector overload for 63Cu in pure copper CRM, with normalization maintaining consistent calibration.

The combined normalization and fsLA approach effectively mitigated both ablation yield discrepancies and fractionation artifacts, enabling reliable use of a single non-matrix matched standard.

Practical Benefits and Applications

This methodology offers:

• Streamlined calibration workflows by avoiding the need for multiple matrix-matched standards.
• Enhanced throughput and reduced reagent use by eliminating wet chemistry sample preparation.
• Broad applicability to conductive and non-conductive materials, including hard-to-digest alloys and ceramics.

Future Trends and Potential Applications

Advances likely to expand the technique’s reach include:

• Integration of automated normalization algorithms with real-time data processing.
• Further development of ultrafast laser sources and beam scanning to increase spatial resolution and sensitivity.
• Extension to more complex multi-phase materials and in situ analysis in manufacturing environments.

Conclusion

The study demonstrates that combining a 100% normalization calibration method with femtosecond LA-ICP-MS provides an accurate, efficient, and versatile platform for direct solid analysis of metals and alloys. By leveraging a well-characterized glass standard and minimizing fractionation effects, the approach simplifies calibration and expands the practical utility of LA-ICP-MS in quality control and research.

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