Sulfur isotope fractionation analysis in mineral waters using an Agilent 8900 ICP-QQQ

Importance of the Topic

The analysis of sulfur isotope fractionation provides insight into geological processes, water source characterization and anthropogenic impact on the sulfur cycle.

Objectives and Study Overview

This study evaluates the performance of the Agilent 8900 ICP-QQQ for low-level 34S/32S isotope ratio analysis in mineral, river, spring and seawater samples.

Methodology and Instrumentation

Certified reference materials IAEA-S-1 and IAEA-S-2 were dissolved in dilute HNO3 and diluted to 0.5 ppm S in a matrix of 50 ppm Ca and 100 ppm NaCl. Natural water samples were diluted by factors between 10 and 50000 to achieve 0.2–0.8 ppm S. Sample-standard bracketing with IAEA-S-1 was used to correct mass bias. A consistent diluent minimized matrix effects. Concentration matching allowed 32S measurement in analog mode and 34S in pulse counting mode, avoiding detector dead-time errors.

Instrumentation

Analysis was performed on an Agilent 8900 ICP-QQQ (#100 Advanced Applications configuration) with Ni cones, x-lens and a PFA nebulizer. Key parameters included RF power 1550 W, nebulizer gas 0.90 L/min, makeup gas 0.30 L/min, and oxygen cell gas at 0.45 mL/min. The MS/MS mass-shift mode reacted S+ with O2 to form SO+ (m/z 48 and 50). Integration times were 1 s (32S) and 5 s (34S), with 1000 sweeps and 10 replicates.

Main Results and Discussion

• Synthetic blends spanning δ34S −0.3 to +22.6‰ exhibited excellent linearity (R2≈1) and precision of 0.1–0.2‰ (2σ).
• Distinct δ34S signatures were observed in mineral waters, river CRM, spring water, seawater CRM and high-purity acid; seawater CRM yielded +21.5‰, matching the reference +21‰.
• High sensitivity (BEC <100 ppt) and low background enabled direct matrix dilution without cleanup.
• MS/MS mass-shift effectively removed O2+ and 16O18O+ interferences for accurate isotope measurement.

Benefits and Practical Applications

• Rapid isotopic fingerprinting of water sources for provenance and environmental monitoring.
• Detection of natural and anthropogenic sulfur inputs to ecosystems.
• Reduced sample preparation time by avoiding complex matrix removal.

Future Trends and Opportunities

• Extension of ICP-QQQ isotope ratio methods to other challenging elements.
• High-throughput screening of environmental and food samples for origin verification.
• Integration with geospatial models to map sulfur cycling dynamics.

Conclusion

The Agilent 8900 ICP-QQQ in MS/MS mode with O2 cell gas delivers a rapid, sensitive and accurate method for 34S/32S isotope ratio analysis in waters, supporting diverse applications in geochemistry, food authenticity and environmental monitoring.

References

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6. Nakano K. Agilent Application Note 5991-6852EN (2016)