Determination of Lanthanide Metals in Digested Rock Samples by Chelation Ion Chromatography

Significance of the Topic

The accurate determination of trace lanthanide elements in geological samples is central to mineral exploration, geochemical fingerprinting and environmental monitoring. Complex rock matrices contain high levels of major elements and transition metals that challenge traditional detection methods, leading to high costs and extensive sample pretreatment. Chelation ion chromatography (chelation IC) offers an integrated solution combining selective pre-concentration, matrix elimination and high-resolution separation, reducing analysis time and improving detection limits for lanthanides in digested rock samples.

Objectives and Study Overview

This work presents the development and validation of a chelation IC technique for quantifying lanthanide series elements in dissolved rock matrices. Key goals included: establishing selective removal of alkali, alkaline earth and interfering transition metals; optimizing a chelating concentrator for trace lanthanide retention; integrating an automated sample pretreatment module with an ion chromatography system; and demonstrating accuracy through spike-recovery tests and analysis of USGS basalt, andesite and peridotite geochemical reference materials.

Methodology and Used Instrumentation

Reagents and sample pretreatment rely on controlled chelation and pH adjustment steps using ammonium acetate, nitric acid, hydrochloric acid/ethanol mix and ammonium nitrate. The automated system combines:

• Two quaternary Dionex Advanced Gradient Pumps (AGP) for chelation concentration and analytical elution
• Sample Concentration Module with dual high-pressure pumps and multiport selector valves
• Chelating concentrator column (MetPac CC-1) and transition-metal cleanup column (TMC-1)
• Analytical IonPac CS5 separation column with post-column 4-(2-pyridylazo)resorcinol derivatization
• Variable wavelength UV–Vis detector at 520–530 nm, data acquisition via ACI/AI-450 workstation

Key operational steps include sample loading and buffering, selective elution of matrix components, tight band concentration of lanthanides, cleanup of transition metals, column regeneration and final chromatographic separation of metal–chelator complexes.

Main Results and Discussion

Spike/recovery experiments in peridotite matrix showed recoveries of 90–115% across the lanthanide series at sub-ppm levels. Analysis of USGS BHVO-1 basalt and AGV-1 andesite reference materials yielded results within 10% of recommended values for La through Yb. Chromatograms exhibited baseline stability, minimal interferences and total run time under 40 minutes. The membrane reactor reduced detection limits by fivefold compared to conventional mixing.

Benefits and Practical Applications

Chelation IC streamlines the analysis of lanthanide elements in mineral, environmental and industrial samples by:

• Reducing sample pretreatment time from hours to minutes
• Minimizing matrix interferences without complex open-column protocols
• Lowering detection limits to sub-ppb levels
• Offering automated, reproducible workflows suitable for high-throughput laboratories

Future Trends and Opportunities

Emerging opportunities include coupling chelation IC with mass spectrometric detection for isotopic analyses, extending applicability to heavy metals in biological and environmental matrices, and refining chelating resins for even greater selectivity. Integrating on-line dilution, multi-element detection and advanced data processing will further enhance throughput and analytical robustness.

Conclusion

The developed chelation ion chromatography method provides a rapid, sensitive and interference-free approach for trace lanthanide determination in complex rock digests. Validation against certified reference materials confirms its accuracy and precision. This technique offers a practical and cost-effective alternative to traditional spectrometric methods, with broad applicability in geochemistry, resource evaluation and environmental analysis.