Handbook of ICP-QQQ Applications using the Agilent 8800 and 8900

Significance of the topic

Advances in high-purity rare earth element (REE) materials underpin many cutting-edge technologies, from permanent magnets to advanced optics. Controlling REE purity to parts-per-billion levels ensures optimal performance in applications such as lasers, catalysts and electronic devices. However, direct spectroscopic analysis of trace REE impurities in a dominant REE matrix is challenged by strong polyatomic overlaps arising from metal-oxide and metal-hydride species.

Objectives and overview

This study demonstrates the direct determination of trace REE impurities in high-purity lanthanide oxide matrices (Ce₂O₃, Pr₆O₁₁, Nd₂O₃, Gd₂O₃, Sm₂O₃, Eu₂O₃, Tb₄O₇, Dy₂O₃, Er₂O₃, Yb₂O₃) using an Agilent 8900 triple quadrupole ICP-MS (ICP-QQQ). The goal was to resolve challenging spectral interferences and achieve sub-ppb background equivalent concentrations (BECs) for all REE analytes in a 500 ppm matrix solution.

Methodology

An MS/MS approach was employed, combining two quadrupole mass filters (Q1 and Q2) separated by an octopole reaction cell. Reactive cell gases (O₂ and NH₃) were evaluated to selectively convert analyte ions to oxide (MO⁺) or suppress hydride interferences. Q1 rejects all non-target masses entering the cell, ensuring controlled reaction chemistry and preventing formation of unwanted product ions.

Instrumentation

Agilent 8900 ICP-QQQ configured for Advanced Applications, with standard quartz interface, PFA nebulizer, and Pt-tipped cones. Preset “general-purpose” HMI plasma conditions were used. Cell tuning parameters included O₂ mass-shift mode (0.35 mL/min O₂, –5 V octopole bias, –8 V KED) and NH₃ on-mass and mass-shift modes (10% NH₃ in He, 1–8 mL/min, –18 V bias, –7 V KED).

Main results and discussion

Analysis in no-gas and He collision modes revealed high BECs (ppb to multi-ppb) for mid- and high-mass REEs due to REE-derived oxide and hydroxide interferences. O₂ MS/MS mass-shift mode reduced BECs by 10²–10⁵× for interfered elements (Tb, Dy, Ho, Er, Tm, Yb, Lu), down to the ppt range. NH₃ on-mass mode further suppressed residual overlaps on Dy and Ho, improving BECs by a factor of ~20× relative to O₂ mode. NH₃ mass-shift mode achieved the lowest BEC (0.022 ppb) for Tb in a Nd matrix by measuring TbNH⁺ clusters.

Practical applications

• Rapid, direct quantification of REE impurities in single-element REE oxides.
• Elimination of time-consuming separation steps such as ion-exchange or chelating resins.
• Quality control for REE material manufacturers, ensuring sub-ppb purity.
• Improved reliability in high-technology applications dependent on REE performance.

Future trends and potential uses

• Expansion to online process monitoring of REE refining streams using ICP-QQQ.
• Integration with laser ablation sampling for solid-state REE mapping.
• Development of MS/MS methods for isotopic ratio analysis in nuclear forensics.
• Application of reactive gas libraries to further extend interference removal in complex matrices.

Conclusion

The Agilent 8900 ICP-QQQ MS/MS method with O₂ and NH₃ reaction gases provides robust, trace-level analysis of REE impurities in high-purity oxide matrices. By effectively removing oxide and hydride interferences, BECs were reduced to sub-ppb levels across 13 REEs. This approach offers a direct, high-throughput alternative to traditional separation methods, enabling precise quality control in REE manufacturing and advanced materials research.