Removal of hydride ion interferences (MH+ ) on Rare Earth Elements using the Agilent 8800 Triple Quadrupole ICP-MS

Significance of the topic

The accurate measurement of rare earth elements (REEs) at trace levels is essential in geochemistry, mining and materials science. Hydride ion (MH+) interferences can compromise inductively coupled plasma mass spectrometry (ICP-MS) results, leading to positive bias in critical isotopes such as Ce in a La matrix. Overcoming these interferences is vital for quality control of high-purity REE production and reliable environmental or geological analysis.

Objectives and study overview

This study evaluates the capability of the Agilent 8800 Triple Quadrupole ICP-MS (ICP-QQQ) to remove hydride interferences on REEs. Three challenging analyte/matrix pairs were assessed:

• La measurement in a 50 ppm Ba matrix
• Ce measurement in a 50 ppm La matrix
• Tb measurement in a 50 ppm Gd matrix

The goal was to compare conventional single-quadrupole mass-shift mode with MS/MS mass-shift mode using oxygen reaction gas and to determine achievable background equivalent concentrations (BECs) and detection limits (DLs).

Methodology and instrumentation

The instrument used was an Agilent 8800 ICP-QQQ equipped with x-lens, nickel sample and skimmer cones, and a pumped PFA nebulizer for rapid washout. Q1 before the Octopole Reaction System (ORS3) cell was set as a 1 amu band-pass filter. Oxygen served as the reaction gas to convert REE ions to oxide species. Measurements followed the method of standard additions in 1% HNO₃ with standard levels of 50–200 ppt. Data were acquired in two modes:

1. Single-quad mass-shift (emulating ICP-QMS)
2. MS/MS mass-shift with strict Q1 filtering

Main results and discussion

Single-quad mass-shift mode failed to generate calibration curves at the low ppt level due to unwanted reaction products from non-target ions. In contrast, MS/MS mass-shift mode achieved:

• La in Ba: BEC 8.5 ppt, DL 2.5 ppt
• Ce in La: BEC 10.6 ppt, DL 0.8 ppt
• Tb in Gd: BEC 24.8 ppt, DL 2.0 ppt

Precursor scans fixing Q2 at m/z 156 revealed interfering precursors at m/z 138–140 forming species at m/z 156. Q1 filtering effectively removed these unwanted ions before reaction, ensuring only the target REE oxide reached the detector.

Benefits and practical applications

The ICP-QQQ in MS/MS mass-shift mode provides:

• Reliable ppt-level quantification of REEs in high-matrix samples
• Elimination of hydride interferences that cannot be resolved by high-resolution ICP-MS
• Improved predictability of reaction chemistry by rejecting non-target ions before the cell

This approach supports high-purity material certification, environmental monitoring and geochemical research.

Future trends and potential applications

Further developments may include:

• Extension to additional analyte/matrix combinations
• Exploration of alternative reaction gases or mixed gas chemistries
• Integration of automated precursor-scan diagnostics
• Application in industrial QA/QC and regulatory testing

Conclusion

The Agilent 8800 ICP-QQQ operated in MS/MS mass-shift mode successfully eliminated hydride interferences on REEs, achieving ppt-level detection in complex matrices. This performance surpasses conventional ICP-QMS and supports accurate, high-sensitivity REE analysis.

Reference

1. Agilent 8800 Triple Quadrupole ICP-MS brochure, 5991-0079EN.
2. Sabine Becker and Hans-Joachim Dietze, Journal of Analytical Atomic Spectrometry, 1997, vol. 12, p. 881–889.
3. Naoki Sugiyama and Glenn Woods, Direct measurement of trace REEs in high-purity REE oxide using the Agilent 8800 ICP-QQQ with MS/MS mode, Agilent publication, 2012, 5991-0892EN.