High-throughput High-precision Nd Isotope Ratios drom Small Samples Using Syringe Based Flow Injection for MC-ICP-MS

Importance of the Topic

High-precision 143Nd/144Nd isotope measurements are essential for tracking ocean circulation, provenance studies, and environmental monitoring. The inherently low Nd concentration in natural waters and the large number of samples required call for an analytical approach that combines minimal sample consumption with high throughput and reproducibility.

Aims and Overview of the Study

This study evaluates the performance of a Thermo Scientific NEPTUNE Plus MC-ICP-MS coupled with an Elemental Scientific microFAST MC apex Ω sample-introduction system. The goal is to determine 143Nd/144Nd ratios from small Nd aliquots (0.5–16 ng) with rapid turnaround and high precision.

Methodology and Instrumentation

Samples (La Jolla and JNdi reference materials) were treated as unknowns and measured versus an in-house Certipur® Nd standard, diluted in high-purity HNO₃. A dual-loop, syringe-driven microFAST MC injection setup alternately loads and rinses sample loops, delivering a steady-state flow to a PFA nebulizer at rates from 50 to 250 µl/min. The apex Ω desolvator integrates heating, condensation, and membrane drying under software control. The NEPTUNE Plus MC-ICP-MS equipped with a Jet interface and H-type skimmer cone provides high sensitivity and low oxide formation. Mass bias correction is applied linearly based on the 146Nd/144Nd ratio.

Main Results and Discussion

Under optimized conditions, the system measured sixteen 2 ng Nd samples per hour with an external reproducibility of 0.5 ε-unit (2σ). Sensitivity scaled linearly with injection rate up to 250 µl/min, and Nd oxide levels remained below 0.1%. For 16 ng sample loads, a precision of 0.13 ε-unit (2σ) was achieved. Measurements at lower sample amounts (down to 0.5 ng) maintained comparable repeatability across various injection rates and acquisition times, confirming method robustness for small-volume analyses.

Benefits and Practical Applications

• High throughput: 16 analyses per hour accelerate data acquisition for large sample sets.
• Minimal sample consumption: reliable isotope ratios from sub-nanogram Nd amounts enable studies of scarce or precious materials.
• Rapid washout and stable signals reduce carry-over and improve data quality.
• Software-controlled injection rates and desolvation parameters simplify method development and remote operation.

Future Trends and Potential Applications

Expansion of this approach to other isotopic systems (e.g., Sr, Hf); integration with automated separation modules for complex matrices; development of field-deployable micro-introduction platforms; implementation of machine-learning algorithms for real-time tuning and data validation to further enhance throughput and reliability.

Conclusion

The combination of the microFAST MC apex Ω and NEPTUNE Plus MC-ICP-MS delivers precise and accurate 143Nd/144Nd isotope ratios from sub-nanogram to tens of nanogram samples at high sample throughput. This platform meets the stringent requirements of modern geochemical, environmental, and QA/QC applications.