NEPTUNE and NEPTUNE Plus: Breakthrough in Sensitivity using a Large Interface Pump and New Sample Cone

Importance of Topic

The development of high-sensitivity multicollector ICP-MS is critical for geochemical, environmental and nuclear isotope analysis. Enhanced ion transmission and reduced background improve detection limits, precision and accuracy for trace element and isotope ratio measurements across a broad mass range, enabling more reliable data in research and quality-control applications.

Objectives and Study Overview

The study evaluates two new hardware upgrades on the Thermo Scientific NEPTUNE™ platform: a large interface pump (100 m³/h) and a redesigned sample cone (“Jet” cone). Goals include:

• Quantifying sensitivity gains versus standard interface pump (30 m³/h).
• Assessing argon background and oxide formation impacts.
• Evaluating accuracy and precision for Sr, Nd, Hf and U isotope ratios.

Analytical Methodology

Low-resolution MC-ICP-MS analyses were performed using an Aridus II desolvating nebulizer with 100 µL/min uptake. An extended electronic baseline, defocused ion beam, daily gain cross-calibration and isobaric corrections (Sm, Rb, Kr, Yb, Lu) ensured robust performance. Sample bracketing and exponential mass bias correction were applied using certified reference ratios.

Used Instrumentation

• Thermo Scientific NEPTUNE Plus MC-ICP-MS (low resolution, 450).
• Aridus II desolvating nebulizer (PFA concentric, 100 µL/min).
• Large interface pump (100 m³/h) upgrade kit.
• Standard and X-skimmer cones, plus Jet sample cone.
• Thermo Tune Solution with Li, Fe, Nd, Hf, Tl, Sr, Pb, U standards.

Main Results and Discussion

Sensitivity Enhancement: Using the large interface pump and X-skimmer cone, signal improvements ranged from 50× for Li to 5× for U compared to the standard pump. Absolute sensitivities (V/ppm) reached 3200 (Li), 1600 (Fe), 1200 (Sr), 900 (Nd, Hf), 1100 (Pb, U).
Jet Cone Performance: The Jet sample cone further boosted sensitivity for heavy elements (Pb 2800 V/ppm; U 2500 V/ppm) and maintained lighter element responses.
Argon and Oxide Formation: Total Ar signal (~8000 V) and UO+/U+ ratio (~1 %) were unchanged by the large pump, indicating stable plasma conditions.
Precision and Accuracy: External reproducibilities (2σ) for 10 ppb solutions were 9 ppm (87Sr/86Sr), 8 ppm (143Nd/144Nd) and 13 ppm (176Hf/177Hf). U isotope ratios at 1 ppb showed <0.8 ‰ (234U/238U) and <0.2 ‰ (235U/238U) precision with negligible bias versus true values.

Benefits and Practical Applications

• Lower detection limits enable analysis of ultratrace and scarce samples.
• Improved precision and accuracy support high-confidence isotope geochemistry and nuclear forensics.
• Retrofit compatibility allows upgrades of existing NEPTUNE systems.

Future Trends and Opportunities

Continued optimization of sample cone geometries and interface pumping schemes may further enhance sensitivity for superheavy elements. Integration with automated sample introduction and matrix removal strategies will broaden application to challenging matrices in environmental monitoring, biogeochemistry and isotope forensics.

Conclusion

The large interface pump and Jet sample cone dramatically increase MC-ICP-MS sensitivity across the mass range without compromising background, oxide levels or mass bias. These upgrades enable high-precision Sr, Nd, Hf and U isotope analysis down to sub-ppb levels, supporting advanced geochemical and nuclear investigations.

References

1. Newman, K., Freedman, P.A., Williams, J., Belshaw, N.S. & Halliday, A.N. (2009) High sensitivity skimmers and non-linear mass dependent fractionation in ICP-MS. Journal of Analytical Atomic Spectrometry, 24, 742–751.