Accurate analysis of neptunium 237 in a uranium matrix, using ICP-QQQ with MS/MS

Significance of the topic

Neptunium 237 is a long-lived radioactive actinide produced in nuclear reactors and present in environmental and waste materials. Its high aqueous mobility, affinity for calcium-rich substrates, and half-life of 2.14 million years demand reliable ultra-trace monitoring to ensure environmental safety, effective waste management, and radiation protection.

Study objectives and overview

This application note assesses the capability of triple quadrupole inductively coupled plasma mass spectrometry with MS MS (ICP QQQ) to resolve neptunium 237 from interferences arising from uranium 238 in complex matrices. The performance of ICP QQQ is compared to conventional single quadrupole ICP MS in terms of abundance sensitivity and quantitative accuracy.

Instrumentation Used

The analysis employed an Agilent 8800 ICP QQQ system fitted with an SPS 4 autosampler. Sample introduction used a Micromist nebulizer, quartz spray chamber, quartz torch, and nickel interface cones. Key operating settings included RF power at 1550 W, nebulizer gas flow of 1.15 L per minute, spray chamber temperature of 2 degrees Celsius, and a sampling depth of 8.0 mm. MS MS mode utilized unit mass filtering in both quadrupoles to deliver overall abundance sensitivity below 1 times 10 to the minus 10.

Methodology

Uranium matrix solutions were prepared at concentrations of 1, 10 and 100 milligrams per liter. Each level was measured unspiked and spiked with neptunium at 0.1 and 1.0 micrograms per liter. Calibration standards ranged from 100 to 2000 nanograms per liter prepared in 2 percent nitric acid. Analyses were conducted in single quadrupole mode and MS MS mode to evaluate the impact of improved abundance sensitivity on interference removal.

Key results and discussion

• MS MS mode fully eliminated tailing from the intense uranium 238 peak, enabling clear detection of 100 parts per trillion neptunium 237 in a 10 parts per million uranium matrix. Single quadrupole mode exhibited significant overlap.
• Calibration curves showed perfect linearity over the 100 to 2000 parts per trillion range with coefficient of determination of 1.0000. Background equivalent concentration was 0.0009 nanograms per liter and detection limit was 0.0031 nanograms per liter.
• In uranium matrices up to 100 milligrams per liter, ICP QQQ achieved accurate recoveries of neptunium spikes at 0.1 and 1.0 micrograms per liter, even at million to one uranium to neptunium ratios. Conventional ICP MS produced false positive signals that increased with uranium concentration due to poorer abundance sensitivity.

Benefits and practical applications of the method

• Unmatched resolution of neptunium 237 from uranium interferences supports reliable ultra-trace quantification in environmental, nuclear fuel, and waste samples.
• High sensitivity and exceptionally low background enable monitoring at regulatory compliance levels.
• The robust MS MS configuration enhances routine quality assurance and control workflows in analytical laboratories handling actinides.

Future trends and potential applications

Further improvements in multi quadrupole ICP MS are expected to reduce detection limits and simplify interference removal. Integration with automated sample preparation and chromatographic separation may extend applications to biological assays. Development of optimized reaction gas chemistries could address emerging challenges in nuclear forensics and advanced actinide research.

Conclusion

ICP QQQ with MS MS offers superior abundance sensitivity compared to single quadrupole ICP MS, effectively resolving uranium tailing and enabling precise ultra-trace analysis of neptunium 237. This approach provides a reliable solution for environmental monitoring and nuclear material characterization, overcoming the interference limitations of traditional systems.

References

• The NUBASE Evaluation of Nuclear and Decay Properties. Nuclear Physics A 729:3–128. DOI 10.1016/j.nuclphysa.2003.11.001