Trace level analysis of sulfur, phosphorus, silicon and chlorine in NMP using the Agilent 8800 Triple Quadrupole ICP-MS

Significance of the Topic

The analysis of trace levels of sulfur, phosphorus, silicon and chlorine in N-Methyl-2-pyrrolidone (NMP) is critical for semiconductor manufacturing, where any residual non-metallic contaminant can degrade wafer performance. Conventional ICP-MS struggles with low ionization efficiencies and matrix-derived polyatomic interferences, making reliable detection at sub-ppb levels extremely challenging.

Objectives and Overview of the Study

This application note evaluates the performance of an Agilent 8800 Triple Quadrupole ICP-MS (ICP-QQQ) operated in MS/MS mode for the determination of S, P, Si and Cl in electronic-grade NMP. The goal is to achieve background equivalent concentrations (BECs) and detection limits suitable for semiconductor process control.

Instrumentation Used

• Agilent 8800 Triple Quadrupole ICP-MS with semiconductor configuration (Pt interface cones, high-transmission ion lens)
• Organics torch with 1.5 mm injector to reduce plasma loading
• C-flow 200 μL min⁻¹ PFA nebulizer in self-aspiration, carrier gas 0.50 L min⁻¹ Ar
• Optional 20 % O₂ in Ar added to carrier gas to limit carbon buildup

Methodology and Sample Preparation

Semiconductor-grade NMP was purified by sub-boiling distillation and acidified to 1 % w/w HNO₃. Analyses were performed directly by standard addition without further dilution. Key strategies included:

• Use of MS/MS mode: Q1 set to analyte or precursor mass, reaction cell gas (O₂ or H₂), Q2 monitoring product ions.
• O₂ mass-shift for P and S to form PO⁺ and SO⁺, avoiding N/O/C polyatomic interferences.
• H₂ on-mass for Si (SiH⁺ suppression of N₂⁺/CO⁺) and H₂ mass-shift for Cl to form H₂Cl⁺, enhancing selectivity.

Main Results and Discussion

MS/MS with mass-shift provided BECs and detection limits an order of magnitude lower than single-quad mode:

• Phosphorus (PO⁺, m/z 47): BEC 0.55 ppb, DL 0.06 ppb
• Sulfur (SO⁺, m/z 48): BEC 5.5 ppb, DL 0.25 ppb
• Silicon (SiO₂⁺, m/z 60): BEC 11.9 ppb, DL 0.48 ppb
• Chlorine (H₂Cl⁺, m/z 37): BEC 34.2 ppb, DL 3.6 ppb

O₂ cell gas delivered optimal mass-shift chemistry for P, S and Si, while H₂ was superior for Cl. MS/MS rejects matrix-derived interferences at Q1, enabling clean product-ion detection and linear calibration.

Benefits and Practical Applications of the Method

• Achieves semiconductor-grade detection criteria for non-metals in organic solvents.
• Single-vial analysis by automated MS/MS sequence reduces hands-on time.
• Flexibility to switch between on-mass and mass-shift approaches for different analytes.

Future Trends and Potential Applications

Advances in triple-quad ICP-MS allow exploration of new reaction gases and kinetic regimes to target increasingly complex matrices. Future work may integrate automated dilution, in-line reaction-gas blending and data analytics for real-time process monitoring across pharmaceutical, petrochemical and polymer industries.

Conclusion

The Agilent 8800 ICP-QQQ in MS/MS mode successfully overcomes the low ionization and severe polyatomic interferences inherent in NMP, delivering low-ppt detection capabilities for S, P, Si and Cl. This approach meets stringent semiconductor requirements and offers a robust, streamlined workflow for trace non-metal analysis.

References

1. Agilent Technologies. Understanding oxygen reaction mode in ICP-MS/MS. Agilent publication 5991-1708EN, 2013.
2. Ikezo Y., Matsuoka S., Takebe M., Viggiano A. Gas phase ion-molecule reaction rate constants through 1986. Maruzen Company Ltd., 1987.