Robust and sensitive determination of multi-elements in N-methyl-2-pyrrolidone (NMP) using ICP-OES

Significance of the topic

N-Methyl-2-pyrrolidone (NMP) is widely used in lithium-ion battery manufacturing and recycling due to its high chemical and thermal stability and miscibility with both aqueous and organic phases. Monitoring trace elements in NMP is crucial for quality control, environmental safety, and process optimization. Inductively coupled plasma–optical emission spectroscopy (ICP-OES) offers multi-element detection, high sensitivity in the µg L⁻¹ range, and resilience against organic matrices, making it an ideal analytical technique for NMP.

Objectives and study overview

• Demonstrate the suitability of the Thermo Scientific iCAP PRO XP ICP-OES Duo equipped with the iSC-65 Autosampler for automated, robust analysis of trace metals in NMP.
• Validate method performance in terms of sensitivity, linearity, accuracy, precision, and long-term stability.
• Assess extraction of trace elements from real cathode materials exposed to NMP under different conditions.

Methodology and instrumentation used

• Instrumentation: Thermo Scientific iCAP PRO XP ICP-OES Duo, iSC-65 Autosampler, quartz torch, organic spray chamber, concentric nebulizer, auxiliary oxygen flow.
• Sample introduction: Self-aspiration with PFA capillary for undiluted NMP; peristaltic Tygon tubing for 10× diluted NMP.
• Calibration: Single-element standards in undiluted and 10× diluted NMP; Yttrium internal standard at 1000 µg L⁻¹.
• Measurement modes: Axial full range (iFR) and enhanced ultraviolet (eUV) to cover emission lines from 167.021 to 852.145 nm.
• Real sample test: Cathode material and aluminum substrate soaked in undiluted NMP for 1 hour and 24 hours.

Main results and discussion

• Peristaltic tubing compatibility: Tygon tubing resisted 10× diluted NMP without leaching; PVC and Viton released Zn, Ca, Mg, Na, K impurities.
• Calibration performance: Linear regression R² > 0.999 over 25–100 µg L⁻¹ (metals) and 100–10 000 µg L⁻¹ (non-metals).
• Detection limits: µg L⁻¹ range, with diluted NMP showing lower MDLs due to reduced carbon background.
• Spike recovery: 95–110 % with RSD < 3 % for all analytes in 10× diluted NMP.
• Long-term robustness: 236 sample analyses over 4.5 hours; CCV RSD < 1.5 % and internal standard recovery 94–103 %.
• Real sample extraction: Minimal leaching for intact cathodes; damaged surfaces released Li, Mn, Ni, S, and P, demonstrating matrix impact.

Benefits and practical applications of the method

• Fully automated workflow reduces manual handling and contamination risk.
• High sensitivity for UV-emitting elements (S, P, Cd, Pb) with extended UV mode.
• Robust performance over extended sequences supports high-throughput QC and production labs.
• Applicable to battery manufacturing, recycling, and other industries requiring organic solvent analysis.

Future trends and potential applications

• Development of greener solvents and integration of real-time monitoring for sustainable battery production.
• Advanced materials and microfluidic sample introduction for handling undiluted solvents automatically.
• AI-driven data analytics for predictive maintenance and method optimization.
• Extension of methodology to pharmaceutical, petrochemical, and other organic matrices.

Conclusion

The Thermo Scientific iCAP PRO XP ICP-OES Duo combined with the iSC-65 Autosampler enables sensitive, accurate, and robust multi-element analysis of NMP after minimal dilution. The validated method demonstrates low detection limits, excellent accuracy, and stability, providing a reliable solution for routine monitoring in battery manufacturing and recycling.

References

1. Liu et al. Current and future lithium-ion battery manufacturing, iScience 2021, 24, 103332.
2. Li et al. Water-based electrode manufacturing and direct recycling of lithium-ion battery electrodes—A green and sustainable manufacturing system; iScience 2020, 23, 101081.