Determination of Additive and Trace Elements in Lubricating Oil Using ICP-MS

Significance of the Topic

Monitoring both additive and trace elements in lubricating oil is essential for maintaining engine performance, preventing wear, and ensuring reliable equipment operation. Additive elements enhance lubricant properties, while trace metals derived from wear or contamination serve as early indicators of mechanical degradation. Accurate, sensitive analysis supports quality control, maintenance planning, and compliance with industry standards.

Objectives and Study Overview

This study evaluates the use of an ICPMS-2050 equipped with an organic solvent injection system to quantify additive and trace elements in automotive engine oil. Key aims include demonstrating simple sample preparation via organic solvent dilution, achieving low detection limits for a broad range of elements, and confirming accuracy through spike recovery experiments.

Instrumentation

The analytical setup comprises the following components and conditions:

• ICP-MS 2050 with Organic Solvent Torch and platinum sampling cone to resist solvent corrosion
• AS-20 autosampler featuring an organic solvent rinse station
• Solvent-resistant peristaltic pump tubing enabling in-line addition of internal standards
• Sample introduction via Nebulizer DC04 and Cyclone Chamber
• Ar–O2 mixed gas (70% Ar, 30% O2) in the interface to prevent carbon buildup
• Cell gas modes (No Gas, He, H2-A, H2-B) tailored per element
• Optimized gas flows: plasma Ar 20.0 L/min, auxiliary 0.50 L/min, carrier 0.40 L/min, dilution 0.20 L/min
• RF power 1.60 kW and chamber temperature at –5 °C

Methodology

Sample and standard preparation:

• Trace element analysis: 50-fold dilution (w/w) with organic solvent (PremiSolv)
• Additive element analysis: 5 000-fold dilution (w/w) with PremiSolv
• Calibration standards prepared from multi-element (S-21) and single-element solutions, spanning 0–200 µg/kg for trace elements and up to 100 000 µg/kg for sulfur
• Internal standard solution containing Be, Sc, Y, In, Bi mixed in oil-based solvent (sample:internal ratio ~4:1)
• Quantification by external calibration, applying dilution factors (trace elements 49.89×, additives 4 960×)

Key Results and Discussion

The instrument detection limits ranged from 0.03 to 1 000 µg/kg depending on element and cell mode. Spike recoveries for 18 trace elements and P, S fell between 88% and 116%, indicating minimal matrix interference and high accuracy. Elements such as Li, Na, Al, Si, P, S, and transition metals were quantified at low µg/kg levels. The method avoided complex acid digestion, thus reducing risks of volatilization or contamination.

Benefits and Practical Applications

• Simple and rapid sample preparation through direct organic solvent dilution
• High sensitivity and low detection limits for both additives and wear metals
• Reduced risk of sample contamination and analyte loss compared to acid digestion
• In-line addition of internal standards ensures consistent correction for signal drift
• Applicable to quality control, engine condition monitoring, and lubricant formulation studies

Future Trends and Potential Applications

Advancements may include automation of sample dilution and standard addition, real-time monitoring of lubricants in service, and extension to other complex organic matrices such as hydraulic fluids or gear oils. Coupling with speciation techniques could provide deeper insights into additive degradation pathways and corrosion processes.

Conclusion

The ICPMS-2050 with an organic solvent injection system provides a robust, accurate, and efficient approach for simultaneous determination of additive and trace elements in lubricating oil. The streamlined sample preparation and strong spike recoveries confirm its suitability for routine quality control and engine health monitoring in industrial and research laboratories.

References

1. ASTM D4951-14 Standard Test Method for Determination of Additive Elements in Lubricating Oils by Inductively Coupled Plasma Atomic Emission Spectrometry
2. ASTM D5185-18 Standard Test Method for Multielement Determination of Used and Unused Lubricating Oils and Base Oils by Inductively Coupled Plasma Atomic Emission Spectrometry