Determination of P, Si and S in acid digested lubricating oil using the Agilent 8800 Triple Quadrupole ICP-MS

Significance of the Topic

The accurate quantification of silicon, phosphorus and sulfur in lubricating oils is essential for monitoring additive performance and identifying contaminants that impact engine efficiency and emissions.
Trace-level determination of these elements is challenging due to spectral interferences in traditional ICP-MS analyses.

Objectives and Study Overview

This study evaluates an optimized oxygen mass-shift method using the Agilent 8800 Triple Quadrupole ICP-MS for low-level determination of Si, P and S in lubricating oil.
The goals include assessing detection limits, accuracy and applicability to a NIST standard reference material.

Methodology and Instrumentation

Microwave-assisted acid digestion was performed on NIST SRM 1848 lubricating oil using sub-boiled HNO3 and H2O2.
The Agilent 8800 ICP-QQQ was operated in MS/MS mode with O2 as reaction gas at 0.5 mL/min.
Q1 was set to analyte masses and Q2 to oxide product masses: 28Si to 28Si16O, 31P to 31P16O and 32/34S to 32/34S16O.
Calibration standards ranged from 0.5 to 500 ppb in 1% HNO3.

Main Results and Discussion

Limits of detection were 0.25 ppb for Si, 0.01 ppb for P, and 0.18/0.75 ppb for 32S/34S oxides.
Calibration curves exhibited excellent linearity across the concentration range.
Recoveries in NIST 1848 digests ranged from 96.4 to 103%, demonstrating accurate interference removal and quantification.

Benefits and Practical Applications

The MS/MS mass-shift approach effectively eliminates common polyatomic interferences from N2 and CO species.
Sub-ppb detection enables trace monitoring of key elements in complex oil matrices for quality control and research.

Future Trends and Applications

Advances in triple quadrupole ICP-MS and reaction cell chemistries may enable broader multi-element analysis in hydrocarbon matrices.
Integration with isotope dilution and high-throughput workflows could enhance accuracy and speed for industrial QA/QC.

Conclusion

The Agilent 8800 ICP-QQQ with O2 mass-shift mode provides a robust, sensitive and accurate method for determining Si, P and S in lubricating oils.
The approach offers low detection limits and high recoveries, validating its suitability for challenging matrices.

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