Determination of Trace Elements in a Xylene Solution of Oil By ICP-OES with Ultrasonic Nebulization and Membrane Desolvation

Importance of the topic

Trace element analysis in oil is critical for industrial quality control and environmental monitoring. Determining impurities at sub-ppb levels ensures equipment longevity, regulatory compliance and product performance.

Objectives and Study Overview

This study aimed to quantify 17 trace elements (Mo, Ag, Ti, Sn, Ba, B, Mn, Fe, Cr, Mg, V, Ca, Cu, Pb, Ni, Cd and Al) at a target concentration of 10 µg/kg in a xylene-diluted oil solution. Challenges such as plasma instability and carbon deposition were addressed by introducing oxygen into the auxiliary argon flow and by employing advanced sample introduction.

Methodology and Instrumentation Used

Oil samples and calibration standards (10–50 µg/kg) were prepared by diluting a 1 mg/kg stock in xylene. An Agilent Liberty 150 AX Turbo axial-view ICP-OES (1.7 kW, 40.68 MHz RF) was coupled to a Cetac U-6000 AT+ ultrasonic nebulizer with membrane desolvation. The SPS-5 auto-sampler and an AGM-1 oxygen accessory were used to introduce standards and maintain plasma stability.

• Power: 1.5 kW
• Plasma gas: 15.0 L/min Ar
• Auxiliary gas: 1.5 L/min Ar + 1.5 L/min O₂
• Ultrasonic nebulizer: 140 °C heating, 3 °C cooling
• Membrane desolvator: 160 °C heating, 1.2 L/min Ar
• Replicates: 3, background correction: dynamic

Main Results and Discussion

Calibration curves for all 17 elements showed correlation coefficients above 0.99. Signal precision for a 50 µg/kg standard was within 0.6–3.6 %RSD. Analysis of a 10 µg/kg sample yielded recoveries from 89 % to 107 %, demonstrating accurate quantification at trace levels despite the organic matrix.

Benefits and Practical Applications of the Method

The combination of ultrasonic nebulization and membrane desolvation reduces solvent load in the plasma and minimizes spectral interferences from hydrocarbons. Key advantages include:

• Rapid, reproducible trace analysis with minimal sample prep
• Stable plasma operation when handling organic solvents
• High throughput suitable for routine QC in oil refinery and petrochemical laboratories

Future Trends and Potential Applications

Advances may include integrated on-line monitoring of oil streams, further miniaturization of desolvation interfaces and coupling with high-resolution detectors for improved detection limits. The approach can extend to other organic matrices such as fuels, lubricants and bio-oils.

Conclusion

Axial ICP-OES with ultrasonic nebulization and membrane desolvation provides accurate, precise and efficient determination of trace metals in oil at 10 µg/kg levels. The method supports routine automated analysis without extensive sample preparation.

Reference

1. Johnson D. Determination of metals in oils by ICP-AES, ICP at work (ICP-13), Varian Analytical Instruments, 1993.
2. Cetac Technologies. U-6000AT+ Ultrasonic Nebulizer/Membrane Desolvator Operator’s Manual, 1995.
3. Nham T. Determination of lead in unleaded gasoline by ICP-AES with oxygen and cooled spray chamber, ICP at work (ICP-15), Varian Australia Pty Ltd, 1993.