Direct measurement of metallic impurities in petroleum fuels using the 4100 MP-AES

Importance of the topic

Engine and turbine components are sensitive to trace levels of metals such as calcium, magnesium, sodium and potassium in gasoline and diesel fuels. Monitoring these elements is crucial to prevent corrosion, deposit formation and performance degradation. Regulatory standards, for example ASTM D6751 and ASTM D2880, set limits on combined concentrations of alkaline earth and alkali metals to ensure fuel quality and equipment longevity.

Objectives and study overview

This study demonstrates a rapid, direct method for quantifying Mg, Ca, Na and K in gasoline without sample digestion or dilution. The approach leverages Agilent’s 4100 Microwave Plasma Atomic Emission Spectrometer (MP-AES) and an optimized workflow to achieve low detection limits, high accuracy and reduced operating costs compared with conventional techniques.

Methodology

• Direct analysis of gasoline samples using standard addition calibration to address matrix volatility and avoid dilution with kerosene.
• Method detection limit determination based on three times the standard deviation of multiple blank measurements.
• Spike recovery assessment at target concentrations to evaluate method accuracy within ±10 %.

Used instrumentation

• Agilent 4100 MP-AES with nitrogen plasma excitation to eliminate flammable gases and reduce costs.
• External Gas Control Module (EGCM) for controlled air injection to prevent carbon buildup and stabilize plasma.
• OneNeb inert nebulizer and double-pass glass cyclonic spray chamber for efficient aerosol generation at low flow rates.
• IsoMist cooled spray chamber to minimize solvent loading and maintain plasma stability with volatile samples.

Main results and discussion

• Detection limits in gasoline: Mg 2.7 ppb, Ca 4.3 ppb, Na 5.3 ppb, K 29.4 ppb, all well below target regulatory levels.
• Calibration linearity with correlation coefficients above 0.999 for all elements, supporting reliable quantification.
• Spike recoveries between 95 % and 100 % for Mg, Ca, Na and K at 1.1 ppm, demonstrating method accuracy in real matrices.

Benefits and practical applications

• Eliminates sample digestion and hazardous gas handling, streamlining routine fuel analysis in quality control laboratories.
• Reduces operating costs compared with flame atomic absorption by using inexpensive nitrogen plasma and no hollow cathode lamps.
• Enables unattended operation and faster throughput, improving laboratory efficiency.

Future trends and potential applications

• Integration of MP-AES with online monitoring systems for continuous fuel quality assessment in refineries and fuel distribution.
• Expansion to analysis of alternative and bio-derived fuels, leveraging robust plasma tolerance to complex matrices.
• Coupling with separation techniques or chemometric algorithms for multi-element profiling and predictive maintenance.

Conclusion

The Agilent 4100 MP-AES combined with EGCM, OneNeb nebulizer and IsoMist cooled chamber provides a robust, accurate and cost-effective solution for direct quantification of metallic impurities in gasoline. The method meets stringent detection and accuracy requirements while eliminating the need for flammable gases and extensive sample preparation, offering a practical approach for routine fuel quality monitoring.

Reference

1. ASTM International, ASTM D6751 – 11b, Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels, 2011.
2. ASTM International, ASTM D2880 – 03, Standard Specification for Gas Turbine Fuel Oils, 2003.
3. J. Moffett and G. Russell, Evaluation of a novel nebulizer using an inductively coupled plasma optical emission spectrometer, Agilent Application Note 5990-8340EN.