Direct multi-elemental analysis of crude oils using the Agilent 4200/4210 Microwave Plasma-Atomic Emission Spectrometer

Importance of the Topic

The determination of metal elements in crude oil is essential for reservoir management, catalyst performance, product quality and environmental compliance during facility decommissioning.

Study Objectives and Overview

This study evaluates a direct multi-element analysis of vanadium, calcium, iron, nickel, sodium and potassium in 20 crude oil samples using the Agilent 4200/4210 Microwave Plasma-Atomic Emission Spectrometer (MP-AES). A simple 1:10 dilution in o-xylene serves as sample preparation and results are compared with conventional ICP-OES and ICP-MS methods.

Methodology and Instrumentation Used

• Instrument: Agilent 4200 MP-AES with 4107 Nitrogen Generator, MicroMist nebulizer, double-pass glass cyclonic spray chamber, solvent-resistant tubing and External Gas Control Module (EGCM).
• Operating Conditions: EGCM set to low, pump rate 5 RPM, read time 3 s, three replicates, sample uptake delay 55 s, stabilization delay 10 s, fast pump during uptake and automatic background correction.
• Analyte Parameters: Calcium 396.847 nm, Iron 259.940 nm, Potassium 769.897 nm, Sodium 588.995 nm, Nickel 341.476 nm, Vanadium 311.070 nm and Scandium internal standard at 335.372 nm; all at 0.7 L/min nebulizer flow.
• Sample Preparation: Crude oils diluted 1:10 in o-xylene; mineral oil modifier, Chevron dispersant and scandium internal standard added to 10% oil (w/w).
• Calibration: Standards at 0, 2, 5 and 10 ppm; correlation coefficients ≥0.999; calibration fits linear or rational.
• Detection Limits: Method detection limits ranged from 0.008 ppm (Ni) to 0.190 ppm (K).
• Quality Control: Continuing calibration verification, high-level spikes (885 ppm) and analysis of NIST 1634c CRM yielded recoveries within ±10%.

Main Results and Discussion

Calibration curves exhibited excellent linearity across the 0-10 ppm range with R2 values ≥0.999. Detection limits were sufficient for trace analysis of crude oils. Spike recoveries in real samples were within ±10% of target values. Analysis of 20 crude oils revealed variable elemental concentrations depending on API gravity and composition. MP-AES results correlated closely with ICP-OES/ICP-MS data, demonstrating the method’s accuracy and reliability.

Benefits and Practical Applications

The MP-AES approach reduces sample preparation time, minimizes contamination risks and lowers operating costs by eliminating flammable gases such as acetylene and argon. Its robust nitrogen-based plasma enables unattended, safe operation, making it suitable for routine petrochemical laboratories and remote field settings.

Future Trends and Applications

Future developments may focus on portable MP-AES systems for on-site analysis, enhanced automation and software features for faster method setup, and expansion to other complex matrices such as refined fuels, bitumen and environmental samples.

Conclusion

The Agilent 4200/4210 MP-AES with EGCM provides a reliable, cost-effective and safe alternative for multi-element analysis of crude oils. By coupling simple dilution with advanced software and nitrogen plasma, this method delivers accurate results with reduced resource requirements and strong agreement with established ICP techniques.

References

• Nelson J, Gilleland G, Poirier L, Leong D, Hajdu P, Lopez-Linares F. Elemental Analysis of Crude Oils Using Microwave Plasma Atomic Emission Spectroscopy. Energy & Fuels. 2015;29(9):5587-5594.