Multi-Element Analysis of Petroleum Crude Oils using an Agilent 7900 ICP-MS

Significance of the topic

Elemental contaminants such as vanadium and nickel in crude oils can poison catalysts, damage equipment and affect product quality. With tightening industry limits on trace elements, high-sensitivity multi-element analysis is essential to support refining operations, ensure regulatory compliance, and facilitate trade via standardized methods.

Objectives and study overview

This work aimed to develop and validate a reliable, high-throughput procedure for multi-element determination in a range of crude oil types using an Agilent 7900 ICP-MS. Eighteen crude oil samples, spanning light to heavy grades, were analyzed to demonstrate method performance in terms of sensitivity, accuracy and reproducibility across common petroleum elements.

Methodology and instrumentation

Sample preparation involved simple dilution of approximately 1 g oil in o-xylene diluent with matrix modifiers and internal standards Sc and Y at 0.1 mg/kg. Dilution ratios ranged from 1:10 to 1:600 depending on sample concentration. Samples were shaken for 30 min and the introduction system rinsed between runs.

• Instrument Agilent 7900 ICP-MS with ASX-520 autosampler
• Nebulizer MicroMist concentric glass, solvent-resistant tubing
• Spray chamber Peltier-cooled quartz at −2 °C
• Interface Pt cones and organics drain kit to withstand O2-rich plasma
• Collision/reaction cell ORS4 with He mode for most interferences and optional H2 mode for reactive overlaps
• Oxygen additive (20 % in Ar) to decompose carbon matrix and prevent deposition on cones
• Operating settings RF power 1550 W, carrier gas 0.45 L/min, make-up gas 0.1 L/min, cell gas flows He 3.4 mL/min, H2 5 mL/min

Calibration employed oil-based multi-element standards from Conostan at 1–1000 µg/kg, with diluent as blank. A NIST SRM 1634c fuel oil reference was used to validate certified elements Ni and V and reference elements As and Se.

Main results and discussion

Calibration curves for all analytes were linear (R² > 0.998). Detection limits were in the low µg/kg range for most elements and background equivalents remained low despite organic matrix. Recoveries for V and Ni in NIST 1634c were within 10 % of certified values across multiple days. Isotopic confirmation of Ni using 60Ni and 62Ni showed excellent agreement. Quality control charts for As and Se over 12 months (147 measurements) demonstrated stable reproducibility and recoveries within +10 %.

Quantitative analysis of 18 crude oils revealed wide concentration ranges for key elements:

• Vanadium 0.07–301 mg/kg
• Nickel 0.21–67.8 mg/kg
• Iron 0.26–8.4 mg/kg
• Calcium

Benefits and practical applications

• Significantly lower detection limits and simple organic dilution enable rapid analysis
• Robust plasma and fast gas switching deliver reliable results in high-throughput labs
• Wide linear dynamic range supports both trace and major element quantification
• Compatibility with upcoming ASTM ICP-MS methods for petroleum strengthens standard-based testing

Future trends and potential applications

• Expansion of standardized ICP-MS methods to additional elements and matrices
• Integration with speciation techniques to understand element chemical forms
• Automation and online dilution systems for increased throughput
• Use of alternative organics and green solvents for improved safety and sustainability

Conclusion

The Agilent 7900 ICP-MS with ORS4 collision/reaction cell offers a robust, sensitive and accurate solution for multi-element analysis of crude oils following simple dilution in o-xylene. Method validation against NIST SRM confirmed excellent accuracy and reproducibility, making this approach well-suited for routine use in petroleum refining laboratories and compliant with evolving ASTM standards.

Reference

• ASTM International