Analysis of trace elements in naphtha using the Thermo Scientific iCAP 7000 Plus Series ICP-OES

Significance of the Topic

Monitoring trace elements in naphtha is vital to avoid catalyst poisoning in petrochemical processes. Arsenic and other contaminants at single-digit µg/kg levels can inhibit catalytic activity and cause equipment fouling during steam cracking and reforming.

Objectives and Overview of the Study

This application note aims to demonstrate a straightforward workflow for direct analysis of volatile organic solvents using ICP-OES. The study evaluates the Thermo Scientific iCAP 7400 Plus Series ICP-OES equipped with a Peltier cooled spray chamber (GE IsoMist) to reduce naphtha volatility, ensuring stable plasma conditions and accurate quantification of a broad panel of elements.

Methodology and Instrumentation

Cooled the spray chamber to ‑10 °C to lower vapor pressure and limit plasma loading. Calibrated the ICP-OES with multi-element oil-based standards diluted in naphtha, covering Ag, Al, As, B, Ba, Ca, Cd, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Na, Ni, P, Pb, Si, Sn, Ti, V, and Zn. Employed radial viewing mode to minimize carbon emission interferences and optimized auxiliary and nebulizer gas flows for stable sampling. Wavelengths and background correction points were selected using Qtegra ISDS software.

Used Instrumentation

• Thermo Scientific iCAP 7400 Plus Series ICP-OES (Radial configuration)
• GE IsoMist Peltier cooled spray chamber set at ‑10 °C
• Glass concentric nebulizer

Main Results and Discussion

Method recovery for all spiked elements fell within ±5% of the target concentration. Relative standard deviations of triplicate measurements were typically below 0.5%, with a maximum of 1.36% for Ag. Method detection limits ranged from 0.04 µg/kg (Mg) to 13 µg/kg (B), demonstrating sub-single-digit µg/kg capability for most analytes. Radial viewing height and gas flow optimization suppressed carbon-based background and maintained plasma robustness during organic solvent introduction.

Benefits and Practical Applications of the Method

• Enables direct analysis of volatile matrices without dilution with heavier solvents
• Maintains plasma stability with reduced background and spectral interferences
• Achieves low µg/kg detection limits for a broad suite of elements
• Supports quality control and catalyst protection in petrochemical manufacturing

Future Trends and Potentials

Advances may include automated temperature control of spray chambers for diverse solvent systems, integration of process-line sampling interfaces for real-time monitoring, and application of high-resolution detectors to further reduce interferences. Expansion to other volatile organic mixtures in pharmaceutical and environmental analysis is anticipated.

Conclusion

Cooled spray chamber technology coupled with radial ICP-OES provides a robust, sensitive, and direct approach for trace element analysis in naphtha. The workflow delivers excellent precision and low detection limits, facilitating reliable monitoring of contaminants that impact catalyst life and process efficiency.