Rapid and robust determination of silicon in gasoline using the Thermo Scientific iCAP PRO XP ICP-OES Radial system

Significance of the Topic

The contamination of gasoline by silicon, even at trace levels, can lead to silica deposits that damage oxygen sensors and catalytic converters in vehicles. This not only affects engine efficiency and emission control systems but also incurs high maintenance costs. Rapid, precise determination of silicon content is essential for petrochemical producers and laboratories to ensure fuel quality and compliance with regulatory standards.

Objectives and Study Overview

This study aimed to develop and validate a fast, robust analytical method for measuring silicon in gasoline using the Thermo Scientific iCAP PRO XP ICP-OES Radial system. The protocol follows the Chinese standard GB/T 33647-2017 for silicon determination in motor gasoline, targeting a method detection limit below 20 µg/kg with minimal sample preparation.

Methodology

Gasoline samples were weighed (2.0 g) and diluted 1:4 (w/w) with isooctane. Calibration standards ranging from 0.1 to 2.0 mg/kg were prepared by diluting a 900 mg/kg silicon-in-oil standard in isooctane. A Thermo Scientific Qtegra ISDS LabBook managed all analytical parameters, including selection of the Si 251.611 nm emission line, an exposure time of 10 s, and optimized gas flows for plasma stability. Oxygen was added to the plasma via an auxiliary mass flow controller to minimize carbon-based spectral interferences and torch fouling.

Instrumentation Used

• Thermo Scientific iCAP PRO XP ICP-OES Radial with vertical torch geometry
• Ceramic D-Torch (SiAlON) for enhanced resistance to organic matrices
• IsoMist cooled spray chamber (–15 °C)
• Concentric glass nebulizer and peristaltic pump (20 rpm)
• Additional oxygen flow (40 mL/min) to reduce carbon deposits

Key Results and Discussion

Linearity was demonstrated over 0.1–2.0 mg/kg with R² = 0.9999 and relative standard error of 4.3%. The instrument detection limit was 0.004 mg/kg, the method detection limit (MDL) 0.020 mg/kg, and the method quantification limit (MQL) 0.067 mg/kg. Spike recoveries in different gasoline grades (92#, 95#, 98#) ranged from 90.1% to 95.3%. Repeatability tests on a 0.230 mg/kg silicon blank showed RSD <1.5% over seven replicates, confirming excellent precision and accuracy.

Benefits and Practical Applications

• Rapid analysis: <1 min per sample, enabling high throughput
• Minimal sample preparation: direct dilution and injection avoids digestion
• Robust performance: ceramic torch and oxygen addition reduce maintenance
• Compliance: meets GB/T 33647-2017 requirements for motor gasoline analysis

Future Trends and Potential Applications

Advances may include automated sample handling and integration with on-line monitoring systems for real-time quality control. Expansion of the method to other trace elements could broaden its use in refining and petrochemical industries. Further developments in plasma chemistry and spectrometer sensitivity will enhance interference removal and lower detection limits.

Conclusion

The Thermo Scientific iCAP PRO XP ICP-OES Radial system, combined with a simple isooctane dilution and oxygen addition, provides a rapid, accurate, and robust method for silicon determination in gasoline. This protocol ensures compliance with national standards and supports efficient, high-throughput analysis in petrochemical quality control laboratories.

References

GB/T 33647-2017: Determination of silicon content in motor gasoline by ICP-OES