Determination of Lead in Unleaded Gasoline by ICP–OES with the Use of Oxygen and a Cooled Spray Chamber

Importance of the Topic

The trace determination of lead in unleaded gasoline remains critical due to its historical contribution to atmospheric pollution and human health risks. Although leaded additives have been phased out, residual organolead compounds in modern fuels require precise monitoring to ensure environmental compliance and public safety.

Study Objectives and Overview

This work presents an analytical procedure for quantifying lead in unleaded gasoline by inductively coupled plasma–optical emission spectrometry (ICP–OES). The method employs oxygen addition to the plasma and a cooled spray chamber to stabilize measurements. Accuracy and precision were evaluated using a National Institute of Standards and Technology (NIST) Standard Reference Material (SRM 2712).

Methodology and Instrumentation

Sample preparation converts alkyl lead species into iodo lead complexes stabilized by a quaternary ammonium reagent. Reagents and conditions include:

• Iodine for oxidation of organolead compounds
• Aliquat 336 in decahydronaphthalene for phase separation
• Iso-octane or decalin as solvent

The instrumentation setup comprises:

• Agilent Liberty 220 ICP–OES
• Cooled glass spray chamber at –10 °C (ethylene glycol coolant)
• Oxygen introduced into auxiliary Ar flow at 0.035 L/min
• Demountable torch with 0.8 mm i.d. injector tube
• Concentric glass nebulizer at 80 kPa, sample uptake 0.2 mL/min
• Detection at Pb 283.306 nm emission line

Main Results and Discussion

Key findings include:

• Oxygen addition prevents carbon buildup on torch components and maintains plasma stability.
• Cooled spray chamber reduces solvent vapor load, achieving 1% signal decay in 33 s and baseline recovery in 130 s.
• Standard addition calibration yields precision of 1–5% RSD; continuous measurement over one hour showed 0.7–1.1% RSD.
• Measured Pb in NIST SRM 2712 (0.0080 g/L) agrees with the certified value (0.0079 g/L).

Benefits and Practical Applications

The described ICP–OES approach offers a wide dynamic range, low chemical interferences, and the capability for multi-element analysis. It is well suited to routine quality control in petroleum laboratories, environmental monitoring, and regulatory compliance testing.

Future Trends and Opportunities

Potential developments include:

• Automation of sample handling and data analysis workflows
• Extension of the approach to biofuels and complex volatile matrices
• Advances in cooled nebulizer technology for further vapor suppression
• Coupling with mass spectrometry to enhance sensitivity and selectivity

Conclusion

The incorporation of oxygen into the plasma and the use of a cooled spray chamber enable reliable, sensitive, and stable determination of lead in unleaded gasoline. The method demonstrates excellent agreement with certified standards and robust performance over extended analysis periods.

Reference

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