Specification Analysis of Gasoline by HR ICP-OES Application Note · PlasmaQuant 9100 Elite

Introduction

Volatile Organic Compounds (VOC) such as gasoline and naphtha are subject to specification analysis in terms of trace elemental analysis of environmental pollutants (e.g. lead) and compounds that are potentially harmful to engines and turbines. Elements such as vanadium, iron, nickel, or silicon contribute to corrosion processes and therefore bear the risk of engine or sensor failure in automobiles or aircrafts. Due to the potential environmental hazard and risk of technical breakdown caused by trace elemental impurities, their analysis is subject of many regulations, such as ASTM D5708, ASTMD7111, UOP389, and DIN EN 228, requesting maximum levels in the ppb range for elements such as Al, As, Fe, K, Na, Ni, P, Pb, Si and V. The value of petroleum is often defined by the specification of such elements.

VOC are among the most challenging samples to be analyzed by ICP techniques. For specification analysis in the low μg/kg range, ICP-MS is often the method of choice as conventional ICP-OES instruments lack sensitivity due to the necessity of sample dilution and the occurence of spectral interferences. Typical analytical challenges are the poor short-term and long-term stability due to the high volatility of the samples and to the high risk of soot formation caused by the high carbon content of the samples. Furthermore, the carbon-based emission complicates the spectra as-recorded and bears the risk of severe spectral interferences. Conventional ICP-OES instrumentation is forced to use less sensitive lines for many analytes, since interferences on primary lines cannot be resolved properly.

Due to the vertical plasma geometry of the V Shuttle Torch and the unique plasma performance of its High-Frequency Generator, direct analysis of undiluted gasoline proved feasible for the analytical routine on the PlasmaQuant 9100 Elite. By avoiding soot formation and memory effects, frequent torch replacement becomes a relic of the past and detection limits below 1 μg/kg for iron, nickel, and vanadium push the boundaries of ICP-OES detectability. Hence, the PlasmaQuant 9100 Elite represents a suitable alternative to ICP-MS instrumentation for the analysis of VOC.

Carbon-based spectral interferences are successfully removed by the high spectral resolution of the High-Resolution Optics. Excellent method robustness was confirmed by a continuous aspiration test, which showed minor intensity drifting of all emission lines during 3.5 hours of uninterrupted submission of undiluted gasoline.