Applications of ultrasonic nebulization in the analysis of petroleum and petrochemicals by inductively coupled plasma atomic emission spectrometry

Abstract

The availability in recent years of stable, reliable ultrasonic nebulizers (USN) for inductively coupled plasma atomic emission spectrometry (ICP-AES) has led to new applications of ICP-AES in the petroleum and petrochemical industries. These applications take advantage of the high efficiency and high sensitivity of the USN and/or its desolvation capability and include: direct analysis of volatile hydrocarbons such as toluene, naphtha, isopropranol, etc., for trace elements; direct determination of lead in aviation fuel; trace analysis of solvents, distillate oils and low-ash polymers prepared by high temperature ashing; and rapid analysis of heavy oils and finished lubricating oils by microwave digestion of small (0.1 g) samples. This paper presents the status of development of each of the above applications contrasting the performance of the standard pneumatic-type nebulizer system (cross-flow) and the USN. The analysis of volatile hydrocarbons uses the desolvator to remove most of the organic vapour prior to introduction into the plasma. Although this may be accomplished using a cooled spray chamber attached to a pneumatic nebulizer, the high efficiency of the USN provides additional sensitivity tending to offset degradation in performance due to residual solvent loading and organic spectral background effects. The injection of oxygen into the outer and aerosol carrier streams further decreases these effects and yields detection limits for toluene and other solvents that are comparable with the aqueous performance of the USN.