Quantitation of Mercury in Petroleum by ETV-ICP-MS

Abstract

A technique for quantitating soluble and suspended mercurials in petroleum was evaluated as potentially useful for the analysis and screening of crudes and napthas. Crudes and napthas can contain hazardous concentrations of mercury capable of causing the embrittlement of aluminum piping and heat exchange equipment. Electro-Thermal Vaporization (ETV) was used to atomize the sample at 2650°C. The aerosol of this untreated sample was channeled via an argon gas stream into an Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). The study centers on the alkanes ranging from pentane (C₅) to dotriacontane (C₃₂) and reveals trends relevant to the analysis of mixed nonpolar unknowns. The system produces useful sensitivities in the range of C₅ to C₁₄ with a detection limit of 3 (±50%) parts per billion in pentane. For carbon mixtures above C₁₄ there was advanced equipment wear and suppression of the analytical signal. This suppression is attributed to changes in the sample transport efficiency and destabilization of the plasma due to a greater energy release for the longer chains. The formation efficiencies of the monovalent ion were considered, and several compounds were investigated. No statistical difference between the burning of diethyldithiocarbamate mercury (DEDTC Hg as found in Conostan standards) and elemental mercury as standards was found.