Online mercury speciation through liquid chromatography with particle beam/electron ionization mass spectrometry detection

Abstract

The ability of particle beam/electron ionization-mass spectrometry (PB/EI-MS) to provide elemental and molecular information for a sample solution has been evaluated for the speciation of inorganic and organic mercury compounds. Specifically, the EI process yields mass spectra which reflect the chemical species eluting from the chromatographic column, either atomic or molecular. A detailed evaluation of source temperature and electron energy parameters has been performed for the PB/EI-MS method. Preliminary studies demonstrated that the approach can be utilized for the determination of mercury at μg mL⁻¹ levels. A non-linear response at low concentrations (0.1–1 μg mL⁻¹) of mercury was observed due to poor transport of small particles through the PB interface. The use of KCl as a carrier agent to enhance particle transport was investigated. The analyte responses for mercury species showed higher sensitivity with good linearity upon KCl addition, providing limits of detection on the ng mL⁻¹ level (sub-ng absolute). The three mercury species (inorganic, phenyl- and methylmercury) were separated using a reversed phase (C₁₈) column with a total elution time of less than 11 min and the species were detected using PB/EI-MS. Post-column addition of the KCl carrier to the mobile phase was accomplished with a HPLC pump and a tee connection. It is believed that the PB/EI-MS technique is well suited not only for speciation of mercury, but also for obtaining comprehensive speciation information via atomic and molecular mass spectral information of diverse species, and thus can be used to solve a number of speciation challenges.