Determination of mercury species by capillary zone electrophoresis-inductively coupled plasma mass spectrometry: a comparison of two spray chamber–nebulizer combinations

Abstract

A method based on capillary zone electrophoresis (CZE) separation and inductively coupled plasma mass spectrometry (ICP-MS) detection is presented for the determination of methylmercury and inorganic mercury. The CZE conditions were optimised with respect to the flow rates for nebulizer gas and sheath solution, concentration of electrolyte and applied voltage. The performances of two different sample injection systems were compared. A standard cross-flow nebulizer with a Scott spray chamber offered a shorter analysis time, better resolution and ruggedness, while a micro-concentric nebulizer (MCN-100) with a cyclone spray chamber improved the detection limit by a factor of 11 for CH₃Hg⁺ and a factor of 19 for Hg²⁺. With the MCN-100, the detection limits were 13.6 ng ml⁻¹ for CH₃Hg⁺ and 6.0 ng ml⁻¹ for Hg²⁺, corresponding to absolute detection limits of 2.3 pg and 1.0 pg, respectively, for a hydrodynamic injection of 170 nl. The method was tested using three biological certified reference materials with a certified methylmercury content. The pre-treatment of biological samples involves only digestion and pH adjustment, without the need for derivatization or extraction, so that potential errors involved in these usually time-consuming steps can be avoided.