Speciation of Mercury in Terrestrial Plants Using Vapor Generation and Liquid Chromatography–Inductively Coupled Plasma Mass Spectrometry

Abstract

A sensitive method for mercury speciation in biological samples is reported. A simple vapor generation apparatus was coupled to liquid chromatography and inductively coupled plasma–mass spectrometry (ICP–MS) to achieve a substantial increase in sensitivity. Mercury(II) and methylmercury were separated by reversed-phase chromatography as thiolate compounds with 2-mercaptoethanol. A short reverse phase column with an octylated stationary phase (75 × 4 millimeters) was used with a mobile phase containing 0.02 mole per liter ammonium acetate, 0.2 percent (v/v) 2-mercaptoethanol, and 1 percent methanol. The effluent was mixed with hydrochloric acid (0.06 mole per liter) containing platinum (40 micrograms per liter) as the internal standard and bismuth (30 micrograms per liter) as a modifying agent followed by sodium borohydride (0.016 mole per liter). The generated volatile species were introduced into the ICP–MS by conventional solution nebulization. In addition to the sensitivity enhancement induced by vapor generation, the addition of bismuth further increased the methylmercury signal with a reduced increase in the mercury(II) signal. As a result, comparable but unequal signals were achieved: the mercury(II) signal was approximately 1.6-fold higher than the methylmercury signal. Extraction with a hydrochloric acid-2-mercaptoethanol solution was used for sample preparation. The accuracy of determination was verified using two standard reference materials and an interlaboratory reference material based on barley grown hydroponically in mercury-contaminated solution. The method was employed for mercury speciation of plant samples from a polluted region.