Direct coupling of high-performance liquid chromatography to microwave-induced plasma atomic emission spectrometry via volatile-species generation and its application to mercury and arsenic speciation

Abstract

The on-line coupling of vesicle-mediated high-performance liquid chromatography (HPLC) to low-power argon microwave-induced plasma (MIP) detection is described. The analytical potential of such a hybrid technique is illustrated for the speciation of mercury and arsenic compounds. Continuous cold vapour (CV) or hydride generation (HG) techniques were used as interfaces between the exit of the HPLC column and the MIP, held in a surfatron at reduced pressure. Detection was by atomic emission spectrometry (AES). The effect of different surfactants on mercury CV generation was evaluated using SnCl₂ as the reducing solution instead of sodium tetrahydroborate(III). Emission signals increased by about 75% by adding the vesicle-forming surfactant didodecyldimethylammonium bromide (employed as the HPLC mobile phase for speciation). Enhancements of around 100% of signals were found in micelles of cetyltrimethylammmonium bromide. The detection limits by vesicular HPLC–HG-MIP-AES for the more toxic arsenic species investigated (namely, arseneous, arsenic, monomethylarsonic and dimethylarsinic acids) were in the range 1–6 ng ml^–1. The detection limits for mercury speciation by vesicular HPLC–CV-MIP-AES were 0.15 ng ml^–1 Hg for inorganic mercury and 0.35 ng ml^–1 Hg for methylmercury. Both methods have been successfully applied to the speciation of mercury and arsenic in natural waters (sea-water and tap water) and in human urine.