Effect of plasma pressure on the determination of mercury by microwave-induced plasma atomic emission spectrometry

Abstract

The determination of very low levels of mercury was studied using microwave-induced plasmas (MIPs) sustained in a surfatron at reduced pressures, in the range 2–100 Torr, and at atmospheric pressure. An on-line continuous mercury cold vapour generation system was employed as the sample introduction method. Helium and argon were investigated comparatively as plasma gases. The optimization of the operating conditions, the analytical figures of merit for the determination of mercury by atomic emission spectrometry, and the effect of potential interferents such as carbon dioxide have been studied. Low pressure argon discharges proved to be superior, in terms of detection limits (DLs), to atmospheric pressure MIPs for the excitation of the atomic mercury: DLs (3s) of 0.7 pg ml^–1 for a 40 Torr argon discharge and of 8 pg ml^–1 at atmospheric pressure were obtained, while the DLs obtained using helium MIPs were 3 and 4 pg ml^–1, respectively. Moreover, the low pressure MIPs also showed a higher resilience to the introduction of foreign gases in the discharge. A method is proposed which has been successfully applied to the determination of Hg^II) using a 40 Torr argon MIP.