Dielectric barrier discharge-assisted determination of methylmercury in particulate matter by atomic absorption spectrometry

Abstract

Particulate matter (PM) impregnated with methlymercury (MeHg⁺) was analyzed using atomic absorption spectrometry coupled to a customized dielectric barrier discharge (DBD) device. Chemical vapor generation (CVG) was applied to generate methylmercury hydride and the DBD device promoted bond cleavage with subsequent release of free Hg atoms to the gas phase. Hydride generation was carried out using a lab-made syringe-based device in batch mode using argon as a carrier gas. Optimized conditions included the use of 1.0 mL of a 0.05% m/v NaBH₄ solution and 1.0 mL of a 10% v/v HCl solution. This system was coupled to the DBD device, designed to operate in “plasma jet” configuration. Assessment of the designed device for methylmercury detection was established based on an on-off switch, which promptly demonstrated that Hg signals could only be detected upon activation of the plasma discharge. In parallel, adsorption of MeHg⁺ to PM-loaded glass fiber filters was investigated. Direct analysis of methylmercury-impregnated PM resulted in significant signal suppression compared to the same mass of analyte from an aqueous standard, which suggests that methylmercury is efficiently adsorbed on PM. This was later confirmed by repeating the same experiment with “blank” (PM-free) glass fiber filters. Hence, extraction of methylmercury to a liquid phase was required for quantification. In order to demonstrate the feasibility of the proposed setup to carry out methylmercury detection in the presence oh Hg²⁺, recovery tests were conducted by mixing MeHg⁺ with Hg²⁺ at three distinct concentration levels (100 : 1, 10 : 1 and 1 : 1 MeHg⁺ : Hg²⁺). Recoveries better than 91% were obtained for MeHg⁺ under these conditions, which demonstrates that the device is efficient for MeHg⁺ determination by simply modulating the plasma (switching on-off). Limits of detection and quantification were established as 6 ng and 19 ng, respectively.