Development of an electrothermal vaporizer for direct mercury determination in soil by inductively-coupled plasma mass spectrometry

Abstract The need to determine mercury in environmental samples is well known, along with its related difficulty. Most methods require samples to be decomposed, involving the use of concentrated acids; this requires considerable time and is liable to lead to analyte loss. The aim of this work is to develop a simple electrothermal vaporization (ETV) system coupled to inductively coupled plasma mass spectrometry (ICP-MS) for Hg determination by direct solid sample analysis (DSSA). The ETV system consists of a high-power lamp enclosed in glass chamber equipped with solenoid valves to control the flow of argon gas (Ar) during pyrolysis and vaporization steps. The system is controlled by a printed circuit board and software developed in the LabVIEW environment. In this system, the analyte vapour was extracted through a glass tube positioned just above the sample, avoiding the analyte deposition on the chamber wall and consequently reducing memory effect. The heating program was optimised and the pyrolysis step was not necessary since it was possible to vaporize the analyte at relatively low temperature (700 °C) without matrix interference. Soil mass between 0.500 and 5.000 mg can be analysed with the ETV system. Calibration was carried out by using a certified reference material (CRM) of soil (NIST2709) ranged from 0.1 to 1.0 ng of Hg. The relative standard deviation was lower than 20% (n = 3) and the limit of quantification (10σ) of Hg was 3.1 ng g −1 . The accuracy was evaluated by comparison of results obtained for Hg in CRMs and no statistical differences were observed (paired t -test at a confidence level of 95%). To evaluate the performance of ETV system, soil samples with different concentration levels were analysed and the results were in good agreement (paired t -test at a confidence level of 95%) with those obtained by nebulization-ICP-MS (NEB-ICP-MS) after acid extraction. Therefore, the proposed method can be used for routine analysis, where the time of analysis of approximately 60 s per sample, risk of contamination, analyte losses and generation of residues are drastically reduced in comparison with techniques that require sample extraction for Hg determination by NEB-ICP-MS.