Comparison of Acid Mixtures in High-Pressure Microwave Digestion Methods for the Determination of the Total Mercury in Sediments by Cold-Vapor Atomic Absorption Spectrometry

Abstract

Four closed-vessel microwave digestion methods were compared for the accurate determination of mercury in sediments by flow-injection cold-vapor atomic absorption spectrometry. The results showed that several acid mixtures (HNO₃/H₂SO₄, HNO₃/HClO₄, HCl/HNO₃ and HCl/HNO₃/HF) completely digested the soil matrix for the determination of mercury. The method using aqua regia is preferred because it is time saving, less dangerous and suitable for other trace-metal analyses. The merits of pressure-feedback microwave digestion is that it simplifies soil sample digestion, and there is no loss of mercury. The digestion methods were evaluated by determining mercury in NIST SRM 1645 River Sediment, NIES CRM No. 2 Pond Sediment and NRCC BCSS-1 Marine Sediment. Recoveries of 92-108% were achieved. Good recoveries of 94-104% were also obtained for soil and marine-sediment samples spiked with different species of mercury.