Methods for determination and lowering of blanks in reagents used for determination of mercury

Abstract

The total blank in reagents used for mercury determination is sometimes higher than the content of mercury in a sample. Methods for determination of mercury blanks and reducing the mercury contents in the reagents used frequently for digestion of biological materials and natural waters are presented. To determine the mercury blank in reagents, following method was used. Appropriate amounts of H₂SO₄ and SnCl₂ solutions were added to pure water in a flask, and the mercury in the solution was expelled by bubbling nitrogen gas. A certain amount of a reagent solution of which mercury concentration was to be determined was added, and the mercury vaporized by bubbling nitrogen gas was collected on silver powder. The silver was heated and the released mercury was determined by atomic absorption spectro-photometry. The following methods were used to reduce mercury concentration in the reagents. To a 100 ml solution of H₂SO₄, HCl, NH₂OH·HCl, NaCl or water, 5 g of Unicellex chelating resin was added. To a 100 ml solution of H₂SO₄ or NH₂OH·HCl, 5 g of charcoal (200 mesh) was added. The solutions were shaken for 30 or 60 min, or allowed to stand for one day with occasional shaking. In the case of using the resin, the supernatant was used, and in the case of charcoal the solution was centrifuged. A small amount of sodium oxalate was added to a permanganate solution, followed by boiling for 2 h and filtration through a Millipore filter (0.45 μm). Nitrogen gas was passed through a SnCl₂ solution. Sub-boiling distillation method was adopted for HNO₃. Generally, the mercury concentrations in the reagents were reduced by one order of magnitude.