ÖNORM EN 12338

This European Standard specifies the determination of mercury in two parts which use either tin(ll)chloride or sodium tetrahydroborate as reducing agent. The methods described in clauses 4 and 5 are suitable for the determination of mercury in water, for example in ground, surface and waste waters, in the concentration range from 0,01 pg/l to 1 pg/I. Higher concentrations may be determined if the water sample is diluted. The total mercury content of water is determined after digestion of the sample. If only soluble mercury compounds are to be determined, a filtration step using a 0,45 pm membrane filter is applied prior to digestion. Mono- or divalent mercury is reduced to the elemental form by a reducing agent such as tin(ll) chloride, SnCl or sodium tetrahydroborate, NaBH in an acid medium. Elemental mercury is then stripped from the solution with the aid of a stream of inert gas and transported over a noble metal surface with a large area, such as goldlplatinum gauze, on which the mercury is adsorbed. The mercury is released by rapid heating of the adsorbant and further transported in a stream of carrier gas to a suitable cuvette. Absorbances are measured at a wavelength of 253,7 nm in the radiation beam of an atomic absorption spectrometer. Concentrations are calculated using a calibration curve. In order to fully decompose all of the mercury compounds, a digestion procedure is required. Digestion can be omitted only if it is certain that the mercury concentration may be measured without this pretreatment.