DIN ISO 20280:2010-05

This International Standard specifies methods for the determination of arsenic, antimony and selenium, in an aqua regia extract of soil obtained in accordance with ISO 11466, by electrothermal or hydride-generation atomic absorption spectrometry. Arsenic, antimony and selenium are extracted from soil samples with aqua regia according to ISO 11466. Arsenic, antimony and selenium are determined by electrothermal atomic absorption spectrometry (ETAAS), in which discrete volumes of sample solution are dispensed into a graphite tube. By increasing the temperature of this graphite tube stepwise, the processes of drying, thermal decomposition of the matrix and thermal dissociation into free atoms occur. The resulting absorption signal should (under optimum conditions) be a sharp symmetrical peak proportional to the element concentration in solution. Alternatively, arsenic, antimony and selenium are determined by the hydride-generation technique (HGAAS). Arsenic and antimony are first pre-reduced in the aqua regia extract by a mixture of ascorbic acid and potassium iodide. Selenium is pre-reduced by hydrochloric acid at an elevated temperature. The hydride formation occurs by reaction with a sodium borohydride solution. The hydrides are carried from the solution by an argon stream into a heated quartz cell and decomposed at 900 °C and then the atom concentration for arsenic and antimony is measured by atomic absorption spectrometry. There are several commercial systems available where the reaction of hydride formation occurs continuously (continuous flow or flow injection systems) or stepwise (batch systems). All these techniques can be used, but adaptation of the working steps and reagent concentrations according to the advice of the manufacturer may be necessary. At DIN the Committee responsible for this standard is NA 119-01-02-02 UA "Chemische und physikalische Verfahren" ("Chemical and physical methods").