This International Standard specifies a method for microwave-assisted extraction of elements from samples using aqua regia as the extraction solution for the determination of elements. This method is applicable to all types of soil and soil material. Aqua regia extraction is suitable for the release of trace and major element fractions in soil. Aqua regia is not suitable for the extraction of elements from refractory compounds, such as SiO2, TiO2 and Al2O3. The extraction with aqua regia is operationally defined and will not necessarily release all elements completely. The microwave method is generic and can be implemented using a wide variety of equipment, provided: a) the extraction mixture ratio is unchanged; b) the extraction temperature is known. Solutions produced by the microwave method are suitable for analysis, for example, by using atomic absorption spectrometry (flame: FAAS, hydride generation: HGAAS, cold vapour: CVAAS, graphite furnace; GFAAS), inductively coupled plasma emission spectrometry (ICP/OES) and inductively coupled plasma mass spectrometry (ICP/MS). NOTE Due to the presence of chloride in the extraction solution, limitations for the application of analytical techniques can occur.