Test methods: Weigh 0.1g soil standard sample GBW-07401(GSS-1), put it into a 50ml polytetrafluoroethylene digestion tube, add about 1ml of high-purity solvent to wet the soil, and shake well. Put the sample tube into the graphite digester for digestion. after the digestion, filter the prepared samples to be tested. the acid system is: aqua regia (6ml hydrochloric acid: 2ml nitric acid) Shake once every 30min in the digestion stage about 1ml of acid remains, cool to volume the constant volume is 25ml