There are not many high-sensitivity direct determination methods of trace elements in seawater, and there are a lot of matrix salts in seawater, so it is difficult to get reliable results. Separation and enrichment are usually used to eliminate interference and improve the concentration of trace elements to be measured before determination. The common methods of enrichment and separation are solvent extraction, ion exchange, precipitation and freeze drying. ① Solvent extraction method. For example, ammonium pyrrolidone-methyl isobutyl ketone can be used to extract cadmium, copper, nickel, lead, zinc, silver, cobalt, iron and other elements in seawater for atomic absorption spectrophotometry. ② ion exchange method. Cellulose exchange method can enrich cobalt, chromium, copper, iron, molybdenum, nickel, lead, zinc, uranium and other elements in seawater, and is used in X-ray fluorescence method and neutron activation method. Chelating resin exchange method can enrich cadmium, chromium, copper, iron, manganese, nickel, lead, zinc and other elements for atomic absorption spectrophotometry. ③ * * * precipitation method. Before the determination of trace elements in seawater by spectrophotometry, atomic absorption spectrometry or neutron activation method, precipitation method can be used for enrichment and separation. If ferric hydroxide is used as precipitant, arsenic, europium, lanthanum, ruthenium, tin and tantalum are separated from seawater, and then their contents are determined by neutron activation method. ④ Freeze-drying method. Before the determination of various elements in seawater by neutron activation method, it can be used for enrichment, but it cannot separate interfering elements.